From 7311ed01b68ba942f2f5929550630d71542ebae8 Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Wed, 22 Feb 2023 20:14:57 -0500
Subject: [PATCH 01/40] Use SetCurrentValue() in ColorPicker controls

---
 .../ColorPreviewer/ColorPreviewer.cs               |  2 +-
 .../ColorSlider/ColorSlider.cs                     | 12 ++++++------
 .../ColorSpectrum/ColorSpectrum.cs                 | 14 +++++++-------
 .../ColorView/ColorView.cs                         | 14 +++++++-------
 4 files changed, 21 insertions(+), 21 deletions(-)

diff --git a/src/Avalonia.Controls.ColorPicker/ColorPreviewer/ColorPreviewer.cs b/src/Avalonia.Controls.ColorPicker/ColorPreviewer/ColorPreviewer.cs
index 6f49430505..58702ecb61 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorPreviewer/ColorPreviewer.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorPreviewer/ColorPreviewer.cs
@@ -124,7 +124,7 @@ namespace Avalonia.Controls.Primitives
             if (accentStep != 0)
             {
                 // ColorChanged will be invoked in OnPropertyChanged if the value is different
-                HsvColor = AccentColorConverter.GetAccent(hsvColor, accentStep);
+                SetCurrentValue(HsvColorProperty, AccentColorConverter.GetAccent(hsvColor, accentStep));
             }
         }
     }
diff --git a/src/Avalonia.Controls.ColorPicker/ColorSlider/ColorSlider.cs b/src/Avalonia.Controls.ColorPicker/ColorSlider/ColorSlider.cs
index dd5e7d5b01..7cbadcdf6d 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorSlider/ColorSlider.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorSlider/ColorSlider.cs
@@ -373,7 +373,7 @@ namespace Avalonia.Controls.Primitives
                 ignorePropertyChanged = true;
 
                 // Always keep the two color properties in sync
-                HsvColor = Color.ToHsv();
+                SetCurrentValue(HsvColorProperty, Color.ToHsv());
 
                 SetColorToSliderValues();
                 UpdateBackground();
@@ -403,7 +403,7 @@ namespace Avalonia.Controls.Primitives
                 ignorePropertyChanged = true;
 
                 // Always keep the two color properties in sync
-                Color = HsvColor.ToRgb();
+                SetCurrentValue(ColorProperty, HsvColor.ToRgb());
 
                 SetColorToSliderValues();
                 UpdateBackground();
@@ -440,13 +440,13 @@ namespace Avalonia.Controls.Primitives
 
                 if (ColorModel == ColorModel.Hsva)
                 {
-                    HsvColor = hsvColor;
-                    Color = hsvColor.ToRgb();
+                    SetCurrentValue(HsvColorProperty, hsvColor);
+                    SetCurrentValue(ColorProperty, hsvColor.ToRgb());
                 }
                 else
                 {
-                    Color = color;
-                    HsvColor = color.ToHsv();
+                    SetCurrentValue(ColorProperty, color);
+                    SetCurrentValue(HsvColorProperty, color.ToHsv());
                 }
 
                 UpdatePseudoClasses();
diff --git a/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.cs b/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.cs
index 6f4c0003a8..fde011bc46 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.cs
@@ -403,7 +403,7 @@ namespace Avalonia.Controls.Primitives
 
                     _updatingHsvColor = true;
                     Hsv newHsv = (new Rgb(color)).ToHsv();
-                    HsvColor = newHsv.ToHsvColor(color.A / 255.0);
+                    SetCurrentValue(HsvColorProperty, newHsv.ToHsvColor(color.A / 255.0));
                     _updatingHsvColor = false;
 
                     UpdateEllipse();
@@ -509,15 +509,15 @@ namespace Avalonia.Controls.Primitives
                 {
                     case ColorSpectrumComponents.HueSaturation:
                     case ColorSpectrumComponents.SaturationHue:
-                        ThirdComponent = (ColorComponent)HsvComponent.Value;
+                        SetCurrentValue(ThirdComponentProperty, (ColorComponent)HsvComponent.Value);
                         break;
                     case ColorSpectrumComponents.HueValue:
                     case ColorSpectrumComponents.ValueHue:
-                        ThirdComponent = (ColorComponent)HsvComponent.Saturation;
+                        SetCurrentValue(ThirdComponentProperty, (ColorComponent)HsvComponent.Saturation);
                         break;
                     case ColorSpectrumComponents.SaturationValue:
                     case ColorSpectrumComponents.ValueSaturation:
-                        ThirdComponent = (ColorComponent)HsvComponent.Hue;
+                        SetCurrentValue(ThirdComponentProperty, (ColorComponent)HsvComponent.Hue);
                         break;
                 }
 
@@ -534,7 +534,7 @@ namespace Avalonia.Controls.Primitives
             _updatingColor = true;
             Rgb newRgb = (new Hsv(hsvColor)).ToRgb();
 
-            Color = newRgb.ToColor(hsvColor.A);
+            SetCurrentValue(ColorProperty, newRgb.ToColor(hsvColor.A));
 
             _updatingColor = false;
 
@@ -608,8 +608,8 @@ namespace Avalonia.Controls.Primitives
             Rgb newRgb = newHsv.ToRgb();
             double alpha = HsvColor.A;
 
-            Color = newRgb.ToColor(alpha);
-            HsvColor = newHsv.ToHsvColor(alpha);
+            SetCurrentValue(ColorProperty, newRgb.ToColor(alpha));
+            SetCurrentValue(HsvColorProperty, newHsv.ToHsvColor(alpha));
 
             UpdateEllipse();
             UpdatePseudoClasses();
diff --git a/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs b/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
index 977b1f5c84..38be6cfc5b 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
@@ -50,7 +50,7 @@ namespace Avalonia.Controls
 
                 if (convertedColor is Color color)
                 {
-                    Color = color;
+                    SetCurrentValue(ColorProperty, color);
                 }
 
                 // Re-apply the hex value
@@ -167,7 +167,7 @@ namespace Avalonia.Controls
                 // The work-around for this is done here where SelectedIndex is forcefully
                 // synchronized with whatever the TabControl property value is. This is
                 // possible since selection validation is already done by this method.
-                SelectedIndex = _tabControl.SelectedIndex;
+                SetCurrentValue(SelectedIndexProperty, _tabControl.SelectedIndex);
             }
 
             return;
@@ -211,7 +211,7 @@ namespace Avalonia.Controls
             {
                 ignorePropertyChanged = true;
 
-                HsvColor = Color.ToHsv();
+                SetCurrentValue(HsvColorProperty, Color.ToHsv());
                 SetColorToHexTextBox();
 
                 OnColorChanged(new ColorChangedEventArgs(
@@ -224,7 +224,7 @@ namespace Avalonia.Controls
             {
                 ignorePropertyChanged = true;
 
-                Color = HsvColor.ToRgb();
+                SetCurrentValue(ColorProperty, HsvColor.ToRgb());
                 SetColorToHexTextBox();
 
                 OnColorChanged(new ColorChangedEventArgs(
@@ -241,7 +241,7 @@ namespace Avalonia.Controls
                 // bound properties controlling the palette grid
                 if (palette != null)
                 {
-                    PaletteColumnCount = palette.ColorCount;
+                    SetCurrentValue(PaletteColumnCountProperty, palette.ColorCount);
 
                     List<Color> newPaletteColors = new List<Color>();
                     for (int shadeIndex = 0; shadeIndex < palette.ShadeCount; shadeIndex++)
@@ -252,14 +252,14 @@ namespace Avalonia.Controls
                         }
                     }
 
-                    PaletteColors = newPaletteColors;
+                    SetCurrentValue(PaletteColorsProperty, newPaletteColors);
                 }
             }
             else if (change.Property == IsAlphaEnabledProperty)
             {
                 // Manually coerce the HsvColor value
                 // (Color will be coerced automatically if HsvColor changes)
-                HsvColor = OnCoerceHsvColor(HsvColor);
+                SetCurrentValue(HsvColorProperty,  OnCoerceHsvColor(HsvColor));
             }
             else if (change.Property == IsColorComponentsVisibleProperty ||
                      change.Property == IsColorPaletteVisibleProperty ||

From 76e0e54a0008ae81cd3a9daf36c7a89568a9c323 Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Tue, 7 Mar 2023 23:46:39 -0500
Subject: [PATCH 02/40] Restore ColorPicker flyout top placement

Default behavior was changed after https://github.com/AvaloniaUI/Avalonia/pull/10492
---
 .../Themes/Fluent/ColorPicker.xaml                             | 3 ++-
 .../Themes/Simple/ColorPicker.xaml                             | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorPicker.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorPicker.xaml
index 8f52b059f1..e6b25fa387 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorPicker.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorPicker.xaml
@@ -42,7 +42,8 @@
             </Panel>
           </DropDownButton.Content>
           <DropDownButton.Flyout>
-            <Flyout FlyoutPresenterClasses="nopadding">
+            <Flyout FlyoutPresenterClasses="nopadding"
+                    Placement="Top">
 
               <!-- The following is copy-pasted from the ColorView's control template.
                    It MUST always be kept in sync with the ColorView (which is master).
diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorPicker.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorPicker.xaml
index d44902dd70..b801f82a44 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorPicker.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorPicker.xaml
@@ -42,7 +42,7 @@
             </Panel>
           </DropDownButton.Content>
           <DropDownButton.Flyout>
-            <Flyout>
+            <Flyout Placement="Top">
 
               <!-- The following is copy-pasted from the ColorView's control template.
                    It MUST always be kept in sync with the ColorView (which is master).

From dc52c0b66cdda90a3036d79bbe6bd1af66a86521 Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Tue, 14 Mar 2023 09:06:08 -0400
Subject: [PATCH 03/40] Match color model control height with the hex TextBox

---
 .../Themes/Fluent/ColorPicker.xaml                              | 2 ++
 src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml  | 2 ++
 .../Themes/Simple/ColorPicker.xaml                              | 2 ++
 src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorView.xaml  | 2 ++
 4 files changed, 8 insertions(+)

diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorPicker.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorPicker.xaml
index e6b25fa387..fd3a87c185 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorPicker.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorPicker.xaml
@@ -217,6 +217,7 @@
                                        Content="RGB"
                                        CornerRadius="4,0,0,4"
                                        BorderThickness="1,1,0,1"
+                                       Height="{Binding ElementName=PART_HexTextBox, Path=Bounds.Height}"
                                        IsChecked="{TemplateBinding ColorModel, Converter={StaticResource EnumToBoolConverter}, ConverterParameter={x:Static controls:ColorModel.Rgba}, Mode=TwoWay}" />
                           <RadioButton x:Name="HsvRadioButton"
                                        Theme="{StaticResource ColorViewColorModelRadioButtonTheme}"
@@ -224,6 +225,7 @@
                                        Content="HSV"
                                        CornerRadius="0,4,4,0"
                                        BorderThickness="0,1,1,1"
+                                       Height="{Binding ElementName=PART_HexTextBox, Path=Bounds.Height}"
                                        IsChecked="{TemplateBinding ColorModel, Converter={StaticResource EnumToBoolConverter}, ConverterParameter={x:Static controls:ColorModel.Hsva}, Mode=TwoWay}" />
                         </Grid>
                         <Grid x:Name="HexInputGrid"
diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
index fab5415bfb..f35e413da3 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
@@ -465,6 +465,7 @@
                                  Content="RGB"
                                  CornerRadius="4,0,0,4"
                                  BorderThickness="1,1,0,1"
+                                 Height="{Binding ElementName=PART_HexTextBox, Path=Bounds.Height}"
                                  IsChecked="{TemplateBinding ColorModel, Converter={StaticResource EnumToBoolConverter}, ConverterParameter={x:Static controls:ColorModel.Rgba}, Mode=TwoWay}" />
                     <RadioButton x:Name="HsvRadioButton"
                                  Theme="{StaticResource ColorViewColorModelRadioButtonTheme}"
@@ -472,6 +473,7 @@
                                  Content="HSV"
                                  CornerRadius="0,4,4,0"
                                  BorderThickness="0,1,1,1"
+                                 Height="{Binding ElementName=PART_HexTextBox, Path=Bounds.Height}"
                                  IsChecked="{TemplateBinding ColorModel, Converter={StaticResource EnumToBoolConverter}, ConverterParameter={x:Static controls:ColorModel.Hsva}, Mode=TwoWay}" />
                   </Grid>
                   <Grid x:Name="HexInputGrid"
diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorPicker.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorPicker.xaml
index b801f82a44..2bed166bb1 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorPicker.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorPicker.xaml
@@ -216,6 +216,7 @@
                                        Content="RGB"
                                        CornerRadius="0,0,0,0"
                                        BorderThickness="1,1,0,1"
+                                       Height="{Binding ElementName=PART_HexTextBox, Path=Bounds.Height}"
                                        IsChecked="{TemplateBinding ColorModel, Converter={StaticResource EnumToBoolConverter}, ConverterParameter={x:Static controls:ColorModel.Rgba}, Mode=TwoWay}" />
                           <RadioButton x:Name="HsvRadioButton"
                                        Theme="{StaticResource ColorViewColorModelRadioButtonTheme}"
@@ -223,6 +224,7 @@
                                        Content="HSV"
                                        CornerRadius="0,0,0,0"
                                        BorderThickness="0,1,1,1"
+                                       Height="{Binding ElementName=PART_HexTextBox, Path=Bounds.Height}"
                                        IsChecked="{TemplateBinding ColorModel, Converter={StaticResource EnumToBoolConverter}, ConverterParameter={x:Static controls:ColorModel.Hsva}, Mode=TwoWay}" />
                         </Grid>
                         <Grid x:Name="HexInputGrid"
diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorView.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorView.xaml
index 0ce6dd5e04..89de202b09 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorView.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorView.xaml
@@ -427,6 +427,7 @@
                                  Content="RGB"
                                  CornerRadius="0,0,0,0"
                                  BorderThickness="1,1,0,1"
+                                 Height="{Binding ElementName=PART_HexTextBox, Path=Bounds.Height}"
                                  IsChecked="{TemplateBinding ColorModel, Converter={StaticResource EnumToBoolConverter}, ConverterParameter={x:Static controls:ColorModel.Rgba}, Mode=TwoWay}" />
                     <RadioButton x:Name="HsvRadioButton"
                                  Theme="{StaticResource ColorViewColorModelRadioButtonTheme}"
@@ -434,6 +435,7 @@
                                  Content="HSV"
                                  CornerRadius="0,0,0,0"
                                  BorderThickness="0,1,1,1"
+                                 Height="{Binding ElementName=PART_HexTextBox, Path=Bounds.Height}"
                                  IsChecked="{TemplateBinding ColorModel, Converter={StaticResource EnumToBoolConverter}, ConverterParameter={x:Static controls:ColorModel.Hsva}, Mode=TwoWay}" />
                   </Grid>
                   <Grid x:Name="HexInputGrid"

From 101346326277e29293f8065afefd68fcf18f9bc1 Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sat, 18 Mar 2023 15:07:06 -0400
Subject: [PATCH 04/40] Switch ColorHelper.ToDisplayName() to a hue-only
 algorithm

This is not working quite as accurately as expected so will likely be replaced by a hybrid technique next.
---
 .../Helpers/ColorHelper.cs                    | 146 ++++++++++++++----
 1 file changed, 113 insertions(+), 33 deletions(-)

diff --git a/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs b/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs
index c1a03b1b77..0c47a8ed3f 100644
--- a/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs
+++ b/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs
@@ -1,6 +1,6 @@
 using System;
-using System.Globalization;
 using System.Collections.Generic;
+using System.Globalization;
 using Avalonia.Media;
 using Avalonia.Utilities;
 
@@ -11,8 +11,11 @@ namespace Avalonia.Controls.Primitives
     /// </summary>
     public static class ColorHelper
     {
-        private static readonly Dictionary<Color, string> cachedDisplayNames = new Dictionary<Color, string>();
-        private static readonly object cacheMutex = new object();
+        private static readonly Dictionary<Color, string> _cachedDisplayNames = new Dictionary<Color, string>();
+        private static readonly Dictionary<KnownColor, double> _cachedKnownColorHues = new Dictionary<KnownColor, double>();
+        private static readonly Dictionary<KnownColor, string> _cachedKnownColorNames = new Dictionary<KnownColor, string>();
+        private static readonly object _displayNameCacheMutex = new object();
+        private static readonly object _knownColorCacheMutex = new object();
 
         /// <summary>
         /// Gets the relative (perceptual) luminance/brightness of the given color.
@@ -74,37 +77,91 @@ namespace Avalonia.Controls.Primitives
                 Convert.ToByte(Math.Round(color.R / rounding) * rounding),
                 Convert.ToByte(Math.Round(color.G / rounding) * rounding),
                 Convert.ToByte(Math.Round(color.B / rounding) * rounding));
+            var hsvColor = color.ToHsv();
+
+            // Handle extremes that are outside the below algorithm
+            if (color.A == 0x00)
+            {
+                return GetDisplayName(KnownColor.Transparent);
+            }
+            else if (hsvColor.S <= 0.0)
+            {
+                return GetDisplayName(KnownColor.White);
+            }
+            else if (hsvColor.V <= 0.0)
+            {
+                return GetDisplayName(KnownColor.Black);
+            }
 
             // Attempt to use a previously cached display name
-            lock (cacheMutex)
+            lock (_displayNameCacheMutex)
             {
-                if (cachedDisplayNames.TryGetValue(roundedColor, out var displayName))
+                if (_cachedDisplayNames.TryGetValue(roundedColor, out var displayName))
                 {
                     return displayName;
                 }
             }
 
-            // Find the closest known color by measuring 3D Euclidean distance (ignore alpha)
+            // Build KnownColor caches if they don't already exist
+            lock (_knownColorCacheMutex)
+            {
+                if (_cachedKnownColorHues.Count == 0 ||
+                    _cachedKnownColorNames.Count == 0)
+                {
+                    _cachedKnownColorHues.Clear();
+                    _cachedKnownColorNames.Clear();
+
+                    var knownColors = (KnownColor[])Enum.GetValues(typeof(KnownColor));
+                    for (int i = 1; i < knownColors.Length; i++) // Skip 'None' so start at 1
+                    {
+                        KnownColor knownColor = knownColors[i];
+
+                        // Transparent is skipped since alpha is ignored making it equivalent to White
+                        if (knownColor == KnownColor.Transparent)
+                        {
+                            continue;
+                        }
+
+                        double hue = KnownColors.ToColor(knownColor).ToHsv().H;
+
+                        // Some known colors have the same numerical value. For example:
+                        //  - Aqua = 0xff00ffff
+                        //  - Cyan = 0xff00ffff
+                        //
+                        // This is not possible to represent in a dictionary which requires
+                        // unique values. Therefore, only the first value is used.
+
+                        if (!_cachedKnownColorHues.ContainsKey(knownColor))
+                        {
+                            _cachedKnownColorHues.Add(knownColor, hue);
+                        }
+
+                        if (!_cachedKnownColorNames.ContainsKey(knownColor))
+                        {
+                            _cachedKnownColorNames.Add(knownColor, GetDisplayName(knownColor));
+                        }
+                    }
+                }
+            }
+
+            // Find the closest known color by finding nearest Hue
+            // Since Hue is the best measure of human perception of the color itself
+            // it is not necessary to check other components (Saturation, Value).
             var closestKnownColor = KnownColor.None;
-            var closestKnownColorDistance = double.PositiveInfinity;
-            var knownColors = (KnownColor[])Enum.GetValues(typeof(KnownColor));
+            var closestKnownColorHueDiff = double.PositiveInfinity;
 
-            for (int i = 1; i < knownColors.Length; i++) // Skip 'None'
+            lock (_knownColorCacheMutex)
             {
-                // Transparent is skipped since alpha is ignored making it equivalent to White
-                if (knownColors[i] != KnownColor.Transparent)
+                foreach (var hueEntry in _cachedKnownColorHues)
                 {
-                    Color knownColor = KnownColors.ToColor(knownColors[i]);
+                    // Closest hue before or after is allowed
+                    // Therefore, use an absolute value
+                    double difference = Math.Abs(hsvColor.H - hueEntry.Value);
 
-                    double distance = Math.Sqrt(
-                        Math.Pow((double)(roundedColor.R - knownColor.R), 2.0) +
-                        Math.Pow((double)(roundedColor.G - knownColor.G), 2.0) +
-                        Math.Pow((double)(roundedColor.B - knownColor.B), 2.0));
-
-                    if (distance < closestKnownColorDistance)
+                    if (difference < closestKnownColorHueDiff)
                     {
-                        closestKnownColor = knownColors[i];
-                        closestKnownColorDistance = distance;
+                        closestKnownColor = hueEntry.Key;
+                        closestKnownColorHueDiff = difference;
                     }
                 }
             }
@@ -113,26 +170,19 @@ namespace Avalonia.Controls.Primitives
             // Cache results for next time as well
             if (closestKnownColor != KnownColor.None)
             {
-                var sb = StringBuilderCache.Acquire();
-                string name = closestKnownColor.ToString();
+                string displayName;
 
-                // Add spaces converting PascalCase to human-readable names
-                for (int i = 0; i < name.Length; i++)
+                lock (_knownColorCacheMutex)
                 {
-                    if (i != 0 &&
-                        char.IsUpper(name[i]))
+                    if (!_cachedKnownColorNames.TryGetValue(closestKnownColor, out displayName))
                     {
-                        sb.Append(' ');
+                        displayName = GetDisplayName(closestKnownColor);
                     }
-
-                    sb.Append(name[i]);
                 }
 
-                string displayName = StringBuilderCache.GetStringAndRelease(sb);
-
-                lock (cacheMutex)
+                lock (_displayNameCacheMutex)
                 {
-                    cachedDisplayNames.Add(roundedColor, displayName);
+                    _cachedDisplayNames.Add(roundedColor, displayName);
                 }
 
                 return displayName;
@@ -142,5 +192,35 @@ namespace Avalonia.Controls.Primitives
                 return string.Empty;
             }
         }
+
+        /// <summary>
+        /// Gets the human-readable display name for the given <see cref="KnownColor"/>.
+        /// </summary>
+        /// <remarks>
+        /// This currently uses the <see cref="KnownColor"/> enum value's C# name directly
+        /// which limits it to the EN language only. In the future this should be localized
+        /// to other cultures.
+        /// </remarks>
+        /// <param name="knownColor">The <see cref="KnownColor"/> to get the display name for.</param>
+        /// <returns>The human-readable display name for the given <see cref="KnownColor"/>.</returns>
+        private static string GetDisplayName(KnownColor knownColor)
+        {
+            var sb = StringBuilderCache.Acquire();
+            string name = knownColor.ToString();
+
+            // Add spaces converting PascalCase to human-readable names
+            for (int i = 0; i < name.Length; i++)
+            {
+                if (i != 0 &&
+                    char.IsUpper(name[i]))
+                {
+                    sb.Append(' ');
+                }
+
+                sb.Append(name[i]);
+            }
+
+            return StringBuilderCache.GetStringAndRelease(sb);
+        }
     }
 }

From 1b30b26c48000b972a3c7b6e82aecf237c01167c Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sat, 18 Mar 2023 15:09:13 -0400
Subject: [PATCH 05/40] Improve HsvColor saturation remarks

---
 src/Avalonia.Base/Media/HsvColor.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Avalonia.Base/Media/HsvColor.cs b/src/Avalonia.Base/Media/HsvColor.cs
index f97457c54d..df68252065 100644
--- a/src/Avalonia.Base/Media/HsvColor.cs
+++ b/src/Avalonia.Base/Media/HsvColor.cs
@@ -131,7 +131,7 @@ namespace Avalonia.Media
         /// </summary>
         /// <remarks>
         /// <list type="bullet">
-        ///   <item>0 is a shade of gray (no color).</item>
+        ///   <item>0 is fully white (or a shade of gray) and shows no color.</item>
         ///   <item>1 is the full color.</item>
         /// </list>
         /// </remarks>

From bb8e3ae9ab5173aa4575c2f5cce342e44579fe4d Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sat, 18 Mar 2023 15:11:01 -0400
Subject: [PATCH 06/40] Switch ColorSpectrum.ThirdComponent to a read-only
 DirectProperty

---
 .../ColorPicker/ColorPicker.cs                         |  4 +---
 .../ColorSpectrum/ColorSpectrum.Properties.cs          | 10 +++++-----
 .../ColorSpectrum/ColorSpectrum.cs                     |  9 +++++----
 .../ColorView/ColorView.cs                             |  3 ---
 .../Helpers/ColorPickerHelpers.cs                      |  2 --
 5 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/src/Avalonia.Controls.ColorPicker/ColorPicker/ColorPicker.cs b/src/Avalonia.Controls.ColorPicker/ColorPicker/ColorPicker.cs
index 01cb745ba7..92d8535272 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorPicker/ColorPicker.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorPicker/ColorPicker.cs
@@ -1,6 +1,4 @@
-using Avalonia.Controls.Primitives;
-
-namespace Avalonia.Controls
+namespace Avalonia.Controls
 {
     /// <summary>
     /// Presents a color for user editing using a spectrum, palette and component sliders within a drop down.
diff --git a/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.Properties.cs b/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.Properties.cs
index 5c7de2459b..2245eb8022 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.Properties.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.Properties.cs
@@ -96,10 +96,10 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Defines the <see cref="ThirdComponent"/> property.
         /// </summary>
-        public static readonly StyledProperty<ColorComponent> ThirdComponentProperty =
-            AvaloniaProperty.Register<ColorSpectrum, ColorComponent>(
+        public static readonly DirectProperty<ColorSpectrum, ColorComponent> ThirdComponentProperty =
+            AvaloniaProperty.RegisterDirect<ColorSpectrum, ColorComponent>(
                 nameof(ThirdComponent),
-                ColorComponent.Component3); // Value
+                o => o.ThirdComponent);
 
         /// <summary>
         /// Gets or sets the currently selected color in the RGB color model.
@@ -239,8 +239,8 @@ namespace Avalonia.Controls.Primitives
         /// </remarks>
         public ColorComponent ThirdComponent
         {
-            get => GetValue(ThirdComponentProperty);
-            protected set => SetValue(ThirdComponentProperty, value);
+            get => _thirdComponent;
+            private set => SetAndRaise(ThirdComponentProperty, ref _thirdComponent, value);
         }
     }
 }
diff --git a/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.cs b/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.cs
index fde011bc46..9198a2f237 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorSpectrum/ColorSpectrum.cs
@@ -13,9 +13,9 @@ using Avalonia.Interactivity;
 using Avalonia.Layout;
 using Avalonia.Media;
 using Avalonia.Media.Imaging;
+using Avalonia.Reactive;
 using Avalonia.Threading;
 using Avalonia.Utilities;
-using Avalonia.Reactive;
 
 namespace Avalonia.Controls.Primitives
 {
@@ -48,6 +48,7 @@ namespace Avalonia.Controls.Primitives
         private bool _isPointerPressed = false;
         private bool _shouldShowLargeSelection = false;
         private List<Hsv> _hsvValues = new List<Hsv>();
+        private ColorComponent _thirdComponent = ColorComponent.Component3; // HsvComponent.Value
 
         private IDisposable? _layoutRootDisposable;
         private IDisposable? _selectionEllipsePanelDisposable;
@@ -509,15 +510,15 @@ namespace Avalonia.Controls.Primitives
                 {
                     case ColorSpectrumComponents.HueSaturation:
                     case ColorSpectrumComponents.SaturationHue:
-                        SetCurrentValue(ThirdComponentProperty, (ColorComponent)HsvComponent.Value);
+                        ThirdComponent = (ColorComponent)HsvComponent.Value;
                         break;
                     case ColorSpectrumComponents.HueValue:
                     case ColorSpectrumComponents.ValueHue:
-                        SetCurrentValue(ThirdComponentProperty, (ColorComponent)HsvComponent.Saturation);
+                        ThirdComponent = (ColorComponent)HsvComponent.Saturation;
                         break;
                     case ColorSpectrumComponents.SaturationValue:
                     case ColorSpectrumComponents.ValueSaturation:
-                        SetCurrentValue(ThirdComponentProperty, (ColorComponent)HsvComponent.Hue);
+                        ThirdComponent = (ColorComponent)HsvComponent.Hue;
                         break;
                 }
 
diff --git a/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs b/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
index 38be6cfc5b..1d6d5aa008 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
@@ -1,14 +1,11 @@
 using System;
 using System.Collections.Generic;
-using System.Collections.ObjectModel;
 using System.Globalization;
 using Avalonia.Controls.Converters;
 using Avalonia.Controls.Metadata;
-using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Media;
 using Avalonia.Threading;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Controls
 {
diff --git a/src/Avalonia.Controls.ColorPicker/Helpers/ColorPickerHelpers.cs b/src/Avalonia.Controls.ColorPicker/Helpers/ColorPickerHelpers.cs
index 819d745772..dbd92d4ac5 100644
--- a/src/Avalonia.Controls.ColorPicker/Helpers/ColorPickerHelpers.cs
+++ b/src/Avalonia.Controls.ColorPicker/Helpers/ColorPickerHelpers.cs
@@ -4,8 +4,6 @@
 // Licensed to The Avalonia Project under the MIT License.
 
 using System;
-using System.Collections.Generic;
-using System.Linq;
 using System.Runtime.InteropServices;
 using System.Threading.Tasks;
 using Avalonia.Layout;

From a92d7abcc7fd2a6162ef3b36f320896596549e14 Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sat, 18 Mar 2023 16:09:14 -0400
Subject: [PATCH 07/40] Switch ColorHelper.ToDisplayName() to an HSV color
 space algorithm that uses all components

---
 .../Helpers/ColorHelper.cs                    | 120 +++++++++---------
 1 file changed, 60 insertions(+), 60 deletions(-)

diff --git a/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs b/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs
index 0c47a8ed3f..7fa2dfdddd 100644
--- a/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs
+++ b/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs
@@ -11,11 +11,11 @@ namespace Avalonia.Controls.Primitives
     /// </summary>
     public static class ColorHelper
     {
-        private static readonly Dictionary<Color, string> _cachedDisplayNames = new Dictionary<Color, string>();
-        private static readonly Dictionary<KnownColor, double> _cachedKnownColorHues = new Dictionary<KnownColor, double>();
+        private static readonly Dictionary<HsvColor, string> _cachedDisplayNames = new Dictionary<HsvColor, string>();
         private static readonly Dictionary<KnownColor, string> _cachedKnownColorNames = new Dictionary<KnownColor, string>();
         private static readonly object _displayNameCacheMutex = new object();
         private static readonly object _knownColorCacheMutex = new object();
+        private static readonly KnownColor[] _knownColors = (KnownColor[])Enum.GetValues(typeof(KnownColor));
 
         /// <summary>
         /// Gets the relative (perceptual) luminance/brightness of the given color.
@@ -62,7 +62,36 @@ namespace Avalonia.Controls.Primitives
         /// <returns>The approximate color display name.</returns>
         public static string ToDisplayName(Color color)
         {
-            // Without rounding, there are 16,777,216 possible RGB colors (without alpha).
+            var hsvColor = color.ToHsv();
+
+            // Handle extremes that are outside the below algorithm
+            if (color.A == 0x00)
+            {
+                return GetDisplayName(KnownColor.Transparent);
+            }
+
+            // HSV ----------------------------------------------------------------------
+            //
+            // There are far too many possible HSV colors to cache and search through
+            // for performance reasons. Therefore, the HSV color is rounded.
+            // Rounding is tolerable in this algorithm because it is perception based.
+            // Hue is the most important for user perception so is rounded the least.
+            // Then there is a lot of loss in rounding the saturation and value components
+            // which are not as closely related to perceived color.
+            //
+            //         Hue : Round to nearest int (0..360)
+            //  Saturation : Round to the nearest 1/10 (0..1)
+            //       Value : Round to the nearest 1/10 (0..1)
+            //       Alpha : Is ignored in this algorithm
+            //
+            // Rounding results in ~36_000 values to cache in the worse case.
+            //
+            // RGB ----------------------------------------------------------------------
+            //
+            // The original algorithm worked in RGB color space.
+            // If this code is every adjusted to work in RGB again note the following:
+            //
+            // Without rounding, there are 16_777_216 possible RGB colors (without alpha).
             // This is too many to cache and search through for performance reasons.
             // It is also needlessly large as there are only ~140 known/named colors.
             // Therefore, rounding of the input color's component values is done to
@@ -71,58 +100,29 @@ namespace Avalonia.Controls.Primitives
             // The rounding value of 5 is specially chosen.
             // It is a factor of 255 and therefore evenly divisible which improves
             // the quality of the calculations.
-            double rounding = 5;
-            var roundedColor = new Color(
-                0xFF,
-                Convert.ToByte(Math.Round(color.R / rounding) * rounding),
-                Convert.ToByte(Math.Round(color.G / rounding) * rounding),
-                Convert.ToByte(Math.Round(color.B / rounding) * rounding));
-            var hsvColor = color.ToHsv();
-
-            // Handle extremes that are outside the below algorithm
-            if (color.A == 0x00)
-            {
-                return GetDisplayName(KnownColor.Transparent);
-            }
-            else if (hsvColor.S <= 0.0)
-            {
-                return GetDisplayName(KnownColor.White);
-            }
-            else if (hsvColor.V <= 0.0)
-            {
-                return GetDisplayName(KnownColor.Black);
-            }
+            var roundedHsvColor = new HsvColor(
+                1.0,
+                Math.Round(hsvColor.H, 0),
+                Math.Round(hsvColor.S, 1),
+                Math.Round(hsvColor.V, 1));
 
             // Attempt to use a previously cached display name
             lock (_displayNameCacheMutex)
             {
-                if (_cachedDisplayNames.TryGetValue(roundedColor, out var displayName))
+                if (_cachedDisplayNames.TryGetValue(roundedHsvColor, out var displayName))
                 {
                     return displayName;
                 }
             }
 
-            // Build KnownColor caches if they don't already exist
+            // Build the KnownColor name cache if it doesn't already exist
             lock (_knownColorCacheMutex)
             {
-                if (_cachedKnownColorHues.Count == 0 ||
-                    _cachedKnownColorNames.Count == 0)
+                if (_cachedKnownColorNames.Count == 0)
                 {
-                    _cachedKnownColorHues.Clear();
-                    _cachedKnownColorNames.Clear();
-
-                    var knownColors = (KnownColor[])Enum.GetValues(typeof(KnownColor));
-                    for (int i = 1; i < knownColors.Length; i++) // Skip 'None' so start at 1
+                    for (int i = 1; i < _knownColors.Length; i++) // Skip 'None' so start at 1
                     {
-                        KnownColor knownColor = knownColors[i];
-
-                        // Transparent is skipped since alpha is ignored making it equivalent to White
-                        if (knownColor == KnownColor.Transparent)
-                        {
-                            continue;
-                        }
-
-                        double hue = KnownColors.ToColor(knownColor).ToHsv().H;
+                        KnownColor knownColor = _knownColors[i];
 
                         // Some known colors have the same numerical value. For example:
                         //  - Aqua = 0xff00ffff
@@ -131,11 +131,6 @@ namespace Avalonia.Controls.Primitives
                         // This is not possible to represent in a dictionary which requires
                         // unique values. Therefore, only the first value is used.
 
-                        if (!_cachedKnownColorHues.ContainsKey(knownColor))
-                        {
-                            _cachedKnownColorHues.Add(knownColor, hue);
-                        }
-
                         if (!_cachedKnownColorNames.ContainsKey(knownColor))
                         {
                             _cachedKnownColorNames.Add(knownColor, GetDisplayName(knownColor));
@@ -144,24 +139,29 @@ namespace Avalonia.Controls.Primitives
                 }
             }
 
-            // Find the closest known color by finding nearest Hue
-            // Since Hue is the best measure of human perception of the color itself
-            // it is not necessary to check other components (Saturation, Value).
+            // Find the closest known color by measuring 3D Euclidean distance (ignore alpha)
+            // This is done in HSV color space to most closely match user-perception
             var closestKnownColor = KnownColor.None;
-            var closestKnownColorHueDiff = double.PositiveInfinity;
+            var closestKnownColorDistance = double.PositiveInfinity;
 
-            lock (_knownColorCacheMutex)
+            for (int i = 1; i < _knownColors.Length; i++) // Skip 'None' so start at 1
             {
-                foreach (var hueEntry in _cachedKnownColorHues)
+                KnownColor knownColor = _knownColors[i];
+
+                // Transparent is skipped since alpha is ignored making it equivalent to White
+                if (knownColor != KnownColor.Transparent)
                 {
-                    // Closest hue before or after is allowed
-                    // Therefore, use an absolute value
-                    double difference = Math.Abs(hsvColor.H - hueEntry.Value);
+                    HsvColor knownHsvColor = KnownColors.ToColor(knownColor).ToHsv();
+
+                    double distance = Math.Sqrt(
+                        Math.Pow((roundedHsvColor.H - knownHsvColor.H), 2.0) +
+                        Math.Pow((roundedHsvColor.S - knownHsvColor.S), 2.0) +
+                        Math.Pow((roundedHsvColor.V - knownHsvColor.V), 2.0));
 
-                    if (difference < closestKnownColorHueDiff)
+                    if (distance < closestKnownColorDistance)
                     {
-                        closestKnownColor = hueEntry.Key;
-                        closestKnownColorHueDiff = difference;
+                        closestKnownColor = knownColor;
+                        closestKnownColorDistance = distance;
                     }
                 }
             }
@@ -182,7 +182,7 @@ namespace Avalonia.Controls.Primitives
 
                 lock (_displayNameCacheMutex)
                 {
-                    _cachedDisplayNames.Add(roundedColor, displayName);
+                    _cachedDisplayNames.Add(roundedHsvColor, displayName);
                 }
 
                 return displayName;

From 23332cd048507ae602d14c935771e8ddd67252ea Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sun, 19 Mar 2023 00:59:57 -0400
Subject: [PATCH 08/40] Support configurable AlphaComponentPosition in
 ColorView

The default now matches CSS and differs from XAML/WinUI. The CSS trailing alpha component is in wider use for end-users now and it also matches the default slider ordering in the UI.
---
 src/Avalonia.Base/Media/Color.cs              |   2 +-
 .../ColorView/AlphaComponentPosition.cs       |  26 +++
 .../ColorView/ColorView.Properties.cs         |  18 ++
 .../ColorView/ColorView.cs                    |  18 +-
 .../Converters/ColorToHexConverter.cs         | 169 ++++++++++++++++--
 .../Themes/Fluent/ColorView.xaml              |   1 -
 .../Themes/Simple/ColorView.xaml              |   1 -
 7 files changed, 205 insertions(+), 30 deletions(-)
 create mode 100644 src/Avalonia.Controls.ColorPicker/ColorView/AlphaComponentPosition.cs

diff --git a/src/Avalonia.Base/Media/Color.cs b/src/Avalonia.Base/Media/Color.cs
index 74e70b2a14..f06f272e51 100644
--- a/src/Avalonia.Base/Media/Color.cs
+++ b/src/Avalonia.Base/Media/Color.cs
@@ -309,7 +309,7 @@ namespace Avalonia.Media
             if (input.Length == 3 || input.Length == 4)
             {
                 var extendedLength = 2 * input.Length;
-                
+
 #if !BUILDTASK
                 Span<char> extended = stackalloc char[extendedLength];
 #else
diff --git a/src/Avalonia.Controls.ColorPicker/ColorView/AlphaComponentPosition.cs b/src/Avalonia.Controls.ColorPicker/ColorView/AlphaComponentPosition.cs
new file mode 100644
index 0000000000..4f3ae46a24
--- /dev/null
+++ b/src/Avalonia.Controls.ColorPicker/ColorView/AlphaComponentPosition.cs
@@ -0,0 +1,26 @@
+namespace Avalonia.Controls
+{
+    /// <summary>
+    /// Defines the position of a color's alpha component relative to all other components.
+    /// </summary>
+    public enum AlphaComponentPosition
+    {
+        /// <summary>
+        /// The alpha component occurs before all other components.
+        /// </summary>
+        /// <remarks>
+        /// For example, this may indicate the #AARRGGBB or ARGB format which
+        /// is the default format for XAML itself and the Color struct.
+        /// </remarks>
+        Leading,
+
+        /// <summary>
+        /// The alpha component occurs after all other components.
+        /// </summary>
+        /// <remarks>
+        /// For example, this may indicate the #RRGGBBAA or RGBA format which
+        /// is the default format for CSS.
+        /// </remarks>
+        Trailing,
+    }
+}
diff --git a/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.Properties.cs b/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.Properties.cs
index b76059037b..e334a1d323 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.Properties.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.Properties.cs
@@ -42,6 +42,14 @@ namespace Avalonia.Controls
                 nameof(ColorSpectrumShape),
                 ColorSpectrumShape.Box);
 
+        /// <summary>
+        /// Defines the <see cref="HexInputAlphaPosition"/> property.
+        /// </summary>
+        public static readonly StyledProperty<AlphaComponentPosition> HexInputAlphaPositionProperty =
+            AvaloniaProperty.Register<ColorView, AlphaComponentPosition>(
+                nameof(HexInputAlphaPosition),
+                AlphaComponentPosition.Trailing); // Match CSS (and default slider order) instead of XAML/WinUI
+
         /// <summary>
         /// Defines the <see cref="HsvColor"/> property.
         /// </summary>
@@ -260,6 +268,16 @@ namespace Avalonia.Controls
             set => SetValue(ColorSpectrumShapeProperty, value);
         }
 
+        /// <summary>
+        /// Gets or sets the position of the alpha component in the hexadecimal input box relative to
+        /// all other color components.
+        /// </summary>
+        public AlphaComponentPosition HexInputAlphaPosition
+        {
+            get => GetValue(HexInputAlphaPositionProperty);
+            set => SetValue(HexInputAlphaPositionProperty, value);
+        }
+
         /// <inheritdoc cref="ColorSpectrum.HsvColor"/>
         public HsvColor HsvColor
         {
diff --git a/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs b/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
index 1d6d5aa008..274e7f5851 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.Globalization;
 using Avalonia.Controls.Converters;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Primitives;
@@ -25,8 +24,7 @@ namespace Avalonia.Controls
         private TextBox?    _hexTextBox;
         private TabControl? _tabControl;
 
-        private ColorToHexConverter colorToHexConverter = new ColorToHexConverter();
-        protected bool ignorePropertyChanged = false;
+        protected bool _ignorePropertyChanged = false;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ColorView"/> class.
@@ -43,7 +41,7 @@ namespace Avalonia.Controls
         {
             if (_hexTextBox != null)
             {
-                var convertedColor = colorToHexConverter.ConvertBack(_hexTextBox.Text, typeof(Color), null, CultureInfo.CurrentCulture);
+                var convertedColor = ColorToHexConverter.ParseHexString(_hexTextBox.Text ?? string.Empty, HexInputAlphaPosition);
 
                 if (convertedColor is Color color)
                 {
@@ -63,7 +61,7 @@ namespace Avalonia.Controls
         {
             if (_hexTextBox != null)
             {
-                _hexTextBox.Text = colorToHexConverter.Convert(Color, typeof(string), null, CultureInfo.CurrentCulture) as string;
+                _hexTextBox.Text = ColorToHexConverter.ToHexString(Color, HexInputAlphaPosition);
             }
         }
 
@@ -197,7 +195,7 @@ namespace Avalonia.Controls
         /// <inheritdoc/>
         protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
-            if (ignorePropertyChanged)
+            if (_ignorePropertyChanged)
             {
                 base.OnPropertyChanged(change);
                 return;
@@ -206,7 +204,7 @@ namespace Avalonia.Controls
             // Always keep the two color properties in sync
             if (change.Property == ColorProperty)
             {
-                ignorePropertyChanged = true;
+                _ignorePropertyChanged = true;
 
                 SetCurrentValue(HsvColorProperty, Color.ToHsv());
                 SetColorToHexTextBox();
@@ -215,11 +213,11 @@ namespace Avalonia.Controls
                     change.GetOldValue<Color>(),
                     change.GetNewValue<Color>()));
 
-                ignorePropertyChanged = false;
+                _ignorePropertyChanged = false;
             }
             else if (change.Property == HsvColorProperty)
             {
-                ignorePropertyChanged = true;
+                _ignorePropertyChanged = true;
 
                 SetCurrentValue(ColorProperty, HsvColor.ToRgb());
                 SetColorToHexTextBox();
@@ -228,7 +226,7 @@ namespace Avalonia.Controls
                     change.GetOldValue<HsvColor>().ToRgb(),
                     change.GetNewValue<HsvColor>().ToRgb()));
 
-                ignorePropertyChanged = false;
+                _ignorePropertyChanged = false;
             }
             else if (change.Property == PaletteProperty)
             {
diff --git a/src/Avalonia.Controls.ColorPicker/Converters/ColorToHexConverter.cs b/src/Avalonia.Controls.ColorPicker/Converters/ColorToHexConverter.cs
index 8d5f2332be..8798f874f4 100644
--- a/src/Avalonia.Controls.ColorPicker/Converters/ColorToHexConverter.cs
+++ b/src/Avalonia.Controls.ColorPicker/Converters/ColorToHexConverter.cs
@@ -2,6 +2,7 @@
 using System.Globalization;
 using Avalonia.Data.Converters;
 using Avalonia.Media;
+using Avalonia.Utilities;
 
 namespace Avalonia.Controls.Converters
 {
@@ -10,6 +11,11 @@ namespace Avalonia.Controls.Converters
     /// </summary>
     public class ColorToHexConverter : IValueConverter
     {
+        /// <summary>
+        /// Gets or sets the position of a color's alpha component relative to all other components.
+        /// </summary>
+        public AlphaComponentPosition AlphaPosition { get; set; } = AlphaComponentPosition.Leading;
+
         /// <inheritdoc/>
         public object? Convert(
             object? value,
@@ -42,16 +48,7 @@ namespace Avalonia.Controls.Converters
                 return AvaloniaProperty.UnsetValue;
             }
 
-            string hexColor = color.ToUint32().ToString("x8", CultureInfo.InvariantCulture).ToUpperInvariant();
-
-            if (includeSymbol == false)
-            {
-                // TODO: When .net standard 2.0 is dropped, replace the below line
-                //hexColor = hexColor.Replace("#", string.Empty, StringComparison.Ordinal);
-                hexColor = hexColor.Replace("#", string.Empty);
-            }
-
-            return hexColor;
+            return ToHexString(color, AlphaPosition, includeSymbol);
         }
 
         /// <inheritdoc/>
@@ -62,21 +59,159 @@ namespace Avalonia.Controls.Converters
             CultureInfo culture)
         {
             string hexValue = value?.ToString() ?? string.Empty;
+            return ParseHexString(hexValue, AlphaPosition) ?? AvaloniaProperty.UnsetValue;
+        }
+
+        /// <summary>
+        /// Converts the given color to its hex color value string representation.
+        /// </summary>
+        /// <param name="color">The color to represent as a hex value string.</param>
+        /// <param name="alphaPosition">The output position of the alpha component.</param>
+        /// <param name="includeSymbol">Whether the hex symbol '#' will be added.</param>
+        /// <returns>The input color converted to its hex value string.</returns>
+        public static string ToHexString(
+            Color color,
+            AlphaComponentPosition alphaPosition,
+            bool includeSymbol = false)
+        {
+            uint intColor;
+            if (alphaPosition == AlphaComponentPosition.Trailing)
+            {
+                intColor = ((uint)color.R << 24) | ((uint)color.G << 16) | ((uint)color.B << 8) | (uint)color.A;
+            }
+            else
+            {
+                // Default is Leading alpha
+                intColor = ((uint)color.A << 24) | ((uint)color.R << 16) | ((uint)color.G << 8) | (uint)color.B;
+            }
 
-            if (Color.TryParse(hexValue, out Color color))
+            string hexColor = intColor.ToString("x8", CultureInfo.InvariantCulture).ToUpperInvariant();
+
+            if (includeSymbol)
+            {
+                hexColor = '#' + hexColor;
+            }
+
+            return hexColor;
+        }
+
+        /// <summary>
+        /// Parses a hex color value string into a new <see cref="Color"/>.
+        /// </summary>
+        /// <param name="hexColor">The hex color string to parse.</param>
+        /// <param name="alphaPosition">The input position of the alpha component.</param>
+        /// <returns>The parsed <see cref="Color"/>; otherwise, null.</returns>
+        public static Color? ParseHexString(
+            string hexColor,
+            AlphaComponentPosition alphaPosition)
+        {
+            hexColor = hexColor.Trim();
+
+            if (!hexColor.StartsWith("#", StringComparison.Ordinal))
+            {
+                hexColor = "#" + hexColor;
+            }
+
+            if (TryParseHexFormat(hexColor.AsSpan(), alphaPosition, out Color color))
             {
                 return color;
             }
-            else if (hexValue.StartsWith("#", StringComparison.Ordinal) == false &&
-                     Color.TryParse("#" + hexValue, out Color color2))
+
+            return null;
+        }
+
+        /// <summary>
+        /// Parses the given span of characters representing a hex color value into a new <see cref="Color"/>.
+        /// </summary>
+        /// <remarks>
+        /// This is based on the Color.TryParseHexFormat() method.
+        /// It is copied because it needs to be extended to handle alpha position.
+        /// However, the alpha position enum is only available in the controls namespace with the ColorPicker control.
+        /// </remarks>
+        private static bool TryParseHexFormat(
+            ReadOnlySpan<char> s,
+            AlphaComponentPosition alphaPosition,
+            out Color color)
+        {
+            static bool TryParseCore(ReadOnlySpan<char> input, AlphaComponentPosition alphaPosition, ref Color color)
             {
-                return color2;
+                var alphaComponent = 0u;
+
+                if (input.Length == 6)
+                {
+                    if (alphaPosition == AlphaComponentPosition.Trailing)
+                    {
+                        alphaComponent = 0x000000FF;
+                    }
+                    else
+                    {
+                        alphaComponent = 0xFF000000;
+                    }
+                }
+                else if (input.Length != 8)
+                {
+                    return false;
+                }
+
+                if (!input.TryParseUInt(NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var parsed))
+                {
+                    return false;
+                }
+
+                if (alphaComponent != 0)
+                {
+                    if (alphaPosition == AlphaComponentPosition.Trailing)
+                    {
+                        parsed = (parsed << 8) | alphaComponent;
+                    }
+                    else
+                    {
+                        parsed = parsed | alphaComponent;
+                    }
+                }
+
+                if (alphaPosition == AlphaComponentPosition.Trailing)
+                {
+                    // #RRGGBBAA
+                    color = new Color(
+                        a: (byte)(parsed & 0xFF),
+                        r: (byte)((parsed >> 24) & 0xFF),
+                        g: (byte)((parsed >> 16) & 0xFF),
+                        b: (byte)((parsed >> 8) & 0xFF));
+                }
+                else
+                {
+                    // #AARRGGBB
+                    color = new Color(
+                        a: (byte)((parsed >> 24) & 0xFF),
+                        r: (byte)((parsed >> 16) & 0xFF),
+                        g: (byte)((parsed >> 8) & 0xFF),
+                        b: (byte)(parsed & 0xFF));
+                }
+
+                return true;
             }
-            else
+
+            color = default;
+
+            ReadOnlySpan<char> input = s.Slice(1);
+
+            // Handle shorthand cases like #FFF (RGB) or #FFFF (ARGB).
+            if (input.Length == 3 || input.Length == 4)
             {
-                // Invalid hex color value provided
-                return AvaloniaProperty.UnsetValue;
+                var extendedLength = 2 * input.Length;
+                Span<char> extended = stackalloc char[extendedLength];
+
+                for (int i = 0; i < input.Length; i++)
+                {
+                    extended[2 * i + 0] = input[i];
+                    extended[2 * i + 1] = input[i];
+                }
+
+                return TryParseCore(extended, alphaPosition, ref color);
             }
+
+            return TryParseCore(input, alphaPosition, ref color);
         }
     }
 }
diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
index a7d84441aa..f72fb11bbe 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
@@ -8,7 +8,6 @@
 
   <pc:ContrastBrushConverter x:Key="ContrastBrushConverter" />
   <converters:ColorToDisplayNameConverter x:Key="ColorToDisplayNameConverter" />
-  <converters:ColorToHexConverter x:Key="ColorToHexConverter" />
   <converters:DoNothingForNullConverter x:Key="DoNothingForNullConverter" />
   <globalization:NumberFormatInfo x:Key="ColorViewComponentNumberFormat" NumberDecimalDigits="0" />
   <x:Double x:Key="ColorViewTabStripHeight">48</x:Double>
diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorView.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorView.xaml
index ab7288dd8f..4e219a98af 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorView.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorView.xaml
@@ -8,7 +8,6 @@
 
   <pc:ContrastBrushConverter x:Key="ContrastBrushConverter" />
   <converters:ColorToDisplayNameConverter x:Key="ColorToDisplayNameConverter" />
-  <converters:ColorToHexConverter x:Key="ColorToHexConverter" />
   <converters:DoNothingForNullConverter x:Key="DoNothingForNullConverter" />
   <globalization:NumberFormatInfo x:Key="ColorViewComponentNumberFormat" NumberDecimalDigits="0" />
   <x:Double x:Key="ColorViewTabStripHeight">48</x:Double>

From 0b69ab1a3c1d5d98b3ceb425c4c0684e5e5899be Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sun, 19 Mar 2023 11:57:23 -0400
Subject: [PATCH 09/40] Allow derived controls access to Slider template parts
 and state

---
 src/Avalonia.Controls/Slider.cs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/Avalonia.Controls/Slider.cs b/src/Avalonia.Controls/Slider.cs
index 7de726a932..b7f7566e21 100644
--- a/src/Avalonia.Controls/Slider.cs
+++ b/src/Avalonia.Controls/Slider.cs
@@ -86,10 +86,10 @@ namespace Avalonia.Controls
             TickBar.TicksProperty.AddOwner<Slider>();
 
         // Slider required parts
-        private bool _isDragging;
-        private Track? _track;
-        private Button? _decreaseButton;
-        private Button? _increaseButton;
+        protected bool _isDragging;
+        protected Track? _track;
+        protected Button? _decreaseButton;
+        protected Button? _increaseButton;
         private IDisposable? _decreaseButtonPressDispose;
         private IDisposable? _decreaseButtonReleaseDispose;
         private IDisposable? _increaseButtonSubscription;

From 927e5ff77da1437669405e9cf2d506addbc76cea Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sun, 19 Mar 2023 11:58:10 -0400
Subject: [PATCH 10/40] Calculate the ColorSlider spectrum based on the track
 size

---
 .../ColorSlider/ColorSlider.cs                 | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/Avalonia.Controls.ColorPicker/ColorSlider/ColorSlider.cs b/src/Avalonia.Controls.ColorPicker/ColorSlider/ColorSlider.cs
index 7cbadcdf6d..ce47a797ec 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorSlider/ColorSlider.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorSlider/ColorSlider.cs
@@ -96,8 +96,22 @@ namespace Avalonia.Controls.Primitives
             // independent pixels of controls.
 
             var scale = LayoutHelper.GetLayoutScale(this);
-            var pixelWidth = Convert.ToInt32(Bounds.Width * scale);
-            var pixelHeight = Convert.ToInt32(Bounds.Height * scale);
+            int pixelWidth;
+            int pixelHeight;
+
+            if (base._track != null)
+            {
+                pixelWidth = Convert.ToInt32(base._track.Bounds.Width * scale);
+                pixelHeight = Convert.ToInt32(base._track.Bounds.Height * scale);
+            }
+            else
+            {
+                // As a fallback, attempt to calculate using the overall control size
+                // This shouldn't happen as a track is a required template part of a slider
+                // However, if it does, the spectrum will still be shown
+                pixelWidth = Convert.ToInt32(Bounds.Width * scale);
+                pixelHeight = Convert.ToInt32(Bounds.Height * scale);
+            }
 
             if (pixelWidth != 0 && pixelHeight != 0)
             {

From 0bdd79b964c62a9192b68aed9b1bbab6b9bf96fd Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sun, 19 Mar 2023 12:40:33 -0400
Subject: [PATCH 11/40] Update ColorSlider ControlTheme

1. Support lightweight resources to change track and control size independently
2. Make the background spectrum follow the track size
---
 .../Themes/Fluent/ColorSlider.xaml            | 67 +++++++++++--------
 .../Themes/Simple/ColorSlider.xaml            | 67 +++++++++++--------
 2 files changed, 76 insertions(+), 58 deletions(-)

diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorSlider.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorSlider.xaml
index 7e25bd8051..789473571b 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorSlider.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorSlider.xaml
@@ -1,13 +1,20 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
 
+  <!-- Note that the Slider thumb should generally follow the overall Slider dimensions.
+       Therefore, there are not currently separate resources to control it. -->
+  <x:Double x:Key="ColorSliderSize">20</x:Double>
+  <x:Double x:Key="ColorSliderTrackSize">20</x:Double>
+  <CornerRadius x:Key="ColorSliderCornerRadius">10</CornerRadius>
+  <CornerRadius x:Key="ColorSliderTrackCornerRadius">10</CornerRadius>
+
   <ControlTheme x:Key="ColorSliderThumbTheme"
                 TargetType="Thumb">
     <Setter Property="Background" Value="Transparent" />
     <Setter Property="BorderBrush" Value="{DynamicResource SystemControlForegroundBaseHighBrush}" />
     <!--TODO: <Setter Property="BorderBrush" Value="{DynamicResource ColorControlDefaultSelectorBrush}" />-->
     <Setter Property="BorderThickness" Value="3" />
-    <Setter Property="CornerRadius" Value="10" />
+    <Setter Property="CornerRadius" Value="{DynamicResource ColorSliderCornerRadius}" />
     <Setter Property="Template">
       <Setter.Value>
         <ControlTemplate>
@@ -25,27 +32,28 @@
 
     <Style Selector="^:horizontal">
       <Setter Property="BorderThickness" Value="0" />
-      <Setter Property="CornerRadius" Value="10" />
-      <Setter Property="Height" Value="20" />
+      <Setter Property="CornerRadius" Value="{DynamicResource ColorSliderCornerRadius}" />
+      <Setter Property="Height" Value="{DynamicResource ColorSliderSize}" />
       <Setter Property="Template">
         <ControlTemplate TargetType="{x:Type ColorSlider}">
           <Border BorderThickness="{TemplateBinding BorderThickness}"
                   BorderBrush="{TemplateBinding BorderBrush}"
                   CornerRadius="{TemplateBinding CornerRadius}">
             <Grid Margin="{TemplateBinding Padding}">
-              <Rectangle HorizontalAlignment="Stretch"
-                         VerticalAlignment="Stretch"
-                         Fill="{StaticResource ColorControlCheckeredBackgroundBrush}"
-                         RadiusX="{TemplateBinding CornerRadius, Converter={StaticResource TopLeftCornerRadiusConverter}}"
-                         RadiusY="{TemplateBinding CornerRadius, Converter={StaticResource BottomRightCornerRadiusConverter}}" />
-              <Rectangle HorizontalAlignment="Stretch"
-                         VerticalAlignment="Stretch"
-                         Fill="{TemplateBinding Background}"
-                         RadiusX="{TemplateBinding CornerRadius, Converter={StaticResource TopLeftCornerRadiusConverter}}"
-                         RadiusY="{TemplateBinding CornerRadius, Converter={StaticResource BottomRightCornerRadiusConverter}}" />
+              <Border HorizontalAlignment="Stretch"
+                      VerticalAlignment="Center"
+                      Height="{Binding ElementName=PART_Track, Path=Bounds.Height}"
+                      Background="{StaticResource ColorControlCheckeredBackgroundBrush}"
+                      CornerRadius="{DynamicResource ColorSliderTrackCornerRadius}" />
+              <Border HorizontalAlignment="Stretch"
+                      VerticalAlignment="Center"
+                      Height="{Binding ElementName=PART_Track, Path=Bounds.Height}"
+                      Background="{TemplateBinding Background}"
+                      CornerRadius="{DynamicResource ColorSliderTrackCornerRadius}" />
               <Track Name="PART_Track"
+                     Height="{DynamicResource ColorSliderTrackSize}"
                      HorizontalAlignment="Stretch"
-                     VerticalAlignment="Stretch"
+                     VerticalAlignment="Center"
                      Minimum="{TemplateBinding Minimum}"
                      Maximum="{TemplateBinding Maximum}"
                      Value="{TemplateBinding Value, Mode=TwoWay}"
@@ -82,7 +90,7 @@
                   </RepeatButton>
                 </Track.IncreaseButton>
                 <Thumb Name="ColorSliderThumb"
-                       Theme="{StaticResource ColorSliderThumbTheme}"
+                       Theme="{DynamicResource ColorSliderThumbTheme}"
                        Margin="0"
                        Padding="0"
                        DataContext="{TemplateBinding Value}"
@@ -97,26 +105,27 @@
 
     <Style Selector="^:vertical">
       <Setter Property="BorderThickness" Value="0" />
-      <Setter Property="CornerRadius" Value="10" />
-      <Setter Property="Width" Value="20" />
+      <Setter Property="CornerRadius" Value="{DynamicResource ColorSliderCornerRadius}" />
+      <Setter Property="Width" Value="{DynamicResource ColorSliderSize}" />
       <Setter Property="Template">
         <ControlTemplate TargetType="{x:Type ColorSlider}">
           <Border BorderThickness="{TemplateBinding BorderThickness}"
                   BorderBrush="{TemplateBinding BorderBrush}"
                   CornerRadius="{TemplateBinding CornerRadius}">
             <Grid Margin="{TemplateBinding Padding}">
-              <Rectangle HorizontalAlignment="Stretch"
-                         VerticalAlignment="Stretch"
-                         Fill="{StaticResource ColorControlCheckeredBackgroundBrush}"
-                         RadiusX="{TemplateBinding CornerRadius, Converter={StaticResource TopLeftCornerRadiusConverter}}"
-                         RadiusY="{TemplateBinding CornerRadius, Converter={StaticResource BottomRightCornerRadiusConverter}}" />
-              <Rectangle HorizontalAlignment="Stretch"
-                         VerticalAlignment="Stretch"
-                         Fill="{TemplateBinding Background}"
-                         RadiusX="{TemplateBinding CornerRadius, Converter={StaticResource TopLeftCornerRadiusConverter}}"
-                         RadiusY="{TemplateBinding CornerRadius, Converter={StaticResource BottomRightCornerRadiusConverter}}" />
+              <Border HorizontalAlignment="Center"
+                      VerticalAlignment="Stretch"
+                      Width="{Binding ElementName=PART_Track, Path=Bounds.Width}"
+                      Background="{StaticResource ColorControlCheckeredBackgroundBrush}"
+                      CornerRadius="{DynamicResource ColorSliderTrackCornerRadius}" />
+              <Border HorizontalAlignment="Center"
+                      VerticalAlignment="Stretch"
+                      Width="{Binding ElementName=PART_Track, Path=Bounds.Width}"
+                      Background="{TemplateBinding Background}"
+                      CornerRadius="{DynamicResource ColorSliderTrackCornerRadius}" />
               <Track Name="PART_Track"
-                     HorizontalAlignment="Stretch"
+                     Width="{DynamicResource ColorSliderTrackSize}"
+                     HorizontalAlignment="Center"
                      VerticalAlignment="Stretch"
                      Minimum="{TemplateBinding Minimum}"
                      Maximum="{TemplateBinding Maximum}"
@@ -154,7 +163,7 @@
                   </RepeatButton>
                 </Track.IncreaseButton>
                 <Thumb Name="ColorSliderThumb"
-                       Theme="{StaticResource ColorSliderThumbTheme}"
+                       Theme="{DynamicResource ColorSliderThumbTheme}"
                        Margin="0"
                        Padding="0"
                        DataContext="{TemplateBinding Value}"
diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorSlider.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorSlider.xaml
index e9d12499f9..472f1ca100 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorSlider.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Simple/ColorSlider.xaml
@@ -1,13 +1,20 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
 
+  <!-- Note that the Slider thumb should generally follow the overall Slider dimensions.
+       Therefore, there are not currently separate resources to control it. -->
+  <x:Double x:Key="ColorSliderSize">20</x:Double>
+  <x:Double x:Key="ColorSliderTrackSize">20</x:Double>
+  <CornerRadius x:Key="ColorSliderCornerRadius">10</CornerRadius>
+  <CornerRadius x:Key="ColorSliderTrackCornerRadius">10</CornerRadius>
+
   <ControlTheme x:Key="ColorSliderThumbTheme"
                 TargetType="Thumb">
     <Setter Property="Background" Value="Transparent" />
     <Setter Property="BorderBrush" Value="{DynamicResource ThemeForegroundBrush}" />
     <!--TODO: <Setter Property="BorderBrush" Value="{DynamicResource ColorControlDefaultSelectorBrush}" />-->
     <Setter Property="BorderThickness" Value="3" />
-    <Setter Property="CornerRadius" Value="10" />
+    <Setter Property="CornerRadius" Value="{DynamicResource ColorSliderCornerRadius}" />
     <Setter Property="Template">
       <Setter.Value>
         <ControlTemplate>
@@ -25,27 +32,28 @@
 
     <Style Selector="^:horizontal">
       <Setter Property="BorderThickness" Value="0" />
-      <Setter Property="CornerRadius" Value="10" />
-      <Setter Property="Height" Value="20" />
+      <Setter Property="CornerRadius" Value="{DynamicResource ColorSliderCornerRadius}" />
+      <Setter Property="Height" Value="{DynamicResource ColorSliderSize}" />
       <Setter Property="Template">
         <ControlTemplate TargetType="{x:Type ColorSlider}">
           <Border BorderThickness="{TemplateBinding BorderThickness}"
                   BorderBrush="{TemplateBinding BorderBrush}"
                   CornerRadius="{TemplateBinding CornerRadius}">
             <Grid Margin="{TemplateBinding Padding}">
-              <Rectangle HorizontalAlignment="Stretch"
-                         VerticalAlignment="Stretch"
-                         Fill="{StaticResource ColorControlCheckeredBackgroundBrush}"
-                         RadiusX="{TemplateBinding CornerRadius, Converter={StaticResource TopLeftCornerRadiusConverter}}"
-                         RadiusY="{TemplateBinding CornerRadius, Converter={StaticResource BottomRightCornerRadiusConverter}}" />
-              <Rectangle HorizontalAlignment="Stretch"
-                         VerticalAlignment="Stretch"
-                         Fill="{TemplateBinding Background}"
-                         RadiusX="{TemplateBinding CornerRadius, Converter={StaticResource TopLeftCornerRadiusConverter}}"
-                         RadiusY="{TemplateBinding CornerRadius, Converter={StaticResource BottomRightCornerRadiusConverter}}" />
+              <Border HorizontalAlignment="Stretch"
+                      VerticalAlignment="Center"
+                      Height="{Binding ElementName=PART_Track, Path=Bounds.Height}"
+                      Background="{StaticResource ColorControlCheckeredBackgroundBrush}"
+                      CornerRadius="{DynamicResource ColorSliderTrackCornerRadius}" />
+              <Border HorizontalAlignment="Stretch"
+                      VerticalAlignment="Center"
+                      Height="{Binding ElementName=PART_Track, Path=Bounds.Height}"
+                      Background="{TemplateBinding Background}"
+                      CornerRadius="{DynamicResource ColorSliderTrackCornerRadius}" />
               <Track Name="PART_Track"
+                     Height="{DynamicResource ColorSliderTrackSize}"
                      HorizontalAlignment="Stretch"
-                     VerticalAlignment="Stretch"
+                     VerticalAlignment="Center"
                      Minimum="{TemplateBinding Minimum}"
                      Maximum="{TemplateBinding Maximum}"
                      Value="{TemplateBinding Value, Mode=TwoWay}"
@@ -82,7 +90,7 @@
                   </RepeatButton>
                 </Track.IncreaseButton>
                 <Thumb Name="ColorSliderThumb"
-                       Theme="{StaticResource ColorSliderThumbTheme}"
+                       Theme="{DynamicResource ColorSliderThumbTheme}"
                        Margin="0"
                        Padding="0"
                        DataContext="{TemplateBinding Value}"
@@ -97,26 +105,27 @@
 
     <Style Selector="^:vertical">
       <Setter Property="BorderThickness" Value="0" />
-      <Setter Property="CornerRadius" Value="10" />
-      <Setter Property="Width" Value="20" />
+      <Setter Property="CornerRadius" Value="{DynamicResource ColorSliderCornerRadius}" />
+      <Setter Property="Width" Value="{DynamicResource ColorSliderSize}" />
       <Setter Property="Template">
         <ControlTemplate TargetType="{x:Type ColorSlider}">
           <Border BorderThickness="{TemplateBinding BorderThickness}"
                   BorderBrush="{TemplateBinding BorderBrush}"
                   CornerRadius="{TemplateBinding CornerRadius}">
             <Grid Margin="{TemplateBinding Padding}">
-              <Rectangle HorizontalAlignment="Stretch"
-                         VerticalAlignment="Stretch"
-                         Fill="{StaticResource ColorControlCheckeredBackgroundBrush}"
-                         RadiusX="{TemplateBinding CornerRadius, Converter={StaticResource TopLeftCornerRadiusConverter}}"
-                         RadiusY="{TemplateBinding CornerRadius, Converter={StaticResource BottomRightCornerRadiusConverter}}" />
-              <Rectangle HorizontalAlignment="Stretch"
-                         VerticalAlignment="Stretch"
-                         Fill="{TemplateBinding Background}"
-                         RadiusX="{TemplateBinding CornerRadius, Converter={StaticResource TopLeftCornerRadiusConverter}}"
-                         RadiusY="{TemplateBinding CornerRadius, Converter={StaticResource BottomRightCornerRadiusConverter}}" />
+              <Border HorizontalAlignment="Center"
+                      VerticalAlignment="Stretch"
+                      Width="{Binding ElementName=PART_Track, Path=Bounds.Width}"
+                      Background="{StaticResource ColorControlCheckeredBackgroundBrush}"
+                      CornerRadius="{DynamicResource ColorSliderTrackCornerRadius}" />
+              <Border HorizontalAlignment="Center"
+                      VerticalAlignment="Stretch"
+                      Width="{Binding ElementName=PART_Track, Path=Bounds.Width}"
+                      Background="{TemplateBinding Background}"
+                      CornerRadius="{DynamicResource ColorSliderTrackCornerRadius}" />
               <Track Name="PART_Track"
-                     HorizontalAlignment="Stretch"
+                     Width="{DynamicResource ColorSliderTrackSize}"
+                     HorizontalAlignment="Center"
                      VerticalAlignment="Stretch"
                      Minimum="{TemplateBinding Minimum}"
                      Maximum="{TemplateBinding Maximum}"
@@ -154,7 +163,7 @@
                   </RepeatButton>
                 </Track.IncreaseButton>
                 <Thumb Name="ColorSliderThumb"
-                       Theme="{StaticResource ColorSliderThumbTheme}"
+                       Theme="{DynamicResource ColorSliderThumbTheme}"
                        Margin="0"
                        Padding="0"
                        DataContext="{TemplateBinding Value}"

From 849d801429f694312d89077b7ba0eec41bfa7f36 Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sun, 19 Mar 2023 12:41:29 -0400
Subject: [PATCH 12/40] Add custom ColorSliderThumbTheme to the sample page

This theme makes the thumb larger than the track
---
 .../ControlCatalog/Pages/ColorPickerPage.xaml | 35 +++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/samples/ControlCatalog/Pages/ColorPickerPage.xaml b/samples/ControlCatalog/Pages/ColorPickerPage.xaml
index 649256ba83..b759720cf2 100644
--- a/samples/ControlCatalog/Pages/ColorPickerPage.xaml
+++ b/samples/ControlCatalog/Pages/ColorPickerPage.xaml
@@ -28,6 +28,41 @@
     <Grid Grid.Column="2"
           Grid.Row="0"
           RowDefinitions="Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto">
+      <Grid.Resources>
+
+        <x:Double x:Key="ColorSliderSize">24</x:Double>
+        <x:Double x:Key="ColorSliderTrackSize">18</x:Double>
+        <CornerRadius x:Key="ColorSliderCornerRadius">12</CornerRadius>
+        <CornerRadius x:Key="ColorSliderTrackCornerRadius">9</CornerRadius>
+
+        <!-- Due to 'SystemControlForegroundBaseHighBrush' usage this only works in Fluent theme. -->
+        <!-- Otherwise it would be necessary to make custom light/dark resources. -->
+        <ControlTheme x:Key="ColorSliderThumbTheme"
+                      TargetType="Thumb">
+          <Setter Property="Background" Value="Transparent" />
+          <Setter Property="BorderBrush" Value="{DynamicResource SystemControlForegroundBaseHighBrush}" />
+          <Setter Property="BorderThickness" Value="5" />
+          <Setter Property="CornerRadius" Value="{DynamicResource ColorSliderCornerRadius}" />
+          <Setter Property="Template">
+            <Setter.Value>
+              <ControlTemplate>
+                <Grid>
+                  <Border Background="{TemplateBinding Background}"
+                          BorderBrush="{TemplateBinding BorderBrush}"
+                          BorderThickness="{TemplateBinding BorderThickness}"
+                          CornerRadius="{TemplateBinding CornerRadius}" />
+                  <Ellipse Height="{TemplateBinding Height}"
+                           Width="{TemplateBinding Width}"
+                           Fill="Transparent"
+                           Stroke="{TemplateBinding Foreground}"
+                           StrokeThickness="1" />
+                </Grid>
+              </ControlTemplate>
+            </Setter.Value>
+          </Setter>
+        </ControlTheme>
+
+      </Grid.Resources>
       <ColorSpectrum x:Name="ColorSpectrum1"
                      Grid.Row="0"
                      Color="Red"

From 818b45320f6ca740fe59f59578cfbc571c974159 Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sun, 19 Mar 2023 12:41:47 -0400
Subject: [PATCH 13/40] Fix ColorHelper CI build error

---
 src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs b/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs
index 7fa2dfdddd..c9801c432b 100644
--- a/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs
+++ b/src/Avalonia.Controls.ColorPicker/Helpers/ColorHelper.cs
@@ -170,7 +170,7 @@ namespace Avalonia.Controls.Primitives
             // Cache results for next time as well
             if (closestKnownColor != KnownColor.None)
             {
-                string displayName;
+                string? displayName;
 
                 lock (_knownColorCacheMutex)
                 {

From 10d41eaeee6bf2ae9822905c45746a9ef0730643 Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sun, 19 Mar 2023 18:00:31 -0400
Subject: [PATCH 14/40] Switch AutoCompleteBox to using StyledProperty where
 possible

---
 .../AutoCompleteBox.Properties.cs             | 104 ++++++++----------
 .../AutoCompleteBox/AutoCompleteBox.cs        |  65 +++++------
 2 files changed, 75 insertions(+), 94 deletions(-)

diff --git a/src/Avalonia.Controls/AutoCompleteBox/AutoCompleteBox.Properties.cs b/src/Avalonia.Controls/AutoCompleteBox/AutoCompleteBox.Properties.cs
index 93b057e176..b38151854b 100644
--- a/src/Avalonia.Controls/AutoCompleteBox/AutoCompleteBox.Properties.cs
+++ b/src/Avalonia.Controls/AutoCompleteBox/AutoCompleteBox.Properties.cs
@@ -52,34 +52,32 @@ namespace Avalonia.Controls
         /// </summary>
         /// <value>The identifier for the <see cref="IsTextCompletionEnabled" /> property.</value>
         public static readonly StyledProperty<bool> IsTextCompletionEnabledProperty =
-            AvaloniaProperty.Register<AutoCompleteBox, bool>(nameof(IsTextCompletionEnabled));
+            AvaloniaProperty.Register<AutoCompleteBox, bool>(
+                nameof(IsTextCompletionEnabled));
 
         /// <summary>
         /// Identifies the <see cref="ItemTemplate" /> property.
         /// </summary>
         /// <value>The identifier for the <see cref="ItemTemplate" /> property.</value>
         public static readonly StyledProperty<IDataTemplate> ItemTemplateProperty =
-            AvaloniaProperty.Register<AutoCompleteBox, IDataTemplate>(nameof(ItemTemplate));
+            AvaloniaProperty.Register<AutoCompleteBox, IDataTemplate>(
+                nameof(ItemTemplate));
 
         /// <summary>
         /// Identifies the <see cref="IsDropDownOpen" /> property.
         /// </summary>
         /// <value>The identifier for the <see cref="IsDropDownOpen" /> property.</value>
-        public static readonly DirectProperty<AutoCompleteBox, bool> IsDropDownOpenProperty =
-            AvaloniaProperty.RegisterDirect<AutoCompleteBox, bool>(
-                nameof(IsDropDownOpen),
-                o => o.IsDropDownOpen,
-                (o, v) => o.IsDropDownOpen = v);
+        public static readonly StyledProperty<bool> IsDropDownOpenProperty =
+            AvaloniaProperty.Register<AutoCompleteBox, bool>(
+                nameof(IsDropDownOpen));
 
         /// <summary>
         /// Identifies the <see cref="SelectedItem" /> property.
         /// </summary>
         /// <value>The identifier the <see cref="SelectedItem" /> property.</value>
-        public static readonly DirectProperty<AutoCompleteBox, object?> SelectedItemProperty =
-            AvaloniaProperty.RegisterDirect<AutoCompleteBox, object?>(
+        public static readonly StyledProperty<object?> SelectedItemProperty =
+            AvaloniaProperty.Register<AutoCompleteBox, object?>(
                 nameof(SelectedItem),
-                o => o.SelectedItem,
-                (o, v) => o.SelectedItem = v,
                 defaultBindingMode: BindingMode.TwoWay,
                 enableDataValidation: true);
 
@@ -115,58 +113,50 @@ namespace Avalonia.Controls
         /// Identifies the <see cref="ItemFilter" /> property.
         /// </summary>
         /// <value>The identifier for the <see cref="ItemFilter" /> property.</value>
-        public static readonly DirectProperty<AutoCompleteBox, AutoCompleteFilterPredicate<object?>?> ItemFilterProperty =
-            AvaloniaProperty.RegisterDirect<AutoCompleteBox, AutoCompleteFilterPredicate<object?>?>(
-                nameof(ItemFilter),
-                o => o.ItemFilter,
-                (o, v) => o.ItemFilter = v);
+        public static readonly StyledProperty<AutoCompleteFilterPredicate<object?>?> ItemFilterProperty =
+            AvaloniaProperty.Register<AutoCompleteBox, AutoCompleteFilterPredicate<object?>?>(
+                nameof(ItemFilter));
 
         /// <summary>
         /// Identifies the <see cref="TextFilter" /> property.
         /// </summary>
         /// <value>The identifier for the <see cref="TextFilter" /> property.</value>
-        public static readonly DirectProperty<AutoCompleteBox, AutoCompleteFilterPredicate<string?>?> TextFilterProperty =
-            AvaloniaProperty.RegisterDirect<AutoCompleteBox, AutoCompleteFilterPredicate<string?>?>(
+        public static readonly StyledProperty<AutoCompleteFilterPredicate<string?>?> TextFilterProperty =
+            AvaloniaProperty.Register<AutoCompleteBox, AutoCompleteFilterPredicate<string?>?>(
                 nameof(TextFilter),
-                o => o.TextFilter,
-                (o, v) => o.TextFilter = v,
-                unsetValue: AutoCompleteSearch.GetFilter(AutoCompleteFilterMode.StartsWith));
+                defaultValue: AutoCompleteSearch.GetFilter(AutoCompleteFilterMode.StartsWith));
 
         /// <summary>
         /// Identifies the <see cref="ItemSelector" /> property.
         /// </summary>
         /// <value>The identifier for the <see cref="ItemSelector" /> property.</value>
-        public static readonly DirectProperty<AutoCompleteBox, AutoCompleteSelector<object>?> ItemSelectorProperty =
-            AvaloniaProperty.RegisterDirect<AutoCompleteBox, AutoCompleteSelector<object>?>(
-                nameof(ItemSelector),
-                o => o.ItemSelector,
-                (o, v) => o.ItemSelector = v);
+        public static readonly StyledProperty<AutoCompleteSelector<object>?> ItemSelectorProperty =
+            AvaloniaProperty.Register<AutoCompleteBox, AutoCompleteSelector<object>?>(
+                nameof(ItemSelector));
 
         /// <summary>
         /// Identifies the <see cref="TextSelector" /> property.
         /// </summary>
         /// <value>The identifier for the <see cref="TextSelector" /> property.</value>
-        public static readonly DirectProperty<AutoCompleteBox, AutoCompleteSelector<string?>?> TextSelectorProperty =
-            AvaloniaProperty.RegisterDirect<AutoCompleteBox, AutoCompleteSelector<string?>?>(
-                nameof(TextSelector),
-                o => o.TextSelector,
-                (o, v) => o.TextSelector = v);
+        public static readonly StyledProperty<AutoCompleteSelector<string?>?> TextSelectorProperty =
+            AvaloniaProperty.Register<AutoCompleteBox, AutoCompleteSelector<string?>?>(
+                nameof(TextSelector));
 
         /// <summary>
         /// Identifies the <see cref="Items" /> property.
         /// </summary>
         /// <value>The identifier for the <see cref="Items" /> property.</value>
-        public static readonly DirectProperty<AutoCompleteBox, IEnumerable?> ItemsProperty =
-            AvaloniaProperty.RegisterDirect<AutoCompleteBox, IEnumerable?>(
-                nameof(Items),
-                o => o.Items,
-                (o, v) => o.Items = v);
+        public static readonly StyledProperty<IEnumerable?> ItemsProperty =
+            AvaloniaProperty.Register<AutoCompleteBox, IEnumerable?>(
+                nameof(Items));
 
-        public static readonly DirectProperty<AutoCompleteBox, Func<string?, CancellationToken, Task<IEnumerable<object>>>?> AsyncPopulatorProperty =
-            AvaloniaProperty.RegisterDirect<AutoCompleteBox, Func<string?, CancellationToken, Task<IEnumerable<object>>>?>(
-                nameof(AsyncPopulator),
-                o => o.AsyncPopulator,
-                (o, v) => o.AsyncPopulator = v);
+        /// <summary>
+        /// Identifies the <see cref="AsyncPopulator" /> property.
+        /// </summary>
+        /// <value>The identifier for the <see cref="AsyncPopulator" /> property.</value>
+        public static readonly StyledProperty<Func<string?, CancellationToken, Task<IEnumerable<object>>>?> AsyncPopulatorProperty =
+            AvaloniaProperty.Register<AutoCompleteBox, Func<string?, CancellationToken, Task<IEnumerable<object>>>?>(
+                nameof(AsyncPopulator));
 
         /// <summary>
         /// Gets or sets the minimum number of characters required to be entered
@@ -265,8 +255,8 @@ namespace Avalonia.Controls
         /// </value>
         public bool IsDropDownOpen
         {
-            get => _isDropDownOpen;
-            set => SetAndRaise(IsDropDownOpenProperty, ref  _isDropDownOpen, value);
+            get => GetValue(IsDropDownOpenProperty);
+            set => SetValue(IsDropDownOpenProperty, value);
         }
 
         /// <summary>
@@ -303,8 +293,8 @@ namespace Avalonia.Controls
         /// </remarks>
         public object? SelectedItem
         {
-            get => _selectedItem;
-            set => SetAndRaise(SelectedItemProperty, ref _selectedItem, value);
+            get => GetValue(SelectedItemProperty);
+            set => SetValue(SelectedItemProperty, value);
         }
 
         /// <summary>
@@ -388,8 +378,8 @@ namespace Avalonia.Controls
         /// </remarks>
         public AutoCompleteFilterPredicate<object?>? ItemFilter
         {
-            get => _itemFilter;
-            set => SetAndRaise(ItemFilterProperty, ref _itemFilter, value);
+            get => GetValue(ItemFilterProperty);
+            set => SetValue(ItemFilterProperty, value);
         }
 
         /// <summary>
@@ -406,8 +396,8 @@ namespace Avalonia.Controls
         /// </remarks>
         public AutoCompleteFilterPredicate<string?>? TextFilter
         {
-            get => _textFilter;
-            set => SetAndRaise(TextFilterProperty, ref _textFilter, value);
+            get => GetValue(TextFilterProperty);
+            set => SetValue(TextFilterProperty, value);
         }
 
         /// <summary>
@@ -420,8 +410,8 @@ namespace Avalonia.Controls
         /// </value>
         public AutoCompleteSelector<object>? ItemSelector
         {
-            get => _itemSelector;
-            set => SetAndRaise(ItemSelectorProperty, ref _itemSelector, value);
+            get => GetValue(ItemSelectorProperty);
+            set => SetValue(ItemSelectorProperty, value);
         }
 
         /// <summary>
@@ -436,14 +426,14 @@ namespace Avalonia.Controls
         /// </value>
         public AutoCompleteSelector<string?>? TextSelector
         {
-            get => _textSelector;
-            set => SetAndRaise(TextSelectorProperty, ref _textSelector, value);
+            get => GetValue(TextSelectorProperty);
+            set => SetValue(TextSelectorProperty, value);
         }
 
         public Func<string?, CancellationToken, Task<IEnumerable<object>>>? AsyncPopulator
         {
-            get => _asyncPopulator;
-            set => SetAndRaise(AsyncPopulatorProperty, ref _asyncPopulator, value);
+            get => GetValue(AsyncPopulatorProperty);
+            set => SetValue(AsyncPopulatorProperty, value);
         }
 
         /// <summary>
@@ -454,8 +444,8 @@ namespace Avalonia.Controls
         /// drop-down portion of the <see cref="AutoCompleteBox" /> control.</value>
         public IEnumerable? Items
         {
-            get => _itemsEnumerable;
-            set => SetAndRaise(ItemsProperty, ref _itemsEnumerable, value);
+            get => GetValue(ItemsProperty);
+            set => SetValue(ItemsProperty, value);
         }
     }
 }
diff --git a/src/Avalonia.Controls/AutoCompleteBox/AutoCompleteBox.cs b/src/Avalonia.Controls/AutoCompleteBox/AutoCompleteBox.cs
index 2d074ef7fa..72a23144cf 100644
--- a/src/Avalonia.Controls/AutoCompleteBox/AutoCompleteBox.cs
+++ b/src/Avalonia.Controls/AutoCompleteBox/AutoCompleteBox.cs
@@ -94,8 +94,6 @@ namespace Avalonia.Controls
         /// </summary>
         private const string ElementTextBox = "PART_TextBox";
 
-        private IEnumerable? _itemsEnumerable;
-
         /// <summary>
         /// Gets or sets a local cached copy of the items data.
         /// </summary>
@@ -188,24 +186,15 @@ namespace Avalonia.Controls
         /// </summary>
         private IDisposable? _collectionChangeSubscription;
 
-        private Func<string?, CancellationToken, Task<IEnumerable<object>>>? _asyncPopulator;
         private CancellationTokenSource? _populationCancellationTokenSource;
 
         private bool _itemTemplateIsFromValueMemberBinding = true;
         private bool _settingItemTemplateFromValueMemberBinding;
 
-        private object? _selectedItem;
-        private bool _isDropDownOpen;
         private bool _isFocused = false;
 
         private string? _searchText = string.Empty;
 
-        private AutoCompleteFilterPredicate<object?>? _itemFilter;
-        private AutoCompleteFilterPredicate<string?>? _textFilter = AutoCompleteSearch.GetFilter(AutoCompleteFilterMode.StartsWith);
-
-        private AutoCompleteSelector<object>? _itemSelector;
-        private AutoCompleteSelector<string?>? _textSelector;
-
         private readonly EventHandler _populateDropDownHandler;
 
         /// <summary>
@@ -264,7 +253,7 @@ namespace Avalonia.Controls
             bool isEnabled = (bool)e.NewValue!;
             if (!isEnabled)
             {
-                IsDropDownOpen = false;
+                SetCurrentValue(IsDropDownOpenProperty, false);
             }
         }
 
@@ -388,7 +377,7 @@ namespace Avalonia.Controls
             {
                 // Reset the old value before it was incorrectly written
                 _ignorePropertyChange = true;
-                SetValue(e.Property, e.OldValue);
+                SetCurrentValue(e.Property, e.OldValue);
 
                 throw new InvalidOperationException("Cannot set read-only property SearchText.");
             }
@@ -403,7 +392,7 @@ namespace Avalonia.Controls
             AutoCompleteFilterMode mode = (AutoCompleteFilterMode)e.NewValue!;
 
             // Sets the filter predicate for the new value
-            TextFilter = AutoCompleteSearch.GetFilter(mode);
+            SetCurrentValue(TextFilterProperty, AutoCompleteSearch.GetFilter(mode));
         }
 
         /// <summary>
@@ -417,12 +406,12 @@ namespace Avalonia.Controls
             // If null, revert to the "None" predicate
             if (value == null)
             {
-                FilterMode = AutoCompleteFilterMode.None;
+                SetCurrentValue(FilterModeProperty, AutoCompleteFilterMode.None);
             }
             else
             {
-                FilterMode = AutoCompleteFilterMode.Custom;
-                TextFilter = null;
+                SetCurrentValue(FilterModeProperty, AutoCompleteFilterMode.Custom);
+                SetCurrentValue(TextFilterProperty, null);
             }
         }
 
@@ -442,7 +431,7 @@ namespace Avalonia.Controls
         }
         private void OnValueMemberBindingChanged(IBinding? value)
         {
-            if(_itemTemplateIsFromValueMemberBinding)
+            if (_itemTemplateIsFromValueMemberBinding)
             {
                 var template =
                     new FuncDataTemplate(
@@ -456,7 +445,7 @@ namespace Avalonia.Controls
                         });
 
                 _settingItemTemplateFromValueMemberBinding = true;
-                ItemTemplate = template;
+                SetCurrentValue(ItemTemplateProperty, template);
                 _settingItemTemplateFromValueMemberBinding = false;
             }
         }
@@ -713,7 +702,7 @@ namespace Avalonia.Controls
                 // The drop down is not open, the Down key will toggle it open.
                 if (e.Key == Key.Down)
                 {
-                    IsDropDownOpen = true;
+                    SetCurrentValue(IsDropDownOpenProperty, true);
                     e.Handled = true;
                 }
             }
@@ -722,7 +711,7 @@ namespace Avalonia.Controls
             switch (e.Key)
             {
                 case Key.F4:
-                    IsDropDownOpen = !IsDropDownOpen;
+                    SetCurrentValue(IsDropDownOpenProperty, !IsDropDownOpen);
                     e.Handled = true;
                     break;
 
@@ -827,7 +816,7 @@ namespace Avalonia.Controls
             }
             else
             {
-                IsDropDownOpen = false;
+                SetCurrentValue(IsDropDownOpenProperty, false);
                 _userCalledPopulate = false;
                 ClearTextBoxSelection();
             }
@@ -1021,7 +1010,7 @@ namespace Avalonia.Controls
             if (args.Cancel)
             {
                 _ignorePropertyChange = true;
-                SetValue(IsDropDownOpenProperty, oldValue);
+                SetCurrentValue(IsDropDownOpenProperty, oldValue);
             }
             else
             {
@@ -1046,7 +1035,7 @@ namespace Avalonia.Controls
             if (args.Cancel)
             {
                 _ignorePropertyChange = true;
-                SetValue(IsDropDownOpenProperty, oldValue);
+                SetCurrentValue(IsDropDownOpenProperty, oldValue);
             }
             else
             {
@@ -1066,7 +1055,7 @@ namespace Avalonia.Controls
             // Force the drop down dependency property to be false.
             if (IsDropDownOpen)
             {
-                IsDropDownOpen = false;
+                SetCurrentValue(IsDropDownOpenProperty, false);
             }
 
             // Fire the DropDownClosed event
@@ -1088,7 +1077,7 @@ namespace Avalonia.Controls
             // Update the prefix/search text.
             SearchText = Text;
 
-            if(TryPopulateAsync(SearchText))
+            if (TryPopulateAsync(SearchText))
             {
                 return;
             }
@@ -1110,7 +1099,7 @@ namespace Avalonia.Controls
             _populationCancellationTokenSource?.Dispose();
             _populationCancellationTokenSource = null;
 
-            if(_asyncPopulator == null)
+            if (AsyncPopulator == null)
             {
                 return false;
             }
@@ -1127,7 +1116,7 @@ namespace Avalonia.Controls
 
             try
             {
-                IEnumerable<object> result = await _asyncPopulator!.Invoke(searchText, cancellationToken);
+                IEnumerable<object> result = await AsyncPopulator!.Invoke(searchText, cancellationToken);
                 var resultList = result.ToList();
 
                 if (cancellationToken.IsCancellationRequested)
@@ -1139,7 +1128,7 @@ namespace Avalonia.Controls
                 {
                     if (!cancellationToken.IsCancellationRequested)
                     {
-                        Items = resultList;
+                        SetCurrentValue(ItemsProperty, resultList);
                         PopulateComplete();
                     }
                 });
@@ -1199,7 +1188,7 @@ namespace Avalonia.Controls
         private string? FormatValue(object? value, bool clearDataContext)
         {
             string? result = FormatValue(value);
-            if(clearDataContext && _valueBindingEvaluator != null)
+            if (clearDataContext && _valueBindingEvaluator != null)
             {
                 _valueBindingEvaluator.ClearDataContext();
             }
@@ -1332,7 +1321,7 @@ namespace Avalonia.Controls
             // 1. Minimum prefix length
             // 2. If a delay timer is in use, use it
             bool populateReady = newText.Length >= MinimumPrefixLength && MinimumPrefixLength >= 0;
-            if(populateReady && MinimumPrefixLength == 0 && String.IsNullOrEmpty(newText) && String.IsNullOrEmpty(SearchText))
+            if (populateReady && MinimumPrefixLength == 0 && String.IsNullOrEmpty(newText) && String.IsNullOrEmpty(SearchText))
             {
                 populateReady = false;
             }
@@ -1361,10 +1350,12 @@ namespace Avalonia.Controls
                 {
                     _skipSelectedItemTextUpdate = true;
                 }
-                SelectedItem = null;
+
+                SetCurrentValue(SelectedItemProperty, null);
+
                 if (IsDropDownOpen)
                 {
-                    IsDropDownOpen = false;
+                    SetCurrentValue(IsDropDownOpenProperty, false);
                 }
             }
         }
@@ -1600,7 +1591,7 @@ namespace Avalonia.Controls
             if (isDropDownOpen != IsDropDownOpen)
             {
                 _ignorePropertyChange = true;
-                IsDropDownOpen = isDropDownOpen;
+                SetCurrentValue(IsDropDownOpenProperty, isDropDownOpen);
             }
             if (IsDropDownOpen)
             {
@@ -1688,7 +1679,7 @@ namespace Avalonia.Controls
             {
                 _skipSelectedItemTextUpdate = true;
             }
-            SelectedItem = newSelectedItem;
+            SetCurrentValue(SelectedItemProperty, newSelectedItem);
 
             // Restore updates for TextSelection
             if (_ignoreTextSelectionChange)
@@ -1784,7 +1775,7 @@ namespace Avalonia.Controls
         /// <param name="e">The selection changed event data.</param>
         private void OnAdapterSelectionChanged(object? sender, SelectionChangedEventArgs e)
         {
-            SelectedItem = _adapter!.SelectedItem;
+            SetCurrentValue(SelectedItemProperty, _adapter!.SelectedItem);
         }
 
         //TODO Check UpdateTextCompletion
@@ -1795,7 +1786,7 @@ namespace Avalonia.Controls
         /// <param name="e">The event data.</param>
         private void OnAdapterSelectionComplete(object? sender, RoutedEventArgs e)
         {
-            IsDropDownOpen = false;
+            SetCurrentValue(IsDropDownOpenProperty, false);
 
             // Completion will update the selected value
             //UpdateTextCompletion(false);

From 46f38f42af8d21d89e4206d17efb72f93fa29516 Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Sun, 19 Mar 2023 18:03:00 -0400
Subject: [PATCH 15/40] Fix comments with incorrect property reference

---
 src/Avalonia.Base/Layout/Layoutable.cs                          | 2 +-
 src/Avalonia.Base/Visual.cs                                     | 2 +-
 src/Avalonia.Controls.ItemsRepeater/Layout/UniformGridLayout.cs | 2 +-
 src/Avalonia.Controls/Primitives/ScrollBar.cs                   | 2 +-
 src/Avalonia.Controls/ScrollViewer.cs                           | 2 +-
 src/Avalonia.Controls/Slider.cs                                 | 2 +-
 src/Avalonia.Controls/TopLevel.cs                               | 2 +-
 7 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/Avalonia.Base/Layout/Layoutable.cs b/src/Avalonia.Base/Layout/Layoutable.cs
index ea84dc84bd..ed88b73149 100644
--- a/src/Avalonia.Base/Layout/Layoutable.cs
+++ b/src/Avalonia.Base/Layout/Layoutable.cs
@@ -125,7 +125,7 @@ namespace Avalonia.Layout
             AvaloniaProperty.Register<Layoutable, VerticalAlignment>(nameof(VerticalAlignment));
 
         /// <summary>
-        /// Defines the <see cref="UseLayoutRoundingProperty"/> property.
+        /// Defines the <see cref="UseLayoutRounding"/> property.
         /// </summary>
         public static readonly StyledProperty<bool> UseLayoutRoundingProperty =
             AvaloniaProperty.Register<Layoutable, bool>(nameof(UseLayoutRounding), defaultValue: true, inherits: true);
diff --git a/src/Avalonia.Base/Visual.cs b/src/Avalonia.Base/Visual.cs
index df0c5b100f..b4c5b2a1d2 100644
--- a/src/Avalonia.Base/Visual.cs
+++ b/src/Avalonia.Base/Visual.cs
@@ -50,7 +50,7 @@ namespace Avalonia
             AvaloniaProperty.Register<Visual, Geometry?>(nameof(Clip));
 
         /// <summary>
-        /// Defines the <see cref="IsVisibleProperty"/> property.
+        /// Defines the <see cref="IsVisible"/> property.
         /// </summary>
         public static readonly StyledProperty<bool> IsVisibleProperty =
             AvaloniaProperty.Register<Visual, bool>(nameof(IsVisible), true);
diff --git a/src/Avalonia.Controls.ItemsRepeater/Layout/UniformGridLayout.cs b/src/Avalonia.Controls.ItemsRepeater/Layout/UniformGridLayout.cs
index c539396e75..7701513455 100644
--- a/src/Avalonia.Controls.ItemsRepeater/Layout/UniformGridLayout.cs
+++ b/src/Avalonia.Controls.ItemsRepeater/Layout/UniformGridLayout.cs
@@ -113,7 +113,7 @@ namespace Avalonia.Layout
             AvaloniaProperty.Register<UniformGridLayout, double>(nameof(MinRowSpacing));
 
         /// <summary>
-        /// Defines the <see cref="MaximumRowsOrColumnsProperty"/> property.
+        /// Defines the <see cref="MaximumRowsOrColumns"/> property.
         /// </summary>
         public static readonly StyledProperty<int> MaximumRowsOrColumnsProperty =
             AvaloniaProperty.Register<UniformGridLayout, int>(nameof(MaximumRowsOrColumns));
diff --git a/src/Avalonia.Controls/Primitives/ScrollBar.cs b/src/Avalonia.Controls/Primitives/ScrollBar.cs
index 8b2321e40b..b4a8408901 100644
--- a/src/Avalonia.Controls/Primitives/ScrollBar.cs
+++ b/src/Avalonia.Controls/Primitives/ScrollBar.cs
@@ -49,7 +49,7 @@ namespace Avalonia.Controls.Primitives
             AvaloniaProperty.Register<ScrollBar, Orientation>(nameof(Orientation), Orientation.Vertical);
 
         /// <summary>
-        /// Defines the <see cref="IsExpandedProperty"/> property.
+        /// Defines the <see cref="IsExpanded"/> property.
         /// </summary>
         public static readonly DirectProperty<ScrollBar, bool> IsExpandedProperty =
             AvaloniaProperty.RegisterDirect<ScrollBar, bool>(
diff --git a/src/Avalonia.Controls/ScrollViewer.cs b/src/Avalonia.Controls/ScrollViewer.cs
index af874bd380..0f1b8f388c 100644
--- a/src/Avalonia.Controls/ScrollViewer.cs
+++ b/src/Avalonia.Controls/ScrollViewer.cs
@@ -200,7 +200,7 @@ namespace Avalonia.Controls
                 ScrollBarVisibility.Auto);
 
         /// <summary>
-        /// Defines the <see cref="IsExpandedProperty"/> property.
+        /// Defines the <see cref="IsExpanded"/> property.
         /// </summary>
         public static readonly DirectProperty<ScrollViewer, bool> IsExpandedProperty =
             ScrollBar.IsExpandedProperty.AddOwner<ScrollViewer>(o => o.IsExpanded);
diff --git a/src/Avalonia.Controls/Slider.cs b/src/Avalonia.Controls/Slider.cs
index 7de726a932..a9c9f42af8 100644
--- a/src/Avalonia.Controls/Slider.cs
+++ b/src/Avalonia.Controls/Slider.cs
@@ -80,7 +80,7 @@ namespace Avalonia.Controls
             AvaloniaProperty.Register<Slider, TickPlacement>(nameof(TickPlacement), 0d);
 
         /// <summary>
-        /// Defines the <see cref="TicksProperty"/> property.
+        /// Defines the <see cref="Ticks"/> property.
         /// </summary>
         public static readonly StyledProperty<AvaloniaList<double>?> TicksProperty =
             TickBar.TicksProperty.AddOwner<Slider>();
diff --git a/src/Avalonia.Controls/TopLevel.cs b/src/Avalonia.Controls/TopLevel.cs
index dcf387afab..bf0de1d79f 100644
--- a/src/Avalonia.Controls/TopLevel.cs
+++ b/src/Avalonia.Controls/TopLevel.cs
@@ -75,7 +75,7 @@ namespace Avalonia.Controls
                 unsetValue: WindowTransparencyLevel.None);        
 
         /// <summary>
-        /// Defines the <see cref="TransparencyBackgroundFallbackProperty"/> property.
+        /// Defines the <see cref="TransparencyBackgroundFallback"/> property.
         /// </summary>
         public static readonly StyledProperty<IBrush> TransparencyBackgroundFallbackProperty =
             AvaloniaProperty.Register<TopLevel, IBrush>(nameof(TransparencyBackgroundFallback), Brushes.White);

From e3c1cbd2e09c2bf6f3ba091f441902b8aece2208 Mon Sep 17 00:00:00 2001
From: Julien Lebosquain <julien@lebosquain.net>
Date: Sun, 5 Mar 2023 12:42:46 +0100
Subject: [PATCH 16/40] Nullable annotations for Markup.Xaml

---
 src/Avalonia.Base/Styling/ITemplate.cs        |  2 +-
 .../Primitives/TemplatedControl.cs            | 19 ++++---
 .../Templates/IControlTemplate.cs             |  4 +-
 .../Avalonia.Markup.Xaml.csproj               |  2 +-
 .../AvaloniaXamlLoader.cs                     |  5 +-
 .../AvaloniaPropertyTypeConverter.cs          | 14 ++---
 .../Converters/AvaloniaUriTypeConverter.cs    |  6 ++-
 .../Converters/BitmapTypeConverter.cs         | 11 ++--
 .../Converters/ColorToBrushConverter.cs       |  8 +--
 .../Converters/FontFamilyTypeConverter.cs     | 10 ++--
 .../Converters/IconTypeConverter.cs           | 13 ++---
 .../Converters/PointsListTypeConverter.cs     |  9 ++--
 .../Converters/TimeSpanTypeConverter.cs       | 13 ++---
 src/Markup/Avalonia.Markup.Xaml/Extensions.cs | 31 ++++++-----
 .../CompiledBindingExtension.cs               | 12 +++--
 .../CompiledBindings/ArrayElementPlugin.cs    | 10 ++--
 .../CompiledBindings/CommandAccessorPlugin.cs | 36 ++++++-------
 .../CompiledBindings/CompiledBindingPath.cs   | 54 ++++++++++---------
 .../FindVisualAncestorNode.cs                 | 12 ++---
 .../CompiledBindings/MethodAccessorPlugin.cs  |  6 +--
 .../ObservableStreamPlugin.cs                 | 14 +++--
 .../PropertyInfoAccessorFactory.cs            | 52 +++++++++---------
 .../PropertyInfoAccessorPlugin.cs             | 11 ++--
 .../CompiledBindings/StrongTypeCastNode.cs    |  6 +--
 .../CompiledBindings/TaskStreamPlugin.cs      | 18 +++----
 .../DynamicResourceExtension.cs               |  4 +-
 .../MarkupExtensions/On.cs                    |  3 +-
 .../MarkupExtensions/OnFormFactorExtension.cs |  6 +--
 .../MarkupExtensions/OnPlatformExtension.cs   |  4 +-
 .../ReflectionBindingExtension.cs             | 27 +++++-----
 .../RelativeSourceExtension.cs                |  2 +-
 .../ResolveByNameExtension.cs                 | 11 ++--
 .../StaticResourceExtension.cs                | 34 ++++++------
 .../Parsers/PropertyParser.cs                 |  8 +--
 .../RuntimeXamlLoaderConfiguration.cs         |  2 -
 .../RuntimeXamlLoaderDocument.cs              |  3 +-
 .../Styling/MergeResourceInclude.cs           |  3 --
 .../Styling/ResourceInclude.cs                |  2 -
 .../Styling/StyleInclude.cs                   |  6 +--
 .../Templates/ControlTemplate.cs              |  6 +--
 .../Templates/DataTemplate.cs                 | 10 ++--
 .../Templates/ItemsPanelTemplate.cs           |  8 +--
 .../Templates/Template.cs                     |  8 +--
 .../Templates/TemplateContent.cs              | 17 +++---
 .../Templates/TreeDataTemplate.cs             | 12 ++---
 ...valoniaXamlIlXmlNamespaceInfoProviderV1.cs |  4 +-
 .../XamlIl/Runtime/XamlIlRuntimeHelpers.cs    | 40 +++++++-------
 src/Markup/Avalonia.Markup/Data/Binding.cs    |  3 +-
 .../Avalonia.Markup/Data/BindingBase.cs       |  5 +-
 .../Avalonia.Markup/Data/TemplateBinding.cs   | 27 ++++++----
 .../Markup/Data/DelayedBinding.cs             |  9 ++--
 .../Parsers/BindingExpressionGrammar.cs       |  6 +--
 .../Parsers/ExpressionObserverBuilder.cs      |  8 +--
 .../Markup/Parsers/ExpressionParser.cs        | 12 ++---
 .../Markup/Parsers/SelectorGrammar.cs         |  6 +--
 .../Xaml/ControlTemplateTests.cs              | 11 ++++
 56 files changed, 333 insertions(+), 352 deletions(-)

diff --git a/src/Avalonia.Base/Styling/ITemplate.cs b/src/Avalonia.Base/Styling/ITemplate.cs
index 8a130cb3b4..d183d3ff74 100644
--- a/src/Avalonia.Base/Styling/ITemplate.cs
+++ b/src/Avalonia.Base/Styling/ITemplate.cs
@@ -2,6 +2,6 @@
 {
     public interface ITemplate
     {
-        object Build();
+        object? Build();
     }
 }
diff --git a/src/Avalonia.Controls/Primitives/TemplatedControl.cs b/src/Avalonia.Controls/Primitives/TemplatedControl.cs
index e1cf25d89f..44d68fcf30 100644
--- a/src/Avalonia.Controls/Primitives/TemplatedControl.cs
+++ b/src/Avalonia.Controls/Primitives/TemplatedControl.cs
@@ -286,14 +286,17 @@ namespace Avalonia.Controls.Primitives
                 {
                     Logger.TryGet(LogEventLevel.Verbose, LogArea.Control)?.Log(this, "Creating control template");
 
-                    var (child, nameScope) = template.Build(this);
-                    ApplyTemplatedParent(child, this);
-                    ((ISetLogicalParent)child).SetParent(this);
-                    VisualChildren.Add(child);
-
-                    var e = new TemplateAppliedEventArgs(nameScope);
-                    OnApplyTemplate(e);
-                    RaiseEvent(e);
+                    if (template.Build(this) is { } templateResult)
+                    {
+                        var (child, nameScope) = templateResult;
+                        ApplyTemplatedParent(child, this);
+                        ((ISetLogicalParent)child).SetParent(this);
+                        VisualChildren.Add(child);
+
+                        var e = new TemplateAppliedEventArgs(nameScope);
+                        OnApplyTemplate(e);
+                        RaiseEvent(e);
+                    }
                 }
 
                 _appliedTemplate = template;
diff --git a/src/Avalonia.Controls/Templates/IControlTemplate.cs b/src/Avalonia.Controls/Templates/IControlTemplate.cs
index 67e861f6ab..38ad6561ab 100644
--- a/src/Avalonia.Controls/Templates/IControlTemplate.cs
+++ b/src/Avalonia.Controls/Templates/IControlTemplate.cs
@@ -1,13 +1,11 @@
-using System;
 using Avalonia.Controls.Primitives;
-using Avalonia.Styling;
 
 namespace Avalonia.Controls.Templates
 {
     /// <summary>
     /// Interface representing a template used to build a <see cref="TemplatedControl"/>.
     /// </summary>
-    public interface IControlTemplate : ITemplate<TemplatedControl, ControlTemplateResult>
+    public interface IControlTemplate : ITemplate<TemplatedControl, ControlTemplateResult?>
     {
     }
 
diff --git a/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj b/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj
index da739c754c..05e937fc05 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj
+++ b/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj
@@ -58,7 +58,6 @@
         <Compile Include="XamlIl\Runtime\IAvaloniaXamlIlXmlNamespaceInfoProviderV1.cs" />
         <Compile Include="XamlIl\Runtime\XamlIlRuntimeHelpers.cs" />
         <Compile Include="XamlLoadException.cs" />
-        <Compile Include="..\Avalonia.Markup\Markup\Parsers\BindingExpressionGrammar.cs" />
         <Compile Include="XamlTypes.cs" />
     </ItemGroup>
   <ItemGroup>
@@ -69,6 +68,7 @@
   <Import Project="..\..\..\build\ApiDiff.props" />
   <Import Project="..\..\..\build\DevAnalyzers.props" />
   <Import Project="..\..\..\build\TrimmingEnable.props" />
+  <Import Project="..\..\..\build\NullableEnable.props" />
 
   <ItemGroup Label="InternalsVisibleTo">
     <InternalsVisibleTo Include="Avalonia.Markup.Xaml.UnitTests, PublicKey=$(AvaloniaPublicKey)" />
diff --git a/src/Markup/Avalonia.Markup.Xaml/AvaloniaXamlLoader.cs b/src/Markup/Avalonia.Markup.Xaml/AvaloniaXamlLoader.cs
index 0b6a2c522f..834fa84b53 100644
--- a/src/Markup/Avalonia.Markup.Xaml/AvaloniaXamlLoader.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/AvaloniaXamlLoader.cs
@@ -1,8 +1,7 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
-using System.IO;
 using Avalonia.Platform;
-#nullable enable
+
 namespace Avalonia.Markup.Xaml
 {
     /// <summary>
@@ -79,7 +78,7 @@ namespace Avalonia.Markup.Xaml
 
             var compiledLoader = assetLocator.GetAssembly(uri, baseUri)
                 ?.GetType("CompiledAvaloniaXaml.!XamlLoader")
-                ?.GetMethod("TryLoad", new[] { typeof(System.IServiceProvider), typeof(string) });
+                ?.GetMethod("TryLoad", new[] { typeof(IServiceProvider), typeof(string) });
             if (compiledLoader != null)
             {
                 var compiledResult = compiledLoader.Invoke(null, new object?[] { sp, absoluteUri.ToString()});
diff --git a/src/Markup/Avalonia.Markup.Xaml/Converters/AvaloniaPropertyTypeConverter.cs b/src/Markup/Avalonia.Markup.Xaml/Converters/AvaloniaPropertyTypeConverter.cs
index 5b660af887..0a5ecebe5d 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Converters/AvaloniaPropertyTypeConverter.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Converters/AvaloniaPropertyTypeConverter.cs
@@ -14,18 +14,20 @@ namespace Avalonia.Markup.Xaml.Converters
     [RequiresUnreferencedCode(TrimmingMessages.XamlTypeResolvedRequiresUnreferenceCodeMessage)]
     public class AvaloniaPropertyTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var registry = AvaloniaPropertyRegistry.Instance;
             var (ns, owner, propertyName) = PropertyParser.Parse(new CharacterReader(((string)value).AsSpan()));
             var ownerType = TryResolveOwnerByName(context, ns, owner);
-            var targetType = context.GetFirstParent<ControlTemplate>()?.TargetType ??
-                context.GetFirstParent<Style>()?.Selector?.TargetType ??
+            var targetType = context?.GetFirstParent<ControlTemplate>()?.TargetType ??
+                context?.GetFirstParent<Style>()?.Selector?.TargetType ??
                 typeof(Control);
             var effectiveOwner = ownerType ?? targetType;
             var property = registry.FindRegistered(effectiveOwner, propertyName);
@@ -51,11 +53,11 @@ namespace Avalonia.Markup.Xaml.Converters
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.XamlTypeResolvedRequiresUnreferenceCodeMessage)]
-        private static Type TryResolveOwnerByName(ITypeDescriptorContext context, string ns, string owner)
+        private static Type? TryResolveOwnerByName(ITypeDescriptorContext? context, string? ns, string? owner)
         {
             if (owner != null)
             {
-                var result = context.ResolveType(ns, owner);
+                var result = context?.ResolveType(ns, owner);
 
                 if (result == null)
                 {
diff --git a/src/Markup/Avalonia.Markup.Xaml/Converters/AvaloniaUriTypeConverter.cs b/src/Markup/Avalonia.Markup.Xaml/Converters/AvaloniaUriTypeConverter.cs
index 54c57d8b7b..adfbef0231 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Converters/AvaloniaUriTypeConverter.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Converters/AvaloniaUriTypeConverter.cs
@@ -6,12 +6,14 @@ namespace Avalonia.Markup.Xaml.Converters
 {
     public class AvaloniaUriTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var s = value as string;
             if (s == null)
diff --git a/src/Markup/Avalonia.Markup.Xaml/Converters/BitmapTypeConverter.cs b/src/Markup/Avalonia.Markup.Xaml/Converters/BitmapTypeConverter.cs
index fc6a8557f3..6d455d0cc4 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Converters/BitmapTypeConverter.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Converters/BitmapTypeConverter.cs
@@ -1,20 +1,21 @@
 using System;
+using System.ComponentModel;
 using System.Globalization;
 using Avalonia.Media.Imaging;
 using Avalonia.Platform;
 
 namespace Avalonia.Markup.Xaml.Converters
 {
-    using System.ComponentModel;
-
     public class BitmapTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var s = (string)value;
             var uri = s.StartsWith("/")
@@ -25,7 +26,7 @@ namespace Avalonia.Markup.Xaml.Converters
                 return new Bitmap(uri.LocalPath);
 
             var assets = AvaloniaLocator.Current.GetRequiredService<IAssetLoader>();
-            return new Bitmap(assets.Open(uri, context.GetContextBaseUri()));
+            return new Bitmap(assets.Open(uri, context?.GetContextBaseUri()));
         }
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/Converters/ColorToBrushConverter.cs b/src/Markup/Avalonia.Markup.Xaml/Converters/ColorToBrushConverter.cs
index 5b44e9eb50..6fc378f088 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Converters/ColorToBrushConverter.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Converters/ColorToBrushConverter.cs
@@ -23,7 +23,7 @@ namespace Avalonia.Markup.Xaml.Converters
         /// If <paramref name="value"/> is a <see cref="Color"/> and <paramref name="targetType"/>
         /// is <see cref="IBrush"/> then converts the color to a solid color brush.
         /// </returns>
-        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
         {
             return Convert(value, targetType);
         }
@@ -40,7 +40,7 @@ namespace Avalonia.Markup.Xaml.Converters
         /// If <paramref name="value"/> is an <see cref="ISolidColorBrush"/> and <paramref name="targetType"/>
         /// is <see cref="Color"/> then converts the solid color brush to a color.
         /// </returns>
-        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
         {
             return ConvertBack(value, targetType);
         }
@@ -55,7 +55,7 @@ namespace Avalonia.Markup.Xaml.Converters
         /// If <paramref name="value"/> is a <see cref="Color"/> and <paramref name="targetType"/>
         /// is <see cref="IBrush"/> then converts the color to a solid color brush.
         /// </returns>
-        public static object Convert(object value, Type targetType)
+        public static object? Convert(object? value, Type? targetType)
         {
             if (targetType == typeof(IBrush) && value is Color c)
             {
@@ -75,7 +75,7 @@ namespace Avalonia.Markup.Xaml.Converters
         /// If <paramref name="value"/> is an <see cref="ISolidColorBrush"/> and <paramref name="targetType"/>
         /// is <see cref="Color"/> then converts the solid color brush to a color.
         /// </returns>
-        public static object ConvertBack(object value, Type targetType)
+        public static object? ConvertBack(object? value, Type? targetType)
         {
             if (targetType == typeof(Color) && value is ISolidColorBrush brush)
             {
diff --git a/src/Markup/Avalonia.Markup.Xaml/Converters/FontFamilyTypeConverter.cs b/src/Markup/Avalonia.Markup.Xaml/Converters/FontFamilyTypeConverter.cs
index b677cdfc22..55ce4e67eb 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Converters/FontFamilyTypeConverter.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Converters/FontFamilyTypeConverter.cs
@@ -1,24 +1,24 @@
 using System;
 using System.ComponentModel;
 using System.Globalization;
-
 using Avalonia.Media;
 
-
 namespace Avalonia.Markup.Xaml.Converters
 {
     public class FontFamilyTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var s = (string)value;
 
-            return FontFamily.Parse(s, context.GetContextBaseUri());
+            return FontFamily.Parse(s, context?.GetContextBaseUri());
         }
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/Converters/IconTypeConverter.cs b/src/Markup/Avalonia.Markup.Xaml/Converters/IconTypeConverter.cs
index 698f5a9327..c706fba2e7 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Converters/IconTypeConverter.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Converters/IconTypeConverter.cs
@@ -2,20 +2,21 @@
 using Avalonia.Media.Imaging;
 using Avalonia.Platform;
 using System;
+using System.ComponentModel;
 using System.Globalization;
 
 namespace Avalonia.Markup.Xaml.Converters
 {
-	using System.ComponentModel;
-
     public class IconTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var path = value as string;
             if (path != null)
@@ -32,7 +33,7 @@ namespace Avalonia.Markup.Xaml.Converters
             throw new NotSupportedException();
         }
 
-        private static WindowIcon CreateIconFromPath(ITypeDescriptorContext context, string s)
+        private static WindowIcon CreateIconFromPath(ITypeDescriptorContext? context, string s)
         {
             var uri = s.StartsWith("/")
                 ? new Uri(s, UriKind.Relative)
@@ -41,7 +42,7 @@ namespace Avalonia.Markup.Xaml.Converters
             if(uri.IsAbsoluteUri && uri.IsFile)
                 return new WindowIcon(uri.LocalPath);
             var assets = AvaloniaLocator.Current.GetRequiredService<IAssetLoader>();
-            return new WindowIcon(assets.Open(uri, context.GetContextBaseUri()));
+            return new WindowIcon(assets.Open(uri, context?.GetContextBaseUri()));
         }
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/Converters/PointsListTypeConverter.cs b/src/Markup/Avalonia.Markup.Xaml/Converters/PointsListTypeConverter.cs
index 099ffa8c8c..6a7d2a07d4 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Converters/PointsListTypeConverter.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Converters/PointsListTypeConverter.cs
@@ -1,20 +1,19 @@
 using System;
 using System.Collections.Generic;
+using System.ComponentModel;
 using System.Globalization;
+using Avalonia.Utilities;
 
 namespace Avalonia.Markup.Xaml.Converters
 {
-    using System.ComponentModel;
-    using Avalonia.Utilities;
-
     public class PointsListTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var points = new List<Point>();
 
diff --git a/src/Markup/Avalonia.Markup.Xaml/Converters/TimeSpanTypeConverter.cs b/src/Markup/Avalonia.Markup.Xaml/Converters/TimeSpanTypeConverter.cs
index 1b6fbcef5c..9da1fcf79b 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Converters/TimeSpanTypeConverter.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Converters/TimeSpanTypeConverter.cs
@@ -1,18 +1,13 @@
 using System;
+using System.ComponentModel;
 using System.Globalization;
 
 namespace Avalonia.Markup.Xaml.Converters
 {
-	using System.ComponentModel;
-
-    public class TimeSpanTypeConverter : System.ComponentModel.TimeSpanConverter
+    public class TimeSpanTypeConverter : TimeSpanConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
-        {
-            return base.CanConvertFrom(context, sourceType);
-        }
-
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var valueStr = (string)value;
             if (!valueStr.Contains(':'))
diff --git a/src/Markup/Avalonia.Markup.Xaml/Extensions.cs b/src/Markup/Avalonia.Markup.Xaml/Extensions.cs
index 903424253d..bbaf6e4074 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Extensions.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Extensions.cs
@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Avalonia.Controls;
@@ -11,38 +10,38 @@ namespace Avalonia.Markup.Xaml
 {
     internal static class Extensions
     {
-        public static T GetService<T>(this IServiceProvider sp) => (T)sp?.GetService(typeof(T));
-        
-        
-        public static Uri GetContextBaseUri(this IServiceProvider ctx) => ctx.GetService<IUriContext>().BaseUri;
+        public static T? GetService<T>(this IServiceProvider sp) => (T?)sp.GetService(typeof(T));
+
+        public static T GetRequiredService<T>(this IServiceProvider sp)
+            => sp.GetService<T>() ?? throw new InvalidOperationException($"Service {typeof(T)} hasn't been registered");
 
-        public static T GetFirstParent<T>(this IServiceProvider ctx) where T : class 
-            => ctx.GetService<IAvaloniaXamlIlParentStackProvider>().Parents.OfType<T>().FirstOrDefault();
+        public static Uri? GetContextBaseUri(this IServiceProvider ctx) => ctx.GetService<IUriContext>()?.BaseUri;
 
-        public static T GetLastParent<T>(this IServiceProvider ctx) where T : class 
-            => ctx.GetService<IAvaloniaXamlIlParentStackProvider>().Parents.OfType<T>().LastOrDefault();
+        public static T? GetFirstParent<T>(this IServiceProvider ctx) where T : class
+            => ctx.GetService<IAvaloniaXamlIlParentStackProvider>()?.Parents.OfType<T>().FirstOrDefault();
+
+        public static T? GetLastParent<T>(this IServiceProvider ctx) where T : class
+            => ctx.GetService<IAvaloniaXamlIlParentStackProvider>()?.Parents.OfType<T>().LastOrDefault();
 
         public static IEnumerable<T> GetParents<T>(this IServiceProvider sp)
-        {
-            return sp.GetService<IAvaloniaXamlIlParentStackProvider>().Parents.OfType<T>();
-        }
+            => sp.GetService<IAvaloniaXamlIlParentStackProvider>()?.Parents.OfType<T>() ?? Enumerable.Empty<T>();
 
         public static bool IsInControlTemplate(this IServiceProvider sp) => sp.GetService<IAvaloniaXamlIlControlTemplateProvider>() != null;
 
         [RequiresUnreferencedCode(TrimmingMessages.XamlTypeResolvedRequiresUnreferenceCodeMessage)]
-        public static Type ResolveType(this IServiceProvider ctx, string namespacePrefix, string type)
+        public static Type ResolveType(this IServiceProvider ctx, string? namespacePrefix, string type)
         {
             var tr = ctx.GetService<IXamlTypeResolver>();
             string name = string.IsNullOrEmpty(namespacePrefix) ? type : $"{namespacePrefix}:{type}";
-            return tr?.Resolve(name);
+            return tr?.Resolve(name) ?? throw new XamlLoadException($"Could not find type '{name}'.");
         }
         
-        public static object GetDefaultAnchor(this IServiceProvider provider)
+        public static object? GetDefaultAnchor(this IServiceProvider provider)
         {
             // If the target is not a control, so we need to find an anchor that will let us look
             // up named controls and style resources. First look for the closest Control in
             // the context.
-            object anchor = provider.GetFirstParent<Control>();
+            object? anchor = provider.GetFirstParent<Control>();
 
             if (anchor is null)
             {
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindingExtension.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindingExtension.cs
index d0a4de09ab..55aa262619 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindingExtension.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindingExtension.cs
@@ -35,7 +35,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
             };
         }
 
-        private protected override ExpressionObserver CreateExpressionObserver(AvaloniaObject target, AvaloniaProperty targetProperty, object anchor, bool enableDataValidation)
+        private protected override ExpressionObserver CreateExpressionObserver(AvaloniaObject target, AvaloniaProperty? targetProperty, object? anchor, bool enableDataValidation)
         {
             if (Source != null)
             {
@@ -61,8 +61,12 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
             }
             else
             {
+                var styledElement = target as StyledElement
+                    ?? anchor as StyledElement
+                    ?? throw new ArgumentException($"Cannot find a valid {nameof(StyledElement)} to use as the binding source.");
+
                 return CreateSourceObserver(
-                    (target as StyledElement) ?? (anchor as StyledElement),
+                    styledElement,
                     Path.BuildExpression(enableDataValidation));
             }
         }
@@ -70,8 +74,8 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
         [ConstructorArgument("path")]
         public CompiledBindingPath Path { get; set; }
 
-        public object Source { get; set; }
+        public object? Source { get; set; }
 
-        public Type DataType { get; set; }
+        public Type? DataType { get; set; }
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/ArrayElementPlugin.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/ArrayElementPlugin.cs
index 0302c8620d..ffd62dc858 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/ArrayElementPlugin.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/ArrayElementPlugin.cs
@@ -1,13 +1,11 @@
 using System;
-using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
-using System.Text;
 using Avalonia.Data;
 using Avalonia.Data.Core.Plugins;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
-    class ArrayElementPlugin : IPropertyAccessorPlugin
+    internal class ArrayElementPlugin : IPropertyAccessorPlugin
     {
         private readonly int[] _indices;
         private readonly Type _elementType;
@@ -25,7 +23,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.PropertyAccessorsRequiresUnreferencedCodeMessage)]
-        public IPropertyAccessor Start(WeakReference<object> reference, string propertyName)
+        public IPropertyAccessor? Start(WeakReference<object?> reference, string propertyName)
         {
             if (reference.TryGetTarget(out var target) && target is Array arr)
             {
@@ -48,9 +46,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
             public override Type PropertyType { get; }
 
-            public override object Value => _reference.TryGetTarget(out var arr) ? arr.GetValue(_indices) : null;
+            public override object? Value => _reference.TryGetTarget(out var arr) ? arr.GetValue(_indices) : null;
 
-            public override bool SetValue(object value, BindingPriority priority)
+            public override bool SetValue(object? value, BindingPriority priority)
             {
                 if (_reference.TryGetTarget(out var arr))
                 {
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CommandAccessorPlugin.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CommandAccessorPlugin.cs
index 4478a79d27..b9bc2a1e3c 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CommandAccessorPlugin.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CommandAccessorPlugin.cs
@@ -2,8 +2,6 @@
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
-using System.Reflection;
-using System.Text;
 using System.Windows.Input;
 using Avalonia.Data;
 using Avalonia.Data.Core.Plugins;
@@ -13,11 +11,11 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
     internal class CommandAccessorPlugin : IPropertyAccessorPlugin
     {
-        private readonly Action<object, object> _execute;
-        private readonly Func<object, object, bool> _canExecute;
+        private readonly Action<object, object?> _execute;
+        private readonly Func<object, object?, bool>? _canExecute;
         private readonly ISet<string> _dependsOnProperties;
 
-        public CommandAccessorPlugin(Action<object, object> execute, Func<object, object, bool> canExecute, ISet<string> dependsOnProperties)
+        public CommandAccessorPlugin(Action<object, object?> execute, Func<object, object?, bool>? canExecute, ISet<string> dependsOnProperties)
         {
             _execute = execute;
             _canExecute = canExecute;
@@ -31,18 +29,18 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.PropertyAccessorsRequiresUnreferencedCodeMessage)]
-        public IPropertyAccessor Start(WeakReference<object> reference, string propertyName)
+        public IPropertyAccessor Start(WeakReference<object?> reference, string propertyName)
         {
             return new CommandAccessor(reference, _execute, _canExecute, _dependsOnProperties);
         }
 
         private sealed class CommandAccessor : PropertyAccessorBase
         {
-            private readonly WeakReference<object> _reference;
-            private Command _command;
+            private readonly WeakReference<object?> _reference;
+            private readonly Command _command;
             private readonly ISet<string> _dependsOnProperties;
 
-            public CommandAccessor(WeakReference<object> reference, Action<object, object> execute, Func<object, object, bool> canExecute, ISet<string> dependsOnProperties)
+            public CommandAccessor(WeakReference<object?> reference, Action<object, object?> execute, Func<object, object?, bool>? canExecute, ISet<string> dependsOnProperties)
             {
                 _reference = reference ?? throw new ArgumentNullException(nameof(reference));
                 _dependsOnProperties = dependsOnProperties;
@@ -50,7 +48,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
             }
 
-            public override object Value => _reference.TryGetTarget(out var _) ? _command : null;
+            public override object? Value => _reference.TryGetTarget(out _) ? _command : null;
 
             private void RaiseCanExecuteChanged()
             {
@@ -59,13 +57,13 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
             private sealed class Command : ICommand
             {
-                private readonly WeakReference<object> _target;
-                private readonly Action<object, object> _execute;
-                private readonly Func<object, object, bool> _canExecute;
+                private readonly WeakReference<object?> _target;
+                private readonly Action<object, object?> _execute;
+                private readonly Func<object, object?, bool>? _canExecute;
 
-                public event EventHandler CanExecuteChanged;
+                public event EventHandler? CanExecuteChanged;
 
-                public Command(WeakReference<object> target, Action<object, object> execute, Func<object, object, bool> canExecute)
+                public Command(WeakReference<object?> target, Action<object, object?> execute, Func<object, object?, bool>? canExecute)
                 {
                     _target = target;
                     _execute = execute;
@@ -78,7 +76,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                        , Threading.DispatcherPriority.Input);
                 }
 
-                public bool CanExecute(object parameter)
+                public bool CanExecute(object? parameter)
                 {
                     if (_target.TryGetTarget(out var target))
                     {
@@ -91,7 +89,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                     return false;
                 }
 
-                public void Execute(object parameter)
+                public void Execute(object? parameter)
                 {
                     if (_target.TryGetTarget(out var target))
                     {
@@ -102,12 +100,12 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
             public override Type PropertyType => typeof(ICommand);
 
-            public override bool SetValue(object value, BindingPriority priority)
+            public override bool SetValue(object? value, BindingPriority priority)
             {
                 return false;
             }
 
-            void OnNotifyPropertyChanged(object sender, PropertyChangedEventArgs e)
+            private void OnNotifyPropertyChanged(object? sender, PropertyChangedEventArgs e)
             {
                 if (string.IsNullOrEmpty(e.PropertyName) || _dependsOnProperties.Contains(e.PropertyName))
                 {
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CompiledBindingPath.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CompiledBindingPath.cs
index f196231a6b..49349b047c 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CompiledBindingPath.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CompiledBindingPath.cs
@@ -17,7 +17,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         public CompiledBindingPath()
             => _elements = Array.Empty<ICompiledBindingPathElement>();
 
-        internal CompiledBindingPath(ICompiledBindingPathElement[] elements, object rawSource)
+        internal CompiledBindingPath(ICompiledBindingPathElement[] elements, object? rawSource)
         {
             _elements = elements;
             RawSource = rawSource;
@@ -26,14 +26,14 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = TrimmingMessages.CompiledBindingSafeSupressWarningMessage)]
         internal ExpressionNode BuildExpression(bool enableValidation)
         {
-            ExpressionNode pathRoot = null;
-            ExpressionNode path = null;
+            ExpressionNode? pathRoot = null;
+            ExpressionNode? path = null;
             foreach (var element in _elements)
             {
-                ExpressionNode node = null;
+                ExpressionNode? node;
                 switch (element)
                 {
-                    case NotExpressionPathElement _:
+                    case NotExpressionPathElement:
                         node = new LogicalNotNode();
                         break;
                     case PropertyElement prop:
@@ -54,7 +54,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                     case AncestorPathElement ancestor:
                         node = new FindAncestorNode(ancestor.AncestorType, ancestor.Level);
                         break;
-                    case SelfPathElement _:
+                    case SelfPathElement:
                         node = new SelfNode();
                         break;
                     case ElementNameElement name:
@@ -70,7 +70,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                         throw new InvalidOperationException($"Unknown binding path element type {element.GetType().FullName}");
                 }
 
-                path = pathRoot is null ? (pathRoot = node) : path.Next = node;
+                path = pathRoot is null ? (pathRoot = node) : path!.Next = node;
             }
 
             return pathRoot ?? new EmptyExpressionNode();
@@ -81,16 +81,17 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         internal SourceMode SourceMode => Array.Exists(_elements, e => e is IControlSourceBindingPathElement)
             ? SourceMode.Control : SourceMode.Data;
 
-        internal object RawSource { get; }
+        internal object? RawSource { get; }
 
+        /// <inheritdoc />
         public override string ToString()
             => string.Concat((IEnumerable<ICompiledBindingPathElement>) _elements);
     }
 
     public class CompiledBindingPathBuilder
     {
-        private object _rawSource;
-        private List<ICompiledBindingPathElement> _elements = new List<ICompiledBindingPathElement>();
+        private object? _rawSource;
+        private readonly List<ICompiledBindingPathElement> _elements = new();
 
         public CompiledBindingPathBuilder Not()
         {
@@ -98,7 +99,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             return this;
         }
 
-        public CompiledBindingPathBuilder Property(IPropertyInfo info, Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> accessorFactory)
+        public CompiledBindingPathBuilder Property(IPropertyInfo info, Func<WeakReference<object?>, IPropertyInfo, IPropertyAccessor> accessorFactory)
         {
             _elements.Add(new PropertyElement(info, accessorFactory, _elements.Count == 0));
             return this;
@@ -110,7 +111,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             return this;
         }
 
-        public CompiledBindingPathBuilder Command(string methodName, Action<object, object> executeHelper, Func<object, object, bool> canExecuteHelper, string[] dependsOnProperties)
+        public CompiledBindingPathBuilder Command(string methodName, Action<object, object?> executeHelper, Func<object, object?, bool>? canExecuteHelper, string[]? dependsOnProperties)
         {
             _elements.Add(new MethodAsCommandElement(methodName, executeHelper, canExecuteHelper, dependsOnProperties ?? Array.Empty<string>()));
             return this;
@@ -163,7 +164,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             return this;
         }
 
-        public CompiledBindingPathBuilder SetRawSource(object rawSource)
+        public CompiledBindingPathBuilder SetRawSource(object? rawSource)
         {
             _rawSource = rawSource;
             return this;
@@ -187,7 +188,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
     {
         private readonly bool _isFirstElement;
 
-        public PropertyElement(IPropertyInfo property, Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> accessorFactory, bool isFirstElement)
+        public PropertyElement(IPropertyInfo property, Func<WeakReference<object?>, IPropertyInfo, IPropertyAccessor> accessorFactory, bool isFirstElement)
         {
             Property = property;
             AccessorFactory = accessorFactory;
@@ -196,7 +197,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
         public IPropertyInfo Property { get; }
 
-        public Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> AccessorFactory { get; }
+        public Func<WeakReference<object?>, IPropertyInfo, IPropertyAccessor> AccessorFactory { get; }
 
         public override string ToString()
             => _isFirstElement ? Property.Name : $".{Property.Name}";
@@ -206,7 +207,8 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
     {
         public MethodAsDelegateElement(RuntimeMethodHandle method, RuntimeTypeHandle delegateType)
         {
-            Method = (MethodInfo)MethodBase.GetMethodFromHandle(method);
+            Method = MethodBase.GetMethodFromHandle(method) as MethodInfo
+                ?? throw new ArgumentException("Invalid method handle", nameof(method));
             DelegateType = Type.GetTypeFromHandle(delegateType);
         }
 
@@ -217,7 +219,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class MethodAsCommandElement : ICompiledBindingPathElement
     {
-        public MethodAsCommandElement(string methodName, Action<object, object> executeHelper, Func<object, object, bool> canExecuteHelper, string[] dependsOnElements)
+        public MethodAsCommandElement(string methodName, Action<object, object?> executeHelper, Func<object, object?, bool>? canExecuteHelper, string[] dependsOnElements)
         {
             MethodName = methodName;
             ExecuteMethod = executeHelper;
@@ -226,8 +228,8 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
 
         public string MethodName { get; }
-        public Action<object, object> ExecuteMethod { get; }
-        public Func<object, object, bool> CanExecuteMethod { get; }
+        public Action<object, object?> ExecuteMethod { get; }
+        public Func<object, object?, bool>? CanExecuteMethod { get; }
         public HashSet<string> DependsOnProperties { get; }
     }
 
@@ -240,7 +242,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
     {
         Type Type { get; }
 
-        Func<object, object> Cast { get; }
+        Func<object?, object?> Cast { get; }
     }
 
     internal class TaskStreamPathElement<T> : IStronglyTypedStreamElement
@@ -267,13 +269,13 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class AncestorPathElement : ICompiledBindingPathElement, IControlSourceBindingPathElement
     {
-        public AncestorPathElement(Type ancestorType, int level)
+        public AncestorPathElement(Type? ancestorType, int level)
         {
             AncestorType = ancestorType;
             Level = level;
         }
 
-        public Type AncestorType { get; }
+        public Type? AncestorType { get; }
         public int Level { get; }
 
         public override string ToString()
@@ -282,13 +284,13 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class VisualAncestorPathElement : ICompiledBindingPathElement, IControlSourceBindingPathElement
     {
-        public VisualAncestorPathElement(Type ancestorType, int level)
+        public VisualAncestorPathElement(Type? ancestorType, int level)
         {
             AncestorType = ancestorType;
             Level = level;
         }
 
-        public Type AncestorType { get; }
+        public Type? AncestorType { get; }
         public int Level { get; }
     }
 
@@ -323,7 +325,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class TypeCastPathElement<T> : ITypeCastElement
     {
-        private static object TryCast(object obj)
+        private static object? TryCast(object? obj)
         {
             if (obj is T result)
                 return result;
@@ -332,7 +334,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
         public Type Type => typeof(T);
 
-        public Func<object, object> Cast => TryCast;
+        public Func<object?, object?> Cast => TryCast;
 
         public override string ToString()
             => $"({Type.FullName})";
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/FindVisualAncestorNode.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/FindVisualAncestorNode.cs
index 170a31fd64..7c20f86074 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/FindVisualAncestorNode.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/FindVisualAncestorNode.cs
@@ -5,13 +5,13 @@ using Avalonia.Reactive;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
-    class FindVisualAncestorNode : ExpressionNode
+    internal class FindVisualAncestorNode : ExpressionNode
     {
         private readonly int _level;
-        private readonly Type _ancestorType;
-        private IDisposable _subscription;
+        private readonly Type? _ancestorType;
+        private IDisposable? _subscription;
 
-        public FindVisualAncestorNode(Type ancestorType, int level)
+        public FindVisualAncestorNode(Type? ancestorType, int level)
         {
             _level = level;
             _ancestorType = ancestorType;
@@ -32,9 +32,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             }
         }
 
-        protected override void StartListeningCore(WeakReference<object> reference)
+        protected override void StartListeningCore(WeakReference<object?> reference)
         {
-            if (reference.TryGetTarget(out object target) && target is Visual visual)
+            if (reference.TryGetTarget(out object? target) && target is Visual visual)
             {
                 _subscription = VisualLocator.Track(visual, _level, _ancestorType).Subscribe(ValueChanged);
             }
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/MethodAccessorPlugin.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/MethodAccessorPlugin.cs
index f3b7c664c9..e4d36a33a2 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/MethodAccessorPlugin.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/MethodAccessorPlugin.cs
@@ -1,19 +1,15 @@
 using System;
-using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
-using System.Text;
 using Avalonia.Data;
 using Avalonia.Data.Core.Plugins;
 
-#nullable enable
-
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
     internal class MethodAccessorPlugin : IPropertyAccessorPlugin
     {
-        private MethodInfo _method;
+        private readonly MethodInfo _method;
         private readonly Type _delegateType;
 
         public MethodAccessorPlugin(MethodInfo method, Type delegateType)
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/ObservableStreamPlugin.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/ObservableStreamPlugin.cs
index cb21df0507..93ff1ceacb 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/ObservableStreamPlugin.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/ObservableStreamPlugin.cs
@@ -1,33 +1,31 @@
 using System;
-using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
-using System.Text;
 using Avalonia.Data.Core.Plugins;
 using Avalonia.Reactive;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
-    class ObservableStreamPlugin<T> : IStreamPlugin
+    internal class ObservableStreamPlugin<T> : IStreamPlugin
     {
         [RequiresUnreferencedCode(TrimmingMessages.StreamPluginRequiresUnreferencedCodeMessage)]
-        public bool Match(WeakReference<object> reference)
+        public bool Match(WeakReference<object?> reference)
         {
             return reference.TryGetTarget(out var target) && target is IObservable<T>;
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.StreamPluginRequiresUnreferencedCodeMessage)]
-        public IObservable<object> Start(WeakReference<object> reference)
+        public IObservable<object?> Start(WeakReference<object?> reference)
         {
             if (!(reference.TryGetTarget(out var target) && target is IObservable<T> obs))
             {
-                return Observable.Empty<object>();
+                return Observable.Empty<object?>();
             }
-            else if (target is IObservable<object> obj)
+            else if (target is IObservable<object?> obj)
             {
                 return obj;
             }
 
-            return obs.Select(x => (object)x);
+            return obs.Select(x => (object?)x);
         }
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorFactory.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorFactory.cs
index 9e58f81b55..c8e65ff672 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorFactory.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorFactory.cs
@@ -11,29 +11,29 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
     public static class PropertyInfoAccessorFactory
     {
-        public static IPropertyAccessor CreateInpcPropertyAccessor(WeakReference<object> target, IPropertyInfo property)
+        public static IPropertyAccessor CreateInpcPropertyAccessor(WeakReference<object?> target, IPropertyInfo property)
             => new InpcPropertyAccessor(target, property);
 
-        public static IPropertyAccessor CreateAvaloniaPropertyAccessor(WeakReference<object> target, IPropertyInfo property)
-            => new AvaloniaPropertyAccessor(new WeakReference<AvaloniaObject>((AvaloniaObject)(target.TryGetTarget(out var o) ? o : null)), (AvaloniaProperty)property);
+        public static IPropertyAccessor CreateAvaloniaPropertyAccessor(WeakReference<object?> target, IPropertyInfo property)
+            => new AvaloniaPropertyAccessor(new WeakReference<AvaloniaObject?>((AvaloniaObject?)(target.TryGetTarget(out var o) ? o : null)), (AvaloniaProperty)property);
 
-        public static IPropertyAccessor CreateIndexerPropertyAccessor(WeakReference<object> target, IPropertyInfo property, int argument)
+        public static IPropertyAccessor CreateIndexerPropertyAccessor(WeakReference<object?> target, IPropertyInfo property, int argument)
             => new IndexerAccessor(target, property, argument);
     }
 
     internal class AvaloniaPropertyAccessor : PropertyAccessorBase
     {
-        private readonly WeakReference<AvaloniaObject> _reference;
+        private readonly WeakReference<AvaloniaObject?> _reference;
         private readonly AvaloniaProperty _property;
-        private IDisposable _subscription;
+        private IDisposable? _subscription;
 
-        public AvaloniaPropertyAccessor(WeakReference<AvaloniaObject> reference, AvaloniaProperty property)
+        public AvaloniaPropertyAccessor(WeakReference<AvaloniaObject?> reference, AvaloniaProperty property)
         {
-            _reference = reference ?? throw new ArgumentNullException(nameof(reference));;
-            _property = property ?? throw new ArgumentNullException(nameof(property));;
+            _reference = reference ?? throw new ArgumentNullException(nameof(reference));
+            _property = property ?? throw new ArgumentNullException(nameof(property));
         }
 
-        public AvaloniaObject Instance
+        public AvaloniaObject? Instance
         {
             get
             {
@@ -43,13 +43,13 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
 
         public override Type PropertyType => _property.PropertyType;
-        public override object Value => Instance?.GetValue(_property);
+        public override object? Value => Instance?.GetValue(_property);
 
-        public override bool SetValue(object value, BindingPriority priority)
+        public override bool SetValue(object? value, BindingPriority priority)
         {
-            if (!_property.IsReadOnly)
+            if (!_property.IsReadOnly && Instance is { } instance)
             {
-                Instance.SetValue(_property, value, priority);
+                instance.SetValue(_property, value, priority);
                 return true;
             }
 
@@ -70,10 +70,10 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class InpcPropertyAccessor : PropertyAccessorBase, IWeakEventSubscriber<PropertyChangedEventArgs>
     {
-        protected readonly WeakReference<object> _reference;
+        protected readonly WeakReference<object?> _reference;
         private readonly IPropertyInfo _property;
 
-        public InpcPropertyAccessor(WeakReference<object> reference, IPropertyInfo property)
+        public InpcPropertyAccessor(WeakReference<object?> reference, IPropertyInfo property)
         {
             _reference = reference ?? throw new ArgumentNullException(nameof(reference));
             _property = property ?? throw new ArgumentNullException(nameof(property));
@@ -81,7 +81,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
         public override Type PropertyType => _property.PropertyType;
 
-        public override object Value
+        public override object? Value
         {
             get
             {
@@ -89,7 +89,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             }
         }
 
-        public override bool SetValue(object value, BindingPriority priority)
+        public override bool SetValue(object? value, BindingPriority priority)
         {
             if (_property.CanSet && _reference.TryGetTarget(out var o))
             {
@@ -103,7 +103,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             return false;
         }
 
-        public void OnEvent(object sender, WeakEvent ev, PropertyChangedEventArgs e)
+        public void OnEvent(object? sender, WeakEvent ev, PropertyChangedEventArgs e)
         {
             if (e.PropertyName == _property.Name || string.IsNullOrEmpty(e.PropertyName))
             {
@@ -144,9 +144,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class IndexerAccessor : InpcPropertyAccessor, IWeakEventSubscriber<NotifyCollectionChangedEventArgs>
     {
-        private int _index;
+        private readonly int _index;
 
-        public IndexerAccessor(WeakReference<object> target, IPropertyInfo basePropertyInfo, int argument)
+        public IndexerAccessor(WeakReference<object?> target, IPropertyInfo basePropertyInfo, int argument)
             :base(target, basePropertyInfo)
         {
             _index = argument;
@@ -167,7 +167,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                 WeakEvents.CollectionChanged.Unsubscribe(incc, this);
         }
         
-        public void OnEvent(object sender, WeakEvent ev, NotifyCollectionChangedEventArgs args)
+        public void OnEvent(object? sender, WeakEvent ev, NotifyCollectionChangedEventArgs args)
         {
             if (ShouldNotifyListeners(args))
             {
@@ -175,7 +175,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             }
         }
 
-        bool ShouldNotifyListeners(NotifyCollectionChangedEventArgs e)
+        private bool ShouldNotifyListeners(NotifyCollectionChangedEventArgs e)
         {
             switch (e.Action)
             {
@@ -185,12 +185,12 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                     return _index >= e.OldStartingIndex;
                 case NotifyCollectionChangedAction.Replace:
                     return _index >= e.NewStartingIndex &&
-                           _index < e.NewStartingIndex + e.NewItems.Count;
+                           _index < e.NewStartingIndex + e.NewItems!.Count;
                 case NotifyCollectionChangedAction.Move:
                     return (_index >= e.NewStartingIndex &&
-                            _index < e.NewStartingIndex + e.NewItems.Count) ||
+                            _index < e.NewStartingIndex + e.NewItems!.Count) ||
                            (_index >= e.OldStartingIndex &&
-                            _index < e.OldStartingIndex + e.OldItems.Count);
+                            _index < e.OldStartingIndex + e.OldItems!.Count);
                 case NotifyCollectionChangedAction.Reset:
                     return true;
             }
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorPlugin.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorPlugin.cs
index 313b3ccef9..631f71faab 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorPlugin.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorPlugin.cs
@@ -1,20 +1,17 @@
 using System;
-using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
-using System.Text;
-using Avalonia.Data;
 using Avalonia.Data.Core;
 using Avalonia.Data.Core.Plugins;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
-    class PropertyInfoAccessorPlugin : IPropertyAccessorPlugin
+    internal class PropertyInfoAccessorPlugin : IPropertyAccessorPlugin
     {
         private readonly IPropertyInfo _propertyInfo;
-        private readonly Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> _accessorFactory;
+        private readonly Func<WeakReference<object?>, IPropertyInfo, IPropertyAccessor> _accessorFactory;
 
-        public PropertyInfoAccessorPlugin(IPropertyInfo propertyInfo, Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> accessorFactory)
+        public PropertyInfoAccessorPlugin(IPropertyInfo propertyInfo, Func<WeakReference<object?>, IPropertyInfo, IPropertyAccessor> accessorFactory)
         {
             _propertyInfo = propertyInfo;
             _accessorFactory = accessorFactory;
@@ -27,7 +24,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.PropertyAccessorsRequiresUnreferencedCodeMessage)]
-        public IPropertyAccessor Start(WeakReference<object> reference, string propertyName)
+        public IPropertyAccessor Start(WeakReference<object?> reference, string propertyName)
         {
             Debug.Assert(_propertyInfo.Name == propertyName);
             return _accessorFactory(reference, _propertyInfo);
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/StrongTypeCastNode.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/StrongTypeCastNode.cs
index b543fd9c01..360d34c881 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/StrongTypeCastNode.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/StrongTypeCastNode.cs
@@ -5,14 +5,14 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
     internal class StrongTypeCastNode : TypeCastNode
     {
-        private Func<object, object> _cast;
+        private readonly Func<object?, object?> _cast;
 
-        public StrongTypeCastNode(Type type, Func<object, object> cast) : base(type)
+        public StrongTypeCastNode(Type type, Func<object?, object?> cast) : base(type)
         {
             _cast = cast;
         }
 
-        protected override object Cast(object value)
+        protected override object? Cast(object? value)
             => _cast(value);
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/TaskStreamPlugin.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/TaskStreamPlugin.cs
index 7c9f7559c6..6f3e444ca2 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/TaskStreamPlugin.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/TaskStreamPlugin.cs
@@ -7,20 +7,20 @@ using Avalonia.Reactive;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
-    class TaskStreamPlugin<T> : IStreamPlugin
+    internal class TaskStreamPlugin<T> : IStreamPlugin
     {
         [RequiresUnreferencedCode(TrimmingMessages.StreamPluginRequiresUnreferencedCodeMessage)]
-        public bool Match(WeakReference<object> reference)
+        public bool Match(WeakReference<object?> reference)
         {
             return reference.TryGetTarget(out var target) && target is Task<T>;
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.StreamPluginRequiresUnreferencedCodeMessage)]
-        public IObservable<object> Start(WeakReference<object> reference)
+        public IObservable<object?> Start(WeakReference<object?> reference)
         {
             if(!(reference.TryGetTarget(out var target) && target is Task<T> task))
             {
-                return Observable.Empty<object>();
+                return Observable.Empty<object?>();
             }
 
             switch (task.Status)
@@ -29,9 +29,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                 case TaskStatus.Faulted:
                     return HandleCompleted(task);
                 default:
-                    var subject = new LightweightSubject<object>();
+                    var subject = new LightweightSubject<object?>();
                     task.ContinueWith(
-                            x => HandleCompleted(task).Subscribe(subject),
+                            _ => HandleCompleted(task).Subscribe(subject),
                             TaskScheduler.FromCurrentSynchronizationContext())
                         .ConfigureAwait(false);
                     return subject;
@@ -39,14 +39,14 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
         
         
-        private static IObservable<object> HandleCompleted(Task<T> task)
+        private static IObservable<object?> HandleCompleted(Task<T> task)
         {
             switch (task.Status)
             {
                 case TaskStatus.RanToCompletion:
-                    return Observable.Return((object)task.Result);
+                    return Observable.Return((object?)task.Result);
                 case TaskStatus.Faulted:
-                    return Observable.Return(new BindingNotification(task.Exception, BindingErrorType.Error));
+                    return Observable.Return(new BindingNotification(task.Exception!, BindingErrorType.Error));
                 default:
                     throw new AvaloniaInternalException("HandleCompleted called for non-completed Task.");
             }
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/DynamicResourceExtension.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/DynamicResourceExtension.cs
index 6084de7d7d..e1b594e331 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/DynamicResourceExtension.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/DynamicResourceExtension.cs
@@ -4,8 +4,6 @@ using Avalonia.Data;
 using Avalonia.Markup.Xaml.Converters;
 using Avalonia.Media;
 
-#nullable enable
-
 namespace Avalonia.Markup.Xaml.MarkupExtensions
 {
     public class DynamicResourceExtension : IBinding
@@ -31,7 +29,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
             var provideTarget = serviceProvider.GetService<IProvideValueTarget>();
 
-            if (!(provideTarget.TargetObject is StyledElement))
+            if (provideTarget?.TargetObject is not StyledElement)
             {
                 _anchor = serviceProvider.GetFirstParent<StyledElement>() ??
                     serviceProvider.GetFirstParent<IResourceProvider>() ??
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/On.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/On.cs
index 0752ab43b5..52313e735b 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/On.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/On.cs
@@ -1,5 +1,4 @@
-#nullable enable
-using System.Collections.Generic;
+using System.Collections.Generic;
 using Avalonia.Metadata;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions;
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/OnFormFactorExtension.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/OnFormFactorExtension.cs
index c2f1100eff..a07595a35b 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/OnFormFactorExtension.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/OnFormFactorExtension.cs
@@ -1,6 +1,4 @@
-#nullable enable
 using System;
-
 using Avalonia.Metadata;
 using Avalonia.Platform;
 
@@ -20,7 +18,7 @@ public sealed class OnFormFactorExtension : OnFormFactorExtensionBase<object, On
 
     public static bool ShouldProvideOption(IServiceProvider serviceProvider, FormFactorType option)
     {
-        return serviceProvider.GetService<IRuntimePlatform>().GetRuntimeInfo().FormFactor == option;
+        return serviceProvider.GetService<IRuntimePlatform>()?.GetRuntimeInfo().FormFactor == option;
     }
 }
 
@@ -38,7 +36,7 @@ public sealed class OnFormFactorExtension<TReturn> : OnFormFactorExtensionBase<T
 
     public static bool ShouldProvideOption(IServiceProvider serviceProvider, FormFactorType option)
     {
-        return serviceProvider.GetService<IRuntimePlatform>().GetRuntimeInfo().FormFactor == option;
+        return serviceProvider.GetService<IRuntimePlatform>()?.GetRuntimeInfo().FormFactor == option;
     }
 }
 
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/OnPlatformExtension.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/OnPlatformExtension.cs
index 1c20020978..e393fbc7cf 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/OnPlatformExtension.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/OnPlatformExtension.cs
@@ -1,6 +1,4 @@
-#nullable enable
-using System;
-using Avalonia.Compatibility;
+using Avalonia.Compatibility;
 using Avalonia.Metadata;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions;
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/ReflectionBindingExtension.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/ReflectionBindingExtension.cs
index ec667fdb5f..6e7a65f258 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/ReflectionBindingExtension.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/ReflectionBindingExtension.cs
@@ -2,7 +2,6 @@ using Avalonia.Data;
 using System;
 using Avalonia.Controls;
 using Avalonia.Data.Converters;
-using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions
@@ -21,11 +20,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
         public Binding ProvideValue(IServiceProvider serviceProvider)
         {
-            var descriptorContext = (ITypeDescriptorContext)serviceProvider;
-
             return new Binding
             {
-                TypeResolver = descriptorContext.ResolveType,
+                TypeResolver = serviceProvider.ResolveType,
                 Converter = Converter,
                 ConverterParameter = ConverterParameter,
                 ElementName = ElementName,
@@ -36,33 +33,33 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
                 Source = Source,
                 StringFormat = StringFormat,
                 RelativeSource = RelativeSource,
-                DefaultAnchor = new WeakReference(descriptorContext.GetDefaultAnchor()),
+                DefaultAnchor = new WeakReference(serviceProvider.GetDefaultAnchor()),
                 TargetNullValue = TargetNullValue,
-                NameScope = new WeakReference<INameScope>(serviceProvider.GetService<INameScope>())
+                NameScope = new WeakReference<INameScope?>(serviceProvider.GetService<INameScope>())
             };
         }
 
-        public IValueConverter Converter { get; set; }
+        public IValueConverter? Converter { get; set; }
 
-        public object ConverterParameter { get; set; }
+        public object? ConverterParameter { get; set; }
 
-        public string ElementName { get; set; }
+        public string? ElementName { get; set; }
 
-        public object FallbackValue { get; set; } = AvaloniaProperty.UnsetValue;
+        public object? FallbackValue { get; set; } = AvaloniaProperty.UnsetValue;
 
         public BindingMode Mode { get; set; }
 
         [ConstructorArgument("path")]
-        public string Path { get; set; }
+        public string Path { get; set; } = "";
 
         public BindingPriority Priority { get; set; } = BindingPriority.LocalValue;
 
-        public object Source { get; set; }
+        public object? Source { get; set; }
 
-        public string StringFormat { get; set; }
+        public string? StringFormat { get; set; }
 
-        public RelativeSource RelativeSource { get; set; }
+        public RelativeSource? RelativeSource { get; set; }
 
-        public object TargetNullValue { get; set; } = AvaloniaProperty.UnsetValue;
+        public object? TargetNullValue { get; set; } = AvaloniaProperty.UnsetValue;
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/RelativeSourceExtension.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/RelativeSourceExtension.cs
index f06644758f..fce026bb1c 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/RelativeSourceExtension.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/RelativeSourceExtension.cs
@@ -28,7 +28,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
         [ConstructorArgument("mode")]
         public RelativeSourceMode Mode { get; set; } = RelativeSourceMode.FindAncestor;
 
-        public Type AncestorType { get; set; }
+        public Type? AncestorType { get; set; }
 
         public TreeType Tree { get; set; }
 
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/ResolveByNameExtension.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/ResolveByNameExtension.cs
index 909462392c..db6e69f00f 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/ResolveByNameExtension.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/ResolveByNameExtension.cs
@@ -2,8 +2,6 @@
 using Avalonia.Controls;
 using Avalonia.Data.Core;
 
-#nullable  enable
-
 namespace Avalonia.Markup.Xaml.MarkupExtensions
 {
     public class ResolveByNameExtension
@@ -18,6 +16,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
         public object? ProvideValue(IServiceProvider serviceProvider)
         {
             var nameScope = serviceProvider.GetService<INameScope>();
+
+            if (nameScope is null)
+                return null;
             
             var value = nameScope.FindAsync(Name);
 
@@ -25,10 +26,12 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
                 return value.GetResult();
 
             var provideValueTarget = serviceProvider.GetService<IProvideValueTarget>();
-            var target = provideValueTarget.TargetObject;
 
-            if (provideValueTarget.TargetProperty is IPropertyInfo property) 
+            if (provideValueTarget?.TargetProperty is IPropertyInfo property)
+            {
+                var target = provideValueTarget.TargetObject;
                 value.OnCompleted(() => property.Set(target, value.GetResult()));
+            }
 
             return AvaloniaProperty.UnsetValue;
         }
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/StaticResourceExtension.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/StaticResourceExtension.cs
index bef32766dc..3de669b1e4 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/StaticResourceExtension.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/StaticResourceExtension.cs
@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using System.Reflection;
 using Avalonia.Controls;
 using Avalonia.Markup.Data;
@@ -8,8 +7,6 @@ using Avalonia.Markup.Xaml.Converters;
 using Avalonia.Markup.Xaml.XamlIl.Runtime;
 using Avalonia.Styling;
 
-#nullable enable
-
 namespace Avalonia.Markup.Xaml.MarkupExtensions
 {
     public class StaticResourceExtension
@@ -25,7 +22,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
         public object? ResourceKey { get; set; }
 
-        public object ProvideValue(IServiceProvider serviceProvider)
+        public object? ProvideValue(IServiceProvider serviceProvider)
         {
             if (ResourceKey is not { } resourceKey)
             {
@@ -34,32 +31,37 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
             var stack = serviceProvider.GetService<IAvaloniaXamlIlParentStackProvider>();
             var provideTarget = serviceProvider.GetService<IProvideValueTarget>();
-            var themeVariant = (provideTarget.TargetObject as IThemeVariantHost)?.ActualThemeVariant;
+            var targetObject = provideTarget?.TargetObject;
+            var targetProperty = provideTarget?.TargetProperty;
+            var themeVariant = (targetObject as IThemeVariantHost)?.ActualThemeVariant;
 
-            var targetType = provideTarget.TargetProperty switch
+            var targetType = targetProperty switch
             {
                 AvaloniaProperty ap => ap.PropertyType,
                 PropertyInfo pi => pi.PropertyType,
-                _ => null,
+                _ => null
             };
 
-            if (provideTarget.TargetObject is Setter { Property: not null } setter)
+            if (targetObject is Setter { Property: { } setterProperty })
             {
-                targetType = setter.Property?.PropertyType;
+                targetType = setterProperty.PropertyType;
             }
-            
+
             // Look upwards though the ambient context for IResourceNodes
             // which might be able to give us the resource.
-            foreach (var parent in stack.Parents)
+            if (stack is not null)
             {
-                if (parent is IResourceNode node && node.TryGetResource(resourceKey, themeVariant, out var value))
+                foreach (var parent in stack.Parents)
                 {
-                    return ColorToBrushConverter.Convert(value, targetType);
+                    if (parent is IResourceNode node && node.TryGetResource(resourceKey, themeVariant, out var value))
+                    {
+                        return ColorToBrushConverter.Convert(value, targetType);
+                    }
                 }
             }
 
-            if (provideTarget.TargetObject is Control target &&
-                provideTarget.TargetProperty is PropertyInfo property)
+            if (targetObject is Control target &&
+                targetProperty is PropertyInfo property)
             {
                 // This is stored locally to avoid allocating closure in the outer scope.
                 var localTargetType = targetType;
@@ -72,7 +74,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
             throw new KeyNotFoundException($"Static resource '{resourceKey}' not found.");
         }
 
-        private object GetValue(StyledElement control, Type? targetType)
+        private object? GetValue(StyledElement control, Type? targetType)
         {
             return ColorToBrushConverter.Convert(control.FindResource(ResourceKey!), targetType);
         }
diff --git a/src/Markup/Avalonia.Markup.Xaml/Parsers/PropertyParser.cs b/src/Markup/Avalonia.Markup.Xaml/Parsers/PropertyParser.cs
index 507e0690fd..a55a44dfe5 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Parsers/PropertyParser.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Parsers/PropertyParser.cs
@@ -5,7 +5,7 @@ namespace Avalonia.Markup.Xaml.Parsers
 {
     internal class PropertyParser
     {
-        public static (string ns, string owner, string name) Parse(CharacterReader r)
+        public static (string? ns, string? owner, string name) Parse(CharacterReader r)
         {
             if (r.End)
             {
@@ -14,9 +14,9 @@ namespace Avalonia.Markup.Xaml.Parsers
 
             var openParens = r.TakeIf('(');
             bool closeParens = false;
-            string ns = null;
-            string owner = null;
-            string name = null;
+            string? ns = null;
+            string? owner = null;
+            string? name = null;
 
             do
             {
diff --git a/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderConfiguration.cs b/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderConfiguration.cs
index b06f9a927e..1cd48f87d7 100644
--- a/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderConfiguration.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderConfiguration.cs
@@ -2,8 +2,6 @@ using System.Reflection;
 
 namespace Avalonia.Markup.Xaml;
 
-#nullable enable
-
 public class RuntimeXamlLoaderConfiguration
 {
     /// <summary>
diff --git a/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderDocument.cs b/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderDocument.cs
index 80335bbf53..4f6b1c4eef 100644
--- a/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderDocument.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderDocument.cs
@@ -1,5 +1,4 @@
-#nullable enable
-using System;
+using System;
 using System.IO;
 using System.Text;
 
diff --git a/src/Markup/Avalonia.Markup.Xaml/Styling/MergeResourceInclude.cs b/src/Markup/Avalonia.Markup.Xaml/Styling/MergeResourceInclude.cs
index d231a1d221..59a2ac02bf 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Styling/MergeResourceInclude.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Styling/MergeResourceInclude.cs
@@ -1,8 +1,5 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
-using Avalonia.Controls;
-
-#nullable enable
 
 namespace Avalonia.Markup.Xaml.Styling;
 
diff --git a/src/Markup/Avalonia.Markup.Xaml/Styling/ResourceInclude.cs b/src/Markup/Avalonia.Markup.Xaml/Styling/ResourceInclude.cs
index 4ff105cf1f..fbcfdde565 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Styling/ResourceInclude.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Styling/ResourceInclude.cs
@@ -3,8 +3,6 @@ using System.Diagnostics.CodeAnalysis;
 using Avalonia.Controls;
 using Avalonia.Styling;
 
-#nullable enable
-
 namespace Avalonia.Markup.Xaml.Styling
 {
     /// <summary>
diff --git a/src/Markup/Avalonia.Markup.Xaml/Styling/StyleInclude.cs b/src/Markup/Avalonia.Markup.Xaml/Styling/StyleInclude.cs
index 27367fce5e..420135a1b1 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Styling/StyleInclude.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Styling/StyleInclude.cs
@@ -4,8 +4,6 @@ using Avalonia.Controls;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 
-#nullable enable
-
 namespace Avalonia.Markup.Xaml.Styling
 {
     /// <summary>
@@ -65,11 +63,11 @@ namespace Avalonia.Markup.Xaml.Styling
                     _isLoading = false;
                 }
 
-                return _loaded?[0]!;
+                return _loaded[0];
             }
         }
 
-        bool IResourceNode.HasResources => Loaded?.HasResources ?? false;
+        bool IResourceNode.HasResources => Loaded.HasResources;
 
         IReadOnlyList<IStyle> IStyle.Children => _loaded ?? Array.Empty<IStyle>();
 
diff --git a/src/Markup/Avalonia.Markup.Xaml/Templates/ControlTemplate.cs b/src/Markup/Avalonia.Markup.Xaml/Templates/ControlTemplate.cs
index 6057e7ad05..4bbdda31d8 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Templates/ControlTemplate.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Templates/ControlTemplate.cs
@@ -9,10 +9,10 @@ namespace Avalonia.Markup.Xaml.Templates
     {
         [Content]
         [TemplateContent]
-        public object Content { get; set; }
+        public object? Content { get; set; }
 
-        public Type TargetType { get; set; }
+        public Type? TargetType { get; set; }
 
-        public ControlTemplateResult Build(TemplatedControl control) => TemplateContent.Load(Content);
+        public ControlTemplateResult? Build(TemplatedControl control) => TemplateContent.Load(Content);
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/Templates/DataTemplate.cs b/src/Markup/Avalonia.Markup.Xaml/Templates/DataTemplate.cs
index d9009b84b1..89b0468c6e 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Templates/DataTemplate.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Templates/DataTemplate.cs
@@ -8,13 +8,13 @@ namespace Avalonia.Markup.Xaml.Templates
     public class DataTemplate : IRecyclingDataTemplate, ITypedDataTemplate
     {
         [DataType]
-        public Type DataType { get; set; }
+        public Type? DataType { get; set; }
 
         [Content]
         [TemplateContent]
-        public object Content { get; set; }
+        public object? Content { get; set; }
 
-        public bool Match(object data)
+        public bool Match(object? data)
         {
             if (DataType == null)
             {
@@ -26,9 +26,9 @@ namespace Avalonia.Markup.Xaml.Templates
             }
         }
 
-        public Control Build(object data) => Build(data, null);
+        public Control? Build(object? data) => Build(data, null);
 
-        public Control Build(object data, Control existing)
+        public Control? Build(object? data, Control? existing)
         {
             return existing ?? TemplateContent.Load(Content)?.Control;
         }
diff --git a/src/Markup/Avalonia.Markup.Xaml/Templates/ItemsPanelTemplate.cs b/src/Markup/Avalonia.Markup.Xaml/Templates/ItemsPanelTemplate.cs
index 9e5da74135..c228a58990 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Templates/ItemsPanelTemplate.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Templates/ItemsPanelTemplate.cs
@@ -4,14 +4,14 @@ using Avalonia.Styling;
 
 namespace Avalonia.Markup.Xaml.Templates
 {
-    public class ItemsPanelTemplate : ITemplate<Panel>
+    public class ItemsPanelTemplate : ITemplate<Panel?>
     {
         [Content]
         [TemplateContent]
-        public object Content { get; set; }
+        public object? Content { get; set; }
 
-        public Panel Build() => (Panel)TemplateContent.Load(Content)?.Control;
+        public Panel? Build() => (Panel?)TemplateContent.Load(Content)?.Control;
 
-        object ITemplate.Build() => Build();
+        object? ITemplate.Build() => Build();
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/Templates/Template.cs b/src/Markup/Avalonia.Markup.Xaml/Templates/Template.cs
index 6dfa2755a6..62febebc8c 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Templates/Template.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Templates/Template.cs
@@ -4,14 +4,14 @@ using Avalonia.Styling;
 
 namespace Avalonia.Markup.Xaml.Templates
 {
-    public class Template : ITemplate<Control>
+    public class Template : ITemplate<Control?>
     {
         [Content]
         [TemplateContent]
-        public object Content { get; set; }
+        public object? Content { get; set; }
 
-        public Control Build() => TemplateContent.Load(Content)?.Control;
+        public Control? Build() => TemplateContent.Load(Content)?.Control;
 
-        object ITemplate.Build() => Build();
+        object? ITemplate.Build() => Build();
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/Templates/TemplateContent.cs b/src/Markup/Avalonia.Markup.Xaml/Templates/TemplateContent.cs
index 23166170db..08e897c514 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Templates/TemplateContent.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Templates/TemplateContent.cs
@@ -3,14 +3,13 @@ using Avalonia.Controls.Templates;
 
 namespace Avalonia.Markup.Xaml.Templates
 {
-    
     public static class TemplateContent
     {
-        public static ControlTemplateResult Load(object templateContent)
+        public static ControlTemplateResult? Load(object? templateContent)
         {
-            if (templateContent is Func<IServiceProvider, object> direct)
+            if (templateContent is Func<IServiceProvider?, object?> direct)
             {
-                return (ControlTemplateResult)direct(null);
+                return (ControlTemplateResult?)direct(null);
             }
 
             if (templateContent is null)
@@ -18,18 +17,18 @@ namespace Avalonia.Markup.Xaml.Templates
                 return null;
             }
 
-            throw new ArgumentException(nameof(templateContent));
+            throw new ArgumentException($"Unexpected content {templateContent.GetType()}", nameof(templateContent));
         }
 
-        public static TemplateResult<T> Load<T>(object templateContent)
+        public static TemplateResult<T>? Load<T>(object? templateContent)
         {
-            if (templateContent is Func<IServiceProvider, object> direct)
-                return (TemplateResult<T>)direct(null);
+            if (templateContent is Func<IServiceProvider?, object?> direct)
+                return (TemplateResult<T>?)direct(null);
 
             if (templateContent is null)
                 return null;
 
-            throw new ArgumentException(nameof(templateContent));
+            throw new ArgumentException($"Unexpected content {templateContent.GetType()}", nameof(templateContent));
         }
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/Templates/TreeDataTemplate.cs b/src/Markup/Avalonia.Markup.Xaml/Templates/TreeDataTemplate.cs
index 6502267703..a5b308523f 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Templates/TreeDataTemplate.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Templates/TreeDataTemplate.cs
@@ -13,16 +13,16 @@ namespace Avalonia.Markup.Xaml.Templates
     public class TreeDataTemplate : ITreeDataTemplate, ITypedDataTemplate
     {
         [DataType]
-        public Type DataType { get; set; }
+        public Type? DataType { get; set; }
 
         [Content]
         [TemplateContent]
-        public object Content { get; set; }
+        public object? Content { get; set; }
 
         [AssignBinding]
-        public BindingBase ItemsSource { get; set; }
+        public BindingBase? ItemsSource { get; set; }
 
-        public bool Match(object data)
+        public bool Match(object? data)
         {
             if (DataType == null)
             {
@@ -35,7 +35,7 @@ namespace Avalonia.Markup.Xaml.Templates
         }
 
         [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "If ItemsSource is a CompiledBinding, then path members will be preserver")]
-        public InstancedBinding ItemsSelector(object item)
+        public InstancedBinding? ItemsSelector(object item)
         {
             if (ItemsSource != null)
             {
@@ -52,7 +52,7 @@ namespace Avalonia.Markup.Xaml.Templates
             return null;
         }
 
-        public Control Build(object data)
+        public Control? Build(object? data)
         {
             var visualTreeForItem = TemplateContent.Load(Content)?.Control;
             if (visualTreeForItem != null)
diff --git a/src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/IAvaloniaXamlIlXmlNamespaceInfoProviderV1.cs b/src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/IAvaloniaXamlIlXmlNamespaceInfoProviderV1.cs
index afe7552e1b..77d797762c 100644
--- a/src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/IAvaloniaXamlIlXmlNamespaceInfoProviderV1.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/IAvaloniaXamlIlXmlNamespaceInfoProviderV1.cs
@@ -9,7 +9,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
     
     public class AvaloniaXamlIlXmlNamespaceInfo
     {
-        public string ClrNamespace { get; set; }
-        public string ClrAssemblyName { get; set; }
+        public string ClrNamespace { get; set; } = string.Empty;
+        public string ClrAssemblyName { get; set; } = string.Empty;
     }
 }
diff --git a/src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/XamlIlRuntimeHelpers.cs b/src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/XamlIlRuntimeHelpers.cs
index 6ef09bbb85..ba96ac15b3 100644
--- a/src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/XamlIlRuntimeHelpers.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/XamlIlRuntimeHelpers.cs
@@ -6,10 +6,7 @@ using System.Reflection;
 using Avalonia.Controls;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
-using Avalonia.Markup.Xaml.MarkupExtensions;
-using Avalonia.Markup.Xaml.Styling;
 using Avalonia.Platform;
-using Avalonia.Styling;
 
 // ReSharper disable UnusedMember.Global
 // ReSharper disable UnusedParameter.Global
@@ -27,9 +24,9 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
         public static Func<IServiceProvider, object> DeferredTransformationFactoryV2<T>(Func<IServiceProvider, object> builder,
             IServiceProvider provider)
         {
-            var resourceNodes = provider.GetService<IAvaloniaXamlIlParentStackProvider>().Parents
+            var resourceNodes = provider.GetRequiredService<IAvaloniaXamlIlParentStackProvider>().Parents
                 .OfType<IResourceNode>().ToList();
-            var rootObject = provider.GetService<IRootObjectProvider>().RootObject;
+            var rootObject = provider.GetRequiredService<IRootObjectProvider>().RootObject;
             var parentScope = provider.GetService<INameScope>();
             return sp =>
             {
@@ -44,17 +41,17 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
             };
         }
 
-        class DeferredParentServiceProvider :
+        private class DeferredParentServiceProvider :
             IAvaloniaXamlIlParentStackProvider,
             IServiceProvider,
             IRootObjectProvider,
             IAvaloniaXamlIlControlTemplateProvider
         {
-            private readonly IServiceProvider _parentProvider;
-            private readonly List<IResourceNode> _parentResourceNodes;
+            private readonly IServiceProvider? _parentProvider;
+            private readonly List<IResourceNode>? _parentResourceNodes;
             private readonly INameScope _nameScope;
 
-            public DeferredParentServiceProvider(IServiceProvider parentProvider, List<IResourceNode> parentResourceNodes,
+            public DeferredParentServiceProvider(IServiceProvider? parentProvider, List<IResourceNode>? parentResourceNodes,
                 object rootObject, INameScope nameScope)
             {
                 _parentProvider = parentProvider;
@@ -73,7 +70,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
                     yield return p;
             }
 
-            public object GetService(Type serviceType)
+            public object? GetService(Type serviceType)
             {
                 if (serviceType == typeof(INameScope))
                     return _nameScope;
@@ -115,25 +112,25 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
         public static IServiceProvider CreateInnerServiceProviderV1(IServiceProvider compiled)
             => new InnerServiceProvider(compiled);
 
-        class InnerServiceProvider : IServiceProvider
+        private class InnerServiceProvider : IServiceProvider
         {
             private readonly IServiceProvider _compiledProvider;
-            private XamlTypeResolver _resolver;
+            private XamlTypeResolver? _resolver;
 
             public InnerServiceProvider(IServiceProvider compiledProvider)
             {
                 _compiledProvider = compiledProvider;
             }
-            public object GetService(Type serviceType)
+            public object? GetService(Type serviceType)
             {
                 if (serviceType == typeof(IXamlTypeResolver))
-                    return _resolver ?? (_resolver = new XamlTypeResolver(
-                               _compiledProvider.GetService<IAvaloniaXamlIlXmlNamespaceInfoProvider>()));
+                    return _resolver ??= new XamlTypeResolver(
+                        _compiledProvider.GetRequiredService<IAvaloniaXamlIlXmlNamespaceInfoProvider>());
                 return null;
             }
         }
 
-        class XamlTypeResolver : IXamlTypeResolver
+        private class XamlTypeResolver : IXamlTypeResolver
         {
             private readonly IAvaloniaXamlIlXmlNamespaceInfoProvider _nsInfo;
 
@@ -148,7 +145,6 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
                 var sp = qualifiedTypeName.Split(new[] {':'}, 2);
                 var (ns, name) = sp.Length == 1 ? ("", qualifiedTypeName) : (sp[0], sp[1]);
                 var namespaces = _nsInfo.XmlNamespaces;
-                var dic = (Dictionary<string, IReadOnlyList<AvaloniaXamlIlXmlNamespaceInfo>>)namespaces;
                 if (!namespaces.TryGetValue(ns, out var lst))
                     throw new ArgumentException("Unable to resolve namespace for type " + qualifiedTypeName);
                 foreach (var entry in lst)
@@ -177,20 +173,20 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
         }
         #line default
 
-        class RootServiceProvider : IServiceProvider
+        private class RootServiceProvider : IServiceProvider
         {
             private readonly INameScope _nameScope;
-            private readonly IServiceProvider _parentServiceProvider;
-            private readonly IRuntimePlatform _runtimePlatform;
+            private readonly IServiceProvider? _parentServiceProvider;
+            private readonly IRuntimePlatform? _runtimePlatform;
 
-            public RootServiceProvider(INameScope nameScope, IServiceProvider parentServiceProvider)
+            public RootServiceProvider(INameScope nameScope, IServiceProvider? parentServiceProvider)
             {
                 _nameScope = nameScope;
                 _parentServiceProvider = parentServiceProvider;
                 _runtimePlatform = AvaloniaLocator.Current.GetService<IRuntimePlatform>();
             }
 
-            public object GetService(Type serviceType)
+            public object? GetService(Type serviceType)
             {
                 if (serviceType == typeof(INameScope))
                     return _nameScope;
diff --git a/src/Markup/Avalonia.Markup/Data/Binding.cs b/src/Markup/Avalonia.Markup/Data/Binding.cs
index 37e7be5e3f..82e68e1ec5 100644
--- a/src/Markup/Avalonia.Markup/Data/Binding.cs
+++ b/src/Markup/Avalonia.Markup/Data/Binding.cs
@@ -16,7 +16,6 @@ namespace Avalonia.Data
         /// Initializes a new instance of the <see cref="Binding"/> class.
         /// </summary>
         public Binding()
-            :base()
         {
         }
 
@@ -54,7 +53,7 @@ namespace Avalonia.Data
         /// <summary>
         /// Gets or sets a function used to resolve types from names in the binding path.
         /// </summary>
-        public Func<string, string, Type>? TypeResolver { get; set; }
+        public Func<string?, string, Type>? TypeResolver { get; set; }
 
         private protected override ExpressionObserver CreateExpressionObserver(AvaloniaObject target, AvaloniaProperty? targetProperty, object? anchor, bool enableDataValidation)
         {
diff --git a/src/Markup/Avalonia.Markup/Data/BindingBase.cs b/src/Markup/Avalonia.Markup/Data/BindingBase.cs
index 8c8c50763b..17f44a4b54 100644
--- a/src/Markup/Avalonia.Markup/Data/BindingBase.cs
+++ b/src/Markup/Avalonia.Markup/Data/BindingBase.cs
@@ -7,7 +7,6 @@ using Avalonia.LogicalTree;
 using Avalonia.Reactive;
 using Avalonia.VisualTree;
 
-
 namespace Avalonia.Data
 {
     public abstract class BindingBase : IBinding
@@ -68,7 +67,7 @@ namespace Avalonia.Data
 
         public WeakReference? DefaultAnchor { get; set; }
 
-        public WeakReference<INameScope>? NameScope { get; set; }
+        public WeakReference<INameScope?>? NameScope { get; set; }
 
         private protected abstract ExpressionObserver CreateExpressionObserver(
             AvaloniaObject target,
@@ -169,7 +168,7 @@ namespace Avalonia.Data
         {
             _ = target ?? throw new ArgumentNullException(nameof(target));
 
-            if (NameScope is null || !NameScope.TryGetTarget(out var scope) || scope is null)
+            if (NameScope is null || !NameScope.TryGetTarget(out var scope))
                 throw new InvalidOperationException("Name scope is null or was already collected");
             var result = new ExpressionObserver(
                 NameScopeLocator.Track(scope, elementName),
diff --git a/src/Markup/Avalonia.Markup/Data/TemplateBinding.cs b/src/Markup/Avalonia.Markup/Data/TemplateBinding.cs
index cfb1b508d9..70e5fce853 100644
--- a/src/Markup/Avalonia.Markup/Data/TemplateBinding.cs
+++ b/src/Markup/Avalonia.Markup/Data/TemplateBinding.cs
@@ -16,7 +16,7 @@ namespace Avalonia.Data
         ISetterValue
     {
         private bool _isSetterValue;
-        private StyledElement _target = default!;
+        private StyledElement? _target;
         private Type? _targetType;
         private bool _hasProducedValue;
 
@@ -42,7 +42,7 @@ namespace Avalonia.Data
             //
             // If the binding appears in a `Setter`, then make a clone and instantiate that because
             // because the setter can outlive the control and cause a leak.
-            if (_target == null && !_isSetterValue)
+            if (_target is null && !_isSetterValue)
             {
                 _target = (StyledElement)target;
                 _targetType = targetProperty?.PropertyType;
@@ -93,9 +93,9 @@ namespace Avalonia.Data
 
         void IObserver<object?>.OnNext(object? value)
         {
-            if (_target.TemplatedParent is AvaloniaObject templatedParent && Property != null)
+            if (_target?.TemplatedParent is { } templatedParent && Property is not null)
             {
-                if (Converter != null)
+                if (Converter is not null)
                 {
                     value = Converter.ConvertBack(
                         value,
@@ -114,24 +114,31 @@ namespace Avalonia.Data
         protected override void Subscribed()
         {
             TemplatedParentChanged();
-            _target.PropertyChanged += TargetPropertyChanged;
+
+            if (_target is not null)
+            {
+                _target.PropertyChanged += TargetPropertyChanged;
+            }
         }
 
         protected override void Unsubscribed()
         {
-            if (_target.TemplatedParent is AvaloniaObject templatedParent)
+            if (_target?.TemplatedParent is { } templatedParent)
             {
                 templatedParent.PropertyChanged -= TemplatedParentPropertyChanged;
             }
 
-            _target.PropertyChanged -= TargetPropertyChanged;
+            if (_target is not null)
+            {
+                _target.PropertyChanged -= TargetPropertyChanged;
+            }
         }
 
         private void PublishValue()
         {
-            if (_target.TemplatedParent is AvaloniaObject templatedParent)
+            if (_target?.TemplatedParent is { } templatedParent)
             {
-                var value = Property != null ?
+                var value = Property is not null ?
                     templatedParent.GetValue(Property) :
                     _target.TemplatedParent;
 
@@ -152,7 +159,7 @@ namespace Avalonia.Data
 
         private void TemplatedParentChanged()
         {
-            if (_target.TemplatedParent is AvaloniaObject templatedParent)
+            if (_target?.TemplatedParent is { } templatedParent)
             {
                 templatedParent.PropertyChanged += TemplatedParentPropertyChanged;
             }
diff --git a/src/Markup/Avalonia.Markup/Markup/Data/DelayedBinding.cs b/src/Markup/Avalonia.Markup/Markup/Data/DelayedBinding.cs
index 98a3f023b6..551e017a61 100644
--- a/src/Markup/Avalonia.Markup/Markup/Data/DelayedBinding.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Data/DelayedBinding.cs
@@ -20,8 +20,7 @@ namespace Avalonia.Markup.Data
     /// </remarks>
     public static class DelayedBinding
     {
-        private static ConditionalWeakTable<StyledElement, List<Entry>> _entries = 
-            new ConditionalWeakTable<StyledElement, List<Entry>>();
+        private static readonly ConditionalWeakTable<StyledElement, List<Entry>> _entries = new();
 
         /// <summary>
         /// Adds a delayed binding to a control.
@@ -57,7 +56,7 @@ namespace Avalonia.Markup.Data
         /// <param name="target">The control.</param>
         /// <param name="property">The property on the control to bind to.</param>
         /// <param name="value">A function which returns the value.</param>
-        public static void Add(StyledElement target, PropertyInfo property, Func<StyledElement, object> value)
+        public static void Add(StyledElement target, PropertyInfo property, Func<StyledElement, object?> value)
         {
             if (target.IsInitialized)
             {
@@ -126,14 +125,14 @@ namespace Avalonia.Markup.Data
 
         private class ClrPropertyValueEntry : Entry
         {
-            public ClrPropertyValueEntry(PropertyInfo property, Func<StyledElement, object> value)
+            public ClrPropertyValueEntry(PropertyInfo property, Func<StyledElement, object?> value)
             {
                 Property = property;
                 Value = value;
             }
 
             public PropertyInfo Property { get; }
-            public Func<StyledElement, object> Value { get; }
+            public Func<StyledElement, object?> Value { get; }
 
             public override void Apply(StyledElement control)
             {
diff --git a/src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs b/src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs
index 21c0d97c74..12440e9450 100644
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs
@@ -6,8 +6,6 @@ using Avalonia.Utilities;
 using System;
 using System.Collections.Generic;
 
-#nullable enable
-
 namespace Avalonia.Markup.Parsers
 {
     internal enum SourceMode
@@ -201,8 +199,8 @@ namespace Avalonia.Markup.Parsers
 
             nodes.Add(new AttachedPropertyNameNode
             {
-                Namespace = ns.ToString(),
-                TypeName = owner.ToString(),
+                Namespace = ns,
+                TypeName = owner,
                 PropertyName = name.ToString()
             });
             return State.AfterMember;
diff --git a/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionObserverBuilder.cs b/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionObserverBuilder.cs
index 97e9698c13..9615057b2c 100644
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionObserverBuilder.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionObserverBuilder.cs
@@ -9,7 +9,7 @@ namespace Avalonia.Markup.Parsers
     internal static class ExpressionObserverBuilder
     {
         [RequiresUnreferencedCode(TrimmingMessages.ReflectionBindingRequiresUnreferencedCodeMessage)]
-        internal static (ExpressionNode Node, SourceMode Mode) Parse(string expression, bool enableValidation = false, Func<string, string, Type>? typeResolver = null,
+        internal static (ExpressionNode Node, SourceMode Mode) Parse(string expression, bool enableValidation = false, Func<string?, string, Type>? typeResolver = null,
             INameScope? nameScope = null)
         {
             if (string.IsNullOrWhiteSpace(expression))
@@ -35,7 +35,7 @@ namespace Avalonia.Markup.Parsers
             string expression,
             bool enableDataValidation = false,
             string? description = null,
-            Func<string, string, Type>? typeResolver = null)
+            Func<string?, string, Type>? typeResolver = null)
         {
             return new ExpressionObserver(
                 root,
@@ -49,7 +49,7 @@ namespace Avalonia.Markup.Parsers
             string expression,
             bool enableDataValidation = false,
             string? description = null,
-            Func<string, string, Type>? typeResolver = null)
+            Func<string?, string, Type>? typeResolver = null)
         {
             _ = rootObservable ?? throw new ArgumentNullException(nameof(rootObservable));
 
@@ -66,7 +66,7 @@ namespace Avalonia.Markup.Parsers
             IObservable<ValueTuple> update,
             bool enableDataValidation = false,
             string? description = null,
-            Func<string, string, Type>? typeResolver = null)
+            Func<string?, string, Type>? typeResolver = null)
         {
             _ = rootGetter ?? throw new ArgumentNullException(nameof(rootGetter));
 
diff --git a/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionParser.cs b/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionParser.cs
index a79d8b3c5f..392d10933f 100644
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionParser.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionParser.cs
@@ -2,8 +2,6 @@ using Avalonia.Data.Core;
 using Avalonia.Markup.Parsers.Nodes;
 using Avalonia.Utilities;
 using System;
-using System.Collections.Generic;
-using System.Linq;
 using Avalonia.Controls;
 using System.Diagnostics.CodeAnalysis;
 
@@ -18,7 +16,7 @@ namespace Avalonia.Markup.Parsers
         private readonly Func<string, string, Type>? _typeResolver;
         private readonly INameScope? _nameScope;
 
-        public ExpressionParser(bool enableValidation, Func<string, string, Type>? typeResolver, INameScope? nameScope)
+        public ExpressionParser(bool enableValidation, Func<string?, string, Type>? typeResolver, INameScope? nameScope)
         {
             _typeResolver = typeResolver;
             _nameScope = nameScope;
@@ -37,13 +35,13 @@ namespace Avalonia.Markup.Parsers
                 ExpressionNode? nextNode = null;
                 switch (astNode)
                 {
-                    case BindingExpressionGrammar.EmptyExpressionNode _:
+                    case BindingExpressionGrammar.EmptyExpressionNode:
                         nextNode = new EmptyExpressionNode();
                         break;
-                    case BindingExpressionGrammar.NotNode _:
+                    case BindingExpressionGrammar.NotNode:
                         nextNode = new LogicalNotNode();
                         break;
-                    case BindingExpressionGrammar.StreamNode _:
+                    case BindingExpressionGrammar.StreamNode:
                         nextNode = new StreamNode();
                         break;
                     case BindingExpressionGrammar.PropertyNameNode propName:
@@ -55,7 +53,7 @@ namespace Avalonia.Markup.Parsers
                     case BindingExpressionGrammar.AttachedPropertyNameNode attachedProp:
                         nextNode = ParseAttachedProperty(attachedProp);
                         break;
-                    case BindingExpressionGrammar.SelfNode _:
+                    case BindingExpressionGrammar.SelfNode:
                         nextNode = new SelfNode();
                         break;
                     case BindingExpressionGrammar.AncestorNode ancestor:
diff --git a/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorGrammar.cs b/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorGrammar.cs
index dbf37f0900..f232d5e109 100644
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorGrammar.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorGrammar.cs
@@ -4,9 +4,7 @@ using System.Linq;
 using Avalonia.Data.Core;
 using Avalonia.Utilities;
 
-#nullable enable
-
-// Don't need to override GetHashCode as the ISyntax objects will not be stored in a hash; the 
+// Don't need to override GetHashCode as the ISyntax objects will not be stored in a hash; the
 // only reason they have overridden Equals methods is for unit testing.
 #pragma warning disable 659
 
@@ -642,7 +640,7 @@ namespace Avalonia.Markup.Parsers
         {
             public override bool Equals(object? obj)
             {
-                return obj is CommaSyntax or;
+                return obj is CommaSyntax;
             }
         }
 
diff --git a/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ControlTemplateTests.cs b/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ControlTemplateTests.cs
index 396a03645c..0a45814efe 100644
--- a/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ControlTemplateTests.cs
+++ b/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ControlTemplateTests.cs
@@ -2,6 +2,7 @@ using System;
 using System.Linq;
 using Avalonia.Controls;
 using Avalonia.Controls.Presenters;
+using Avalonia.Controls.Primitives;
 using Avalonia.Data;
 using Avalonia.Diagnostics;
 using Avalonia.Markup.Xaml.Templates;
@@ -308,6 +309,16 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
             Assert.Equal("Foo", foo.Name);
             Assert.Equal("Bar", bar.Name);
         }
+
+        [Fact]
+        public void ControlTemplate_Can_Be_Empty()
+        {
+            var xaml = "<ControlTemplate xmlns='https://github.com/avaloniaui' />";
+            var template = AvaloniaRuntimeXamlLoader.Parse<ControlTemplate>(xaml);
+
+            var templateResult = template.Build(new TemplatedControl());
+            Assert.Null(templateResult);
+        }
     }
     public class ListBoxHierarchyLine : Panel
     {

From aa55ad23292ba2fb0e4ddff16c02c1e33302c8ba Mon Sep 17 00:00:00 2001
From: Julien Lebosquain <julien@lebosquain.net>
Date: Mon, 20 Mar 2023 12:52:38 +0100
Subject: [PATCH 17/40] Addressed feedback on PR #10608

---
 src/Avalonia.Controls/Carousel.cs                    |  7 +++----
 src/Avalonia.Controls/ComboBox.cs                    |  7 ++-----
 src/Avalonia.Controls/ContextMenu.cs                 |  5 ++---
 src/Avalonia.Controls/ItemsControl.cs                | 12 +++++-------
 src/Avalonia.Controls/ListBox.cs                     |  7 ++-----
 src/Avalonia.Controls/Menu.cs                        |  6 ++----
 src/Avalonia.Controls/MenuItem.cs                    |  5 ++---
 src/Avalonia.Controls/Presenters/ItemsPresenter.cs   | 12 +++++++++---
 src/Avalonia.Controls/Primitives/TabStrip.cs         |  6 ++----
 src/Avalonia.Controls/TabControl.cs                  |  7 ++-----
 src/Avalonia.Controls/Templates/FuncTemplate`1.cs    |  4 ++--
 src/Avalonia.Controls/TreeViewItem.cs                |  4 ++--
 src/Markup/Avalonia.Markup.Xaml/Extensions.cs        |  4 ++--
 .../Markup/Parsers/ExpressionParser.cs               |  6 +++---
 14 files changed, 40 insertions(+), 52 deletions(-)

diff --git a/src/Avalonia.Controls/Carousel.cs b/src/Avalonia.Controls/Carousel.cs
index 84601e8690..1e0405dab4 100644
--- a/src/Avalonia.Controls/Carousel.cs
+++ b/src/Avalonia.Controls/Carousel.cs
@@ -1,7 +1,6 @@
 using Avalonia.Animation;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
-using Avalonia.Controls.Utils;
 
 namespace Avalonia.Controls
 {
@@ -20,8 +19,8 @@ namespace Avalonia.Controls
         /// The default value of <see cref="ItemsControl.ItemsPanelProperty"/> for 
         /// <see cref="Carousel"/>.
         /// </summary>
-        private static readonly ITemplate<Panel> PanelTemplate =
-            new FuncTemplate<Panel>(() => new VirtualizingCarouselPanel());
+        private static readonly FuncTemplate<Panel?> DefaultPanel =
+            new(() => new VirtualizingCarouselPanel());
 
         private IScrollable? _scroller;
 
@@ -31,7 +30,7 @@ namespace Avalonia.Controls
         static Carousel()
         {
             SelectionModeProperty.OverrideDefaultValue<Carousel>(SelectionMode.AlwaysSelected);
-            ItemsPanelProperty.OverrideDefaultValue<Carousel>(PanelTemplate);
+            ItemsPanelProperty.OverrideDefaultValue<Carousel>(DefaultPanel);
         }
 
         /// <summary>
diff --git a/src/Avalonia.Controls/ComboBox.cs b/src/Avalonia.Controls/ComboBox.cs
index f6e4b32d6b..1234b66383 100644
--- a/src/Avalonia.Controls/ComboBox.cs
+++ b/src/Avalonia.Controls/ComboBox.cs
@@ -1,13 +1,10 @@
 using System;
-using System.Diagnostics;
 using System.Linq;
 using Avalonia.Automation.Peers;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Primitives;
-using Avalonia.Controls.Selection;
 using Avalonia.Controls.Shapes;
 using Avalonia.Controls.Templates;
-using Avalonia.Controls.Utils;
 using Avalonia.Input;
 using Avalonia.Interactivity;
 using Avalonia.Layout;
@@ -29,8 +26,8 @@ namespace Avalonia.Controls
         /// <summary>
         /// The default value for the <see cref="ItemsControl.ItemsPanel"/> property.
         /// </summary>
-        private static readonly FuncTemplate<Panel> DefaultPanel =
-            new FuncTemplate<Panel>(() => new VirtualizingStackPanel());
+        private static readonly FuncTemplate<Panel?> DefaultPanel =
+            new(() => new VirtualizingStackPanel());
 
         /// <summary>
         /// Defines the <see cref="IsDropDownOpen"/> property.
diff --git a/src/Avalonia.Controls/ContextMenu.cs b/src/Avalonia.Controls/ContextMenu.cs
index f46594ff96..fc4b11bd4a 100644
--- a/src/Avalonia.Controls/ContextMenu.cs
+++ b/src/Avalonia.Controls/ContextMenu.cs
@@ -4,7 +4,6 @@ using System.ComponentModel;
 using Avalonia.Automation.Peers;
 using System.Linq;
 using Avalonia.Controls.Diagnostics;
-using Avalonia.Controls.Generators;
 using Avalonia.Controls.Platform;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Primitives.PopupPositioning;
@@ -84,8 +83,8 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<Control?> PlacementTargetProperty =
             Popup.PlacementTargetProperty.AddOwner<ContextMenu>();
 
-        private static readonly ITemplate<Panel> DefaultPanel =
-            new FuncTemplate<Panel>(() => new StackPanel { Orientation = Orientation.Vertical });
+        private static readonly FuncTemplate<Panel?> DefaultPanel =
+            new(() => new StackPanel { Orientation = Orientation.Vertical });
         private Popup? _popup;
         private List<Control>? _attachedControls;
         private IInputElement? _previousFocus;
diff --git a/src/Avalonia.Controls/ItemsControl.cs b/src/Avalonia.Controls/ItemsControl.cs
index 4460ff0486..1123f42afa 100644
--- a/src/Avalonia.Controls/ItemsControl.cs
+++ b/src/Avalonia.Controls/ItemsControl.cs
@@ -2,9 +2,7 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Specialized;
-using System.Diagnostics.CodeAnalysis;
 using Avalonia.Automation.Peers;
-using Avalonia.Collections;
 using Avalonia.Controls.Generators;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Presenters;
@@ -29,8 +27,8 @@ namespace Avalonia.Controls
         /// <summary>
         /// The default value for the <see cref="ItemsPanel"/> property.
         /// </summary>
-        private static readonly FuncTemplate<Panel> DefaultPanel =
-            new FuncTemplate<Panel>(() => new StackPanel());
+        private static readonly FuncTemplate<Panel?> DefaultPanel =
+            new(() => new StackPanel());
 
         /// <summary>
         /// Defines the <see cref="Items"/> property.
@@ -58,8 +56,8 @@ namespace Avalonia.Controls
         /// <summary>
         /// Defines the <see cref="ItemsPanel"/> property.
         /// </summary>
-        public static readonly StyledProperty<ITemplate<Panel>> ItemsPanelProperty =
-            AvaloniaProperty.Register<ItemsControl, ITemplate<Panel>>(nameof(ItemsPanel), DefaultPanel);
+        public static readonly StyledProperty<ITemplate<Panel?>> ItemsPanelProperty =
+            AvaloniaProperty.Register<ItemsControl, ITemplate<Panel?>>(nameof(ItemsPanel), DefaultPanel);
 
         /// <summary>
         /// Defines the <see cref="ItemsSource"/> property.
@@ -202,7 +200,7 @@ namespace Avalonia.Controls
         /// <summary>
         /// Gets or sets the panel used to display the items.
         /// </summary>
-        public ITemplate<Panel> ItemsPanel
+        public ITemplate<Panel?> ItemsPanel
         {
             get => GetValue(ItemsPanelProperty);
             set => SetValue(ItemsPanelProperty, value);
diff --git a/src/Avalonia.Controls/ListBox.cs b/src/Avalonia.Controls/ListBox.cs
index 80d1677c2f..e665c2db90 100644
--- a/src/Avalonia.Controls/ListBox.cs
+++ b/src/Avalonia.Controls/ListBox.cs
@@ -1,13 +1,10 @@
 using System.Collections;
-using Avalonia.Controls.Generators;
 using Avalonia.Controls.Metadata;
-using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Selection;
 using Avalonia.Controls.Templates;
 using Avalonia.Input;
 using Avalonia.Input.Platform;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Controls
 {
@@ -20,8 +17,8 @@ namespace Avalonia.Controls
         /// <summary>
         /// The default value for the <see cref="ItemsControl.ItemsPanel"/> property.
         /// </summary>
-        private static readonly FuncTemplate<Panel> DefaultPanel =
-            new FuncTemplate<Panel>(() => new VirtualizingStackPanel());
+        private static readonly FuncTemplate<Panel?> DefaultPanel =
+            new(() => new VirtualizingStackPanel());
 
         /// <summary>
         /// Defines the <see cref="Scroll"/> property.
diff --git a/src/Avalonia.Controls/Menu.cs b/src/Avalonia.Controls/Menu.cs
index dbdcad8217..ac0262c9b2 100644
--- a/src/Avalonia.Controls/Menu.cs
+++ b/src/Avalonia.Controls/Menu.cs
@@ -1,7 +1,6 @@
 using Avalonia.Automation;
 using Avalonia.Automation.Peers;
 using Avalonia.Controls.Platform;
-using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
 using Avalonia.Input;
 using Avalonia.Interactivity;
@@ -14,9 +13,8 @@ namespace Avalonia.Controls
     /// </summary>
     public class Menu : MenuBase, IMainMenu
     {
-        private static readonly ITemplate<Panel> DefaultPanel =
-            new FuncTemplate<Panel>(() => new StackPanel { Orientation = Orientation.Horizontal });
-
+        private static readonly FuncTemplate<Panel?> DefaultPanel =
+            new (() => new StackPanel { Orientation = Orientation.Horizontal });
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Menu"/> class.
diff --git a/src/Avalonia.Controls/MenuItem.cs b/src/Avalonia.Controls/MenuItem.cs
index 03e3444d71..06d84e715d 100644
--- a/src/Avalonia.Controls/MenuItem.cs
+++ b/src/Avalonia.Controls/MenuItem.cs
@@ -4,7 +4,6 @@ using System.Linq;
 using Avalonia.Reactive;
 using System.Windows.Input;
 using Avalonia.Automation.Peers;
-using Avalonia.Controls.Generators;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Mixins;
 using Avalonia.Controls.Primitives;
@@ -107,8 +106,8 @@ namespace Avalonia.Controls
         /// <summary>
         /// The default value for the <see cref="ItemsControl.ItemsPanel"/> property.
         /// </summary>
-        private static readonly ITemplate<Panel> DefaultPanel =
-            new FuncTemplate<Panel>(() => new StackPanel());
+        private static readonly FuncTemplate<Panel?> DefaultPanel =
+            new(() => new StackPanel());
 
         private bool _commandCanExecute = true;
         private bool _commandBindingError;
diff --git a/src/Avalonia.Controls/Presenters/ItemsPresenter.cs b/src/Avalonia.Controls/Presenters/ItemsPresenter.cs
index a0020a0b6e..88d1e10ba4 100644
--- a/src/Avalonia.Controls/Presenters/ItemsPresenter.cs
+++ b/src/Avalonia.Controls/Presenters/ItemsPresenter.cs
@@ -16,7 +16,7 @@ namespace Avalonia.Controls.Presenters
         /// <summary>
         /// Defines the <see cref="ItemsPanel"/> property.
         /// </summary>
-        public static readonly StyledProperty<ITemplate<Panel>> ItemsPanelProperty =
+        public static readonly StyledProperty<ITemplate<Panel?>> ItemsPanelProperty =
             ItemsControl.ItemsPanelProperty.AddOwner<ItemsPresenter>();
 
         private PanelContainerGenerator? _generator;
@@ -68,7 +68,7 @@ namespace Avalonia.Controls.Presenters
         /// <summary>
         /// Gets or sets a template which creates the <see cref="Panel"/> used to display the items.
         /// </summary>
-        public ITemplate<Panel> ItemsPanel
+        public ITemplate<Panel?> ItemsPanel
         {
             get => GetValue(ItemsPanelProperty);
             set => SetValue(ItemsPanelProperty, value);
@@ -166,6 +166,12 @@ namespace Avalonia.Controls.Presenters
                 }
 
                 Panel = ItemsPanel.Build();
+
+                if (Panel is null)
+                {
+                    return;
+                }
+
                 Panel.TemplatedParent = TemplatedParent;
                 Panel.IsItemsHost = true;
                 _scrollSnapPointsInfo = Panel as IScrollSnapPointsInfo;
@@ -183,7 +189,7 @@ namespace Avalonia.Controls.Presenters
                 else
                     CreateSimplePanelGenerator();
 
-                if(Panel is IScrollSnapPointsInfo scrollSnapPointsInfo)
+                if (Panel is IScrollSnapPointsInfo scrollSnapPointsInfo)
                 {
                     scrollSnapPointsInfo.VerticalSnapPointsChanged += (s, e) =>
                     {
diff --git a/src/Avalonia.Controls/Primitives/TabStrip.cs b/src/Avalonia.Controls/Primitives/TabStrip.cs
index b8790d2a44..25cd1cd65b 100644
--- a/src/Avalonia.Controls/Primitives/TabStrip.cs
+++ b/src/Avalonia.Controls/Primitives/TabStrip.cs
@@ -1,15 +1,13 @@
-using Avalonia.Controls.Generators;
 using Avalonia.Controls.Templates;
 using Avalonia.Input;
 using Avalonia.Layout;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Controls.Primitives
 {
     public class TabStrip : SelectingItemsControl
     {
-        private static readonly FuncTemplate<Panel> DefaultPanel =
-            new FuncTemplate<Panel>(() => new WrapPanel { Orientation = Orientation.Horizontal });
+        private static readonly FuncTemplate<Panel?> DefaultPanel =
+            new(() => new WrapPanel { Orientation = Orientation.Horizontal });
 
         static TabStrip()
         {
diff --git a/src/Avalonia.Controls/TabControl.cs b/src/Avalonia.Controls/TabControl.cs
index f12a66a4e6..74cf54beb8 100644
--- a/src/Avalonia.Controls/TabControl.cs
+++ b/src/Avalonia.Controls/TabControl.cs
@@ -1,8 +1,6 @@
-using System.ComponentModel;
 using System.Linq;
 using Avalonia.Collections;
 using Avalonia.Automation.Peers;
-using Avalonia.Controls.Generators;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
@@ -12,7 +10,6 @@ using Avalonia.LogicalTree;
 using Avalonia.VisualTree;
 using Avalonia.Automation;
 using Avalonia.Controls.Metadata;
-using Avalonia.Data;
 
 namespace Avalonia.Controls
 {
@@ -61,8 +58,8 @@ namespace Avalonia.Controls
         /// <summary>
         /// The default value for the <see cref="ItemsControl.ItemsPanel"/> property.
         /// </summary>
-        private static readonly FuncTemplate<Panel> DefaultPanel =
-            new FuncTemplate<Panel>(() => new WrapPanel());
+        private static readonly FuncTemplate<Panel?> DefaultPanel =
+            new(() => new WrapPanel());
 
         /// <summary>
         /// Initializes static members of the <see cref="TabControl"/> class.
diff --git a/src/Avalonia.Controls/Templates/FuncTemplate`1.cs b/src/Avalonia.Controls/Templates/FuncTemplate`1.cs
index 61da607a38..aa8fa43be9 100644
--- a/src/Avalonia.Controls/Templates/FuncTemplate`1.cs
+++ b/src/Avalonia.Controls/Templates/FuncTemplate`1.cs
@@ -7,7 +7,7 @@ namespace Avalonia.Controls.Templates
     /// Creates a control from a <see cref="Func{TControl}"/>.
     /// </summary>
     /// <typeparam name="TControl">The type of control.</typeparam>
-    public class FuncTemplate<TControl> : ITemplate<TControl> where TControl : Control
+    public class FuncTemplate<TControl> : ITemplate<TControl> where TControl : Control?
     {
         private readonly Func<TControl> _func;
 
@@ -31,6 +31,6 @@ namespace Avalonia.Controls.Templates
             return _func();
         }
 
-        object ITemplate.Build() => Build();
+        object? ITemplate.Build() => Build();
     }
 }
diff --git a/src/Avalonia.Controls/TreeViewItem.cs b/src/Avalonia.Controls/TreeViewItem.cs
index 3ac157f727..cf83ba8253 100644
--- a/src/Avalonia.Controls/TreeViewItem.cs
+++ b/src/Avalonia.Controls/TreeViewItem.cs
@@ -40,8 +40,8 @@ namespace Avalonia.Controls
             AvaloniaProperty.RegisterDirect<TreeViewItem, int>(
                 nameof(Level), o => o.Level);
 
-        private static readonly ITemplate<Panel> DefaultPanel =
-            new FuncTemplate<Panel>(() => new StackPanel());
+        private static readonly FuncTemplate<Panel?> DefaultPanel =
+            new(() => new StackPanel());
 
         private TreeView? _treeView;
         private Control? _header;
diff --git a/src/Markup/Avalonia.Markup.Xaml/Extensions.cs b/src/Markup/Avalonia.Markup.Xaml/Extensions.cs
index bbaf6e4074..8d226189dd 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Extensions.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/Extensions.cs
@@ -31,9 +31,9 @@ namespace Avalonia.Markup.Xaml
         [RequiresUnreferencedCode(TrimmingMessages.XamlTypeResolvedRequiresUnreferenceCodeMessage)]
         public static Type ResolveType(this IServiceProvider ctx, string? namespacePrefix, string type)
         {
-            var tr = ctx.GetService<IXamlTypeResolver>();
+            var tr = ctx.GetRequiredService<IXamlTypeResolver>();
             string name = string.IsNullOrEmpty(namespacePrefix) ? type : $"{namespacePrefix}:{type}";
-            return tr?.Resolve(name) ?? throw new XamlLoadException($"Could not find type '{name}'.");
+            return tr.Resolve(name);
         }
         
         public static object? GetDefaultAnchor(this IServiceProvider provider)
diff --git a/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionParser.cs b/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionParser.cs
index 392d10933f..8124d73a3f 100644
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionParser.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionParser.cs
@@ -13,7 +13,7 @@ namespace Avalonia.Markup.Parsers
     internal class ExpressionParser
     {
         private readonly bool _enableValidation;
-        private readonly Func<string, string, Type>? _typeResolver;
+        private readonly Func<string?, string, Type>? _typeResolver;
         private readonly INameScope? _nameScope;
 
         public ExpressionParser(bool enableValidation, Func<string?, string, Type>? typeResolver, INameScope? nameScope)
@@ -88,7 +88,7 @@ namespace Avalonia.Markup.Parsers
             Type? ancestorType = null;
             var ancestorLevel = node.Level;
 
-            if (!(node.Namespace is null) && !(node.TypeName is null))
+            if (!string.IsNullOrEmpty(node.TypeName))
             {
                 if (_typeResolver == null)
                 {
@@ -104,7 +104,7 @@ namespace Avalonia.Markup.Parsers
         private TypeCastNode ParseTypeCastNode(BindingExpressionGrammar.TypeCastNode node)
         {
             Type? castType = null;
-            if (!(node.Namespace is null) && !(node.TypeName is null))
+            if (!string.IsNullOrEmpty(node.TypeName))
             {
                 if (_typeResolver == null)
                 {

From 1e84029a41d56c4cec40d94ec3de2d8fab9c5aee Mon Sep 17 00:00:00 2001
From: Max Katz <maxkatz6@outlook.com>
Date: Fri, 24 Mar 2023 02:37:08 -0400
Subject: [PATCH 18/40] Downgrade Microsoft.CodeAnalysis.CSharp

---
 src/tools/Avalonia.Generators/Avalonia.Generators.csproj | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/tools/Avalonia.Generators/Avalonia.Generators.csproj b/src/tools/Avalonia.Generators/Avalonia.Generators.csproj
index 4ebece583c..88128d6b45 100644
--- a/src/tools/Avalonia.Generators/Avalonia.Generators.csproj
+++ b/src/tools/Avalonia.Generators/Avalonia.Generators.csproj
@@ -9,7 +9,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.4.0" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.9.0" PrivateAssets="all" />
     <PackageReference Include="Microsoft.CodeAnalysis.Analyzers" Version="3.3.4" PrivateAssets="all" />
   </ItemGroup>
 

From 530f176783693e7f06b70d9f8d366ed5e7b50cb5 Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Fri, 24 Mar 2023 21:18:01 +0600
Subject: [PATCH 19/40] Added Rgb24 and Bgr24

---
 .../Media/Imaging/PixelFormatReaders.cs       | 46 ++++++++++++++++++-
 src/Avalonia.Base/Platform/PixelFormat.cs     |  8 +++-
 .../Avalonia.RenderTests/Media/BitmapTests.cs |  2 +
 3 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/src/Avalonia.Base/Media/Imaging/PixelFormatReaders.cs b/src/Avalonia.Base/Media/Imaging/PixelFormatReaders.cs
index fc7c174ed6..c90c4cb5ac 100644
--- a/src/Avalonia.Base/Media/Imaging/PixelFormatReaders.cs
+++ b/src/Avalonia.Base/Media/Imaging/PixelFormatReaders.cs
@@ -228,6 +228,44 @@ static unsafe class PixelFormatReader
 
         public void Reset(IntPtr address) => _address = (Rgba64*)address;
     }
+    
+    public unsafe struct Rgb24PixelFormatReader : IPixelFormatReader
+    {
+        private byte* _address;
+        public Rgba8888Pixel ReadNext()
+        {
+            var addr = _address;
+            _address += 3;
+            return new Rgba8888Pixel
+            {
+                R = addr[0],
+                G = addr[1],
+                B = addr[2],
+                A = 255,
+            };
+        }
+
+        public void Reset(IntPtr address) => _address = (byte*)address;
+    }
+    
+    public unsafe struct Bgr24PixelFormatReader : IPixelFormatReader
+    {
+        private byte* _address;
+        public Rgba8888Pixel ReadNext()
+        {
+            var addr = _address;
+            _address += 3;
+            return new Rgba8888Pixel
+            {
+                R = addr[2],
+                G = addr[1],
+                B = addr[0],
+                A = 255,
+            };
+        }
+
+        public void Reset(IntPtr address) => _address = (byte*)address;
+    }
 
     public static void Transcode(IntPtr dst, IntPtr src, PixelSize size, int strideSrc, int strideDst,
         PixelFormat format)
@@ -242,6 +280,10 @@ static unsafe class PixelFormatReader
             Transcode<Gray8PixelReader>(dst, src, size, strideSrc, strideDst);
         else if (format == PixelFormats.Gray16)
             Transcode<Gray16PixelReader>(dst, src, size, strideSrc, strideDst);
+        else if (format == PixelFormats.Rgb24)
+            Transcode<Rgb24PixelFormatReader>(dst, src, size, strideSrc, strideDst);
+        else if (format == PixelFormats.Bgr24)
+            Transcode<Bgr24PixelFormatReader>(dst, src, size, strideSrc, strideDst);
         else if (format == PixelFormats.Gray32Float)
             Transcode<Gray32FloatPixelReader>(dst, src, size, strideSrc, strideDst);
         else if (format == PixelFormats.Rgba64)
@@ -258,7 +300,9 @@ static unsafe class PixelFormatReader
                || format == PixelFormats.Gray8
                || format == PixelFormats.Gray16
                || format == PixelFormats.Gray32Float
-               || format == PixelFormats.Rgba64;
+               || format == PixelFormats.Rgba64
+               || format == PixelFormats.Bgr24
+               || format == PixelFormats.Rgb24;
     }
     
     public static void Transcode<TReader>(IntPtr dst, IntPtr src, PixelSize size, int strideSrc, int strideDst) where TReader : struct, IPixelFormatReader
diff --git a/src/Avalonia.Base/Platform/PixelFormat.cs b/src/Avalonia.Base/Platform/PixelFormat.cs
index 99fe17055d..95f49bdb25 100644
--- a/src/Avalonia.Base/Platform/PixelFormat.cs
+++ b/src/Avalonia.Base/Platform/PixelFormat.cs
@@ -13,7 +13,9 @@ namespace Avalonia.Platform
         Gray8,
         Gray16,
         Gray32Float,
-        Rgba64
+        Rgba64,
+        Rgb24,
+        Bgr24
     }
 
     public record struct PixelFormat
@@ -35,6 +37,8 @@ namespace Avalonia.Platform
                 else if (FormatEnum == PixelFormatEnum.Rgb565 
                          || FormatEnum == PixelFormatEnum.Gray16)
                     return 16;
+                else if (FormatEnum is PixelFormatEnum.Bgr24 or PixelFormatEnum.Rgb24)
+                    return 24;
                 else if (FormatEnum == PixelFormatEnum.Rgba64)
                     return 64;
 
@@ -70,5 +74,7 @@ namespace Avalonia.Platform
         public static PixelFormat Gray8 { get; } = new PixelFormat(PixelFormatEnum.Gray8);
         public static PixelFormat Gray16 { get; } = new PixelFormat(PixelFormatEnum.Gray16);
         public static PixelFormat Gray32Float { get; } = new PixelFormat(PixelFormatEnum.Gray32Float);
+        public static PixelFormat Rgb24 { get; } = new PixelFormat(PixelFormatEnum.Rgb24);
+        public static PixelFormat Bgr24 { get; } = new PixelFormat(PixelFormatEnum.Bgr24);
     }
 }
diff --git a/tests/Avalonia.RenderTests/Media/BitmapTests.cs b/tests/Avalonia.RenderTests/Media/BitmapTests.cs
index 4ba0c82b87..6916d0c130 100644
--- a/tests/Avalonia.RenderTests/Media/BitmapTests.cs
+++ b/tests/Avalonia.RenderTests/Media/BitmapTests.cs
@@ -143,6 +143,8 @@ namespace Avalonia.Direct2D1.RenderTests.Media
          InlineData(PixelFormatEnum.Gray4),
          InlineData(PixelFormatEnum.Gray8),
          InlineData(PixelFormatEnum.Gray16),
+         InlineData(PixelFormatEnum.Rgb24),
+         InlineData(PixelFormatEnum.Bgr24),
          InlineData(PixelFormatEnum.Gray32Float),
          InlineData(PixelFormatEnum.Rgba64),
          InlineData(PixelFormatEnum.Rgba64, AlphaFormat.Premul),

From f307b7364a164f16c8585cd0a169512f2380e490 Mon Sep 17 00:00:00 2001
From: Benedikt Stebner <Gillibald@users.noreply.github.com>
Date: Fri, 24 Mar 2023 17:33:37 +0100
Subject: [PATCH 20/40] Fix TextLineImp GetTextBounds Fix Tab character
 handling

---
 .../Media/TextFormatting/TextLineImpl.cs      | 17 +++---------
 src/Skia/Avalonia.Skia/TextShaperImpl.cs      |  6 ++---
 .../Media/TextShaperImpl.cs                   | 13 +++++++---
 .../Media/TextFormatting/TextLayoutTests.cs   | 26 ++++++++++++++++++-
 .../Media/TextFormatting/TextLineTests.cs     | 24 +++++++++++++++++
 .../Media/TextFormatting/TextShaperTests.cs   |  6 ++---
 .../HarfBuzzTextShaperImpl.cs                 | 12 ++++++---
 7 files changed, 75 insertions(+), 29 deletions(-)

diff --git a/src/Avalonia.Base/Media/TextFormatting/TextLineImpl.cs b/src/Avalonia.Base/Media/TextFormatting/TextLineImpl.cs
index f426a20b2c..f522ffb5c3 100644
--- a/src/Avalonia.Base/Media/TextFormatting/TextLineImpl.cs
+++ b/src/Avalonia.Base/Media/TextFormatting/TextLineImpl.cs
@@ -697,13 +697,8 @@ namespace Avalonia.Media.TextFormatting
 
                     i = lastRunIndex;
 
-                    if (directionalWidth == 0)
-                    {
-                        continue;
-                    }
-
-                    var coveredLength = 0;
-                    TextBounds? textBounds = null;
+                    int coveredLength;
+                    TextBounds? textBounds;
 
                     switch (currentDirection)
                     {
@@ -831,14 +826,8 @@ namespace Avalonia.Media.TextFormatting
 
                     i = firstRunIndex;
 
-                    if (directionalWidth == 0)
-                    {
-                        continue;
-                    }
-
-                    var coveredLength = 0;
-
                     TextBounds? textBounds = null;
+                    int coveredLength;
 
                     switch (currentDirection)
                     {
diff --git a/src/Skia/Avalonia.Skia/TextShaperImpl.cs b/src/Skia/Avalonia.Skia/TextShaperImpl.cs
index 7d7be46c72..aeb9025ade 100644
--- a/src/Skia/Avalonia.Skia/TextShaperImpl.cs
+++ b/src/Skia/Avalonia.Skia/TextShaperImpl.cs
@@ -26,8 +26,8 @@ namespace Avalonia.Skia
             using (var buffer = new Buffer())
             {
                 // HarfBuzz needs the surrounding characters to correctly shape the text
-                var containingText = GetContainingMemory(text, out var start, out var length);
-                buffer.AddUtf16(containingText.Span, start, length);
+                var containingText = GetContainingMemory(text, out var start, out var length).Span;
+                buffer.AddUtf16(containingText, start, length);
 
                 MergeBreakPair(buffer);
 
@@ -72,7 +72,7 @@ namespace Avalonia.Skia
 
                     var glyphOffset = GetGlyphOffset(glyphPositions, i, textScale);
 
-                    if (i < textSpan.Length && textSpan[i] == '\t')
+                    if (glyphCluster < containingText.Length && containingText[glyphCluster] == '\t')
                     {
                         glyphIndex = typeface.GetGlyph(' ');
 
diff --git a/src/Windows/Avalonia.Direct2D1/Media/TextShaperImpl.cs b/src/Windows/Avalonia.Direct2D1/Media/TextShaperImpl.cs
index 36897d3aff..b881129488 100644
--- a/src/Windows/Avalonia.Direct2D1/Media/TextShaperImpl.cs
+++ b/src/Windows/Avalonia.Direct2D1/Media/TextShaperImpl.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Buffers;
+using System.Collections.Concurrent;
 using System.Globalization;
 using System.Runtime.InteropServices;
 using Avalonia.Media.TextFormatting;
@@ -13,6 +14,8 @@ namespace Avalonia.Direct2D1.Media
 {
     internal class TextShaperImpl : ITextShaperImpl
     {
+        private static readonly ConcurrentDictionary<int, Language> s_cachedLanguage = new();
+
         public ShapedBuffer ShapeText(ReadOnlyMemory<char> text, TextShaperOptions options)
         {
             var textSpan = text.Span;
@@ -24,8 +27,8 @@ namespace Avalonia.Direct2D1.Media
             using (var buffer = new Buffer())
             {
                 // HarfBuzz needs the surrounding characters to correctly shape the text
-                var containingText = GetContainingMemory(text, out var start, out var length);
-                buffer.AddUtf16(containingText.Span, start, length);
+                var containingText = GetContainingMemory(text, out var start, out var length).Span;
+                buffer.AddUtf16(containingText, start, length);
 
                 MergeBreakPair(buffer);
 
@@ -33,7 +36,9 @@ namespace Avalonia.Direct2D1.Media
 
                 buffer.Direction = (bidiLevel & 1) == 0 ? Direction.LeftToRight : Direction.RightToLeft;
 
-                buffer.Language = new Language(culture ?? CultureInfo.CurrentCulture);
+                var usedCulture = culture ?? CultureInfo.CurrentCulture;
+
+                buffer.Language = s_cachedLanguage.GetOrAdd(usedCulture.LCID, _ => new Language(usedCulture));
 
                 var font = ((GlyphTypefaceImpl)typeface).Font;
 
@@ -68,7 +73,7 @@ namespace Avalonia.Direct2D1.Media
 
                     var glyphOffset = GetGlyphOffset(glyphPositions, i, textScale);
 
-                    if (i < textSpan.Length && textSpan[i] == '\t')
+                    if (glyphCluster < containingText.Length && containingText[glyphCluster] == '\t')
                     {
                         glyphIndex = typeface.GetGlyph(' ');
 
diff --git a/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextLayoutTests.cs b/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextLayoutTests.cs
index a24da38fdd..c84fcaaa9a 100644
--- a/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextLayoutTests.cs
+++ b/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextLayoutTests.cs
@@ -1051,7 +1051,7 @@ namespace Avalonia.Skia.UnitTests.Media.TextFormatting
         [InlineData("שנב🧐שנב", 2, 4, FlowDirection.LeftToRight, "11.268,38.208")]
         [InlineData("שנב🧐שנב", 2, 4, FlowDirection.RightToLeft, "11.268,38.208")]
         [Theory]
-        public void Should_HitTextTextRangeBetweenRuns(string text, int start, int length, 
+        public void Should_HitTestTextRangeBetweenRuns(string text, int start, int length, 
             FlowDirection flowDirection, string expected)
         {
             using (Start())
@@ -1087,6 +1087,30 @@ namespace Avalonia.Skia.UnitTests.Media.TextFormatting
             }
         }
 
+        [Fact]
+        public void Should_HitTestTextRangeWithLineBreaks()
+        {
+            using (Start())
+            {
+                var beforeLinebreak = "Line before linebreak";
+                var afterLinebreak = "Line after linebreak";
+                var text = beforeLinebreak + Environment.NewLine + "" + Environment.NewLine + afterLinebreak;
+
+                var textLayout = new TextLayout(text, Typeface.Default, 12, Brushes.Black);
+
+                var end = text.Length - afterLinebreak.Length + 1;
+
+                var rects = textLayout.HitTestTextRange(0, end).ToArray();
+
+                Assert.Equal(3, rects.Length);
+
+                var endX = textLayout.TextLines[2].GetDistanceFromCharacterHit(new CharacterHit(end));
+
+                //First character should be covered
+                Assert.Equal(7.201171875, endX, 2);
+            }
+        }
+
 
         private static IDisposable Start()
         {
diff --git a/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextLineTests.cs b/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextLineTests.cs
index 0cfa78d007..0ddcb2452d 100644
--- a/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextLineTests.cs
+++ b/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextLineTests.cs
@@ -622,6 +622,30 @@ namespace Avalonia.Skia.UnitTests.Media.TextFormatting
             }
         }
 
+        [Fact]
+        public void Should_Get_TextBounds_For_LineBreak()
+        {
+            using (Start())
+            {
+                var defaultProperties = new GenericTextRunProperties(Typeface.Default);
+                var textSource = new SingleBufferTextSource(Environment.NewLine, defaultProperties);
+
+                var formatter = new TextFormatterImpl();
+
+                var textLine =
+                    formatter.FormatLine(textSource, 0, double.PositiveInfinity,
+                        new GenericTextParagraphProperties(defaultProperties));
+
+                var textBounds = textLine.GetTextBounds(0, Environment.NewLine.Length);
+
+                Assert.Equal(1, textBounds.Count);
+
+                Assert.Equal(1, textBounds[0].TextRunBounds.Count);
+
+                Assert.Equal(Environment.NewLine.Length, textBounds[0].TextRunBounds[0].Length);
+            }
+        }
+
         [Fact]
         public void Should_GetTextRange()
         {
diff --git a/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextShaperTests.cs b/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextShaperTests.cs
index 92778793c2..b748f8fc58 100644
--- a/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextShaperTests.cs
+++ b/tests/Avalonia.Skia.UnitTests/Media/TextFormatting/TextShaperTests.cs
@@ -31,11 +31,11 @@ namespace Avalonia.Skia.UnitTests.Media.TextFormatting
         {
             using (Start())
             {
-                var text = "\t";
+                var text = "012345\t";
                 var options = new TextShaperOptions(Typeface.Default.GlyphTypeface, 12, 0, CultureInfo.CurrentCulture, 100);
-                var shapedBuffer = TextShaper.Current.ShapeText(text, options);
+                var shapedBuffer = TextShaper.Current.ShapeText(text.AsMemory().Slice(6), options);
 
-                Assert.Equal(shapedBuffer.Length, text.Length);
+                Assert.Equal(1, shapedBuffer.Length);
                 Assert.Equal(100, shapedBuffer[0].GlyphAdvance);
             }
         }
diff --git a/tests/Avalonia.UnitTests/HarfBuzzTextShaperImpl.cs b/tests/Avalonia.UnitTests/HarfBuzzTextShaperImpl.cs
index 375f87259d..98f188f15a 100644
--- a/tests/Avalonia.UnitTests/HarfBuzzTextShaperImpl.cs
+++ b/tests/Avalonia.UnitTests/HarfBuzzTextShaperImpl.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Buffers;
+using System.Collections.Concurrent;
 using System.Globalization;
 using System.Runtime.InteropServices;
 using Avalonia.Media.TextFormatting;
@@ -13,6 +14,7 @@ namespace Avalonia.UnitTests
 {
     internal class HarfBuzzTextShaperImpl : ITextShaperImpl
     {
+        private static readonly ConcurrentDictionary<int, Language> s_cachedLanguage = new();
         public ShapedBuffer ShapeText(ReadOnlyMemory<char> text, TextShaperOptions options)
         {
             var textSpan = text.Span;
@@ -24,8 +26,8 @@ namespace Avalonia.UnitTests
             using (var buffer = new Buffer())
             {
                 // HarfBuzz needs the surrounding characters to correctly shape the text
-                var containingText = GetContainingMemory(text, out var start, out var length);
-                buffer.AddUtf16(containingText.Span, start, length);
+                var containingText = GetContainingMemory(text, out var start, out var length).Span;
+                buffer.AddUtf16(containingText, start, length);
 
                 MergeBreakPair(buffer);
 
@@ -33,7 +35,9 @@ namespace Avalonia.UnitTests
 
                 buffer.Direction = (bidiLevel & 1) == 0 ? Direction.LeftToRight : Direction.RightToLeft;
 
-                buffer.Language = new Language(culture ?? CultureInfo.CurrentCulture);
+                var usedCulture = culture ?? CultureInfo.CurrentCulture;
+
+                buffer.Language = s_cachedLanguage.GetOrAdd(usedCulture.LCID, _ => new Language(usedCulture));
 
                 var font = ((HarfBuzzGlyphTypefaceImpl)typeface).Font;
 
@@ -68,7 +72,7 @@ namespace Avalonia.UnitTests
 
                     var glyphOffset = GetGlyphOffset(glyphPositions, i, textScale);
 
-                    if (textSpan[i] == '\t')
+                    if (glyphCluster < containingText.Length && containingText[glyphCluster] == '\t')
                     {
                         glyphIndex = typeface.GetGlyph(' ');
 

From 27b2b2733001b3aeee68264d67d8479447fb5aa0 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Fri, 24 Mar 2023 18:14:46 +0100
Subject: [PATCH 21/40] Make ExpandSubTree work again.

---
 src/Avalonia.Controls/TreeView.cs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/Avalonia.Controls/TreeView.cs b/src/Avalonia.Controls/TreeView.cs
index 8f2636a783..1a9042a25b 100644
--- a/src/Avalonia.Controls/TreeView.cs
+++ b/src/Avalonia.Controls/TreeView.cs
@@ -10,6 +10,7 @@ using Avalonia.Controls.Generators;
 using Avalonia.Controls.Primitives;
 using Avalonia.Input;
 using Avalonia.Input.Platform;
+using Avalonia.Layout;
 using Avalonia.Threading;
 using Avalonia.VisualTree;
 
@@ -163,6 +164,9 @@ namespace Avalonia.Controls
         {
             item.IsExpanded = true;
 
+            if (item.Presenter?.Panel is null)
+                (this.GetVisualRoot() as ILayoutRoot)?.LayoutManager.ExecuteLayoutPass();
+
             if (item.Presenter?.Panel is { } panel)
             {
                 foreach (var child in panel.Children)

From a3866201a4ecc56262e7c61072f9056ae91d1df3 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Fri, 24 Mar 2023 18:02:25 +0100
Subject: [PATCH 22/40] Modernized TreeViewTests.

---
 .../TreeViewTests.cs                          | 1975 ++++++-----------
 1 file changed, 721 insertions(+), 1254 deletions(-)

diff --git a/tests/Avalonia.Controls.UnitTests/TreeViewTests.cs b/tests/Avalonia.Controls.UnitTests/TreeViewTests.cs
index 4f533c2f78..9e70e16924 100644
--- a/tests/Avalonia.Controls.UnitTests/TreeViewTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/TreeViewTests.cs
@@ -1,43 +1,35 @@
 using System;
-using System.Collections;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.ComponentModel;
 using System.Linq;
 using Avalonia.Collections;
-using Avalonia.Controls.Generators;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
 using Avalonia.Data.Core;
 using Avalonia.Input;
 using Avalonia.Input.Platform;
-using Avalonia.Interactivity;
+using Avalonia.Layout;
 using Avalonia.LogicalTree;
 using Avalonia.Styling;
 using Avalonia.UnitTests;
-using Moq;
+using Avalonia.VisualTree;
 using Xunit;
 
+#nullable enable
+
 namespace Avalonia.Controls.UnitTests
 {
     public class TreeViewTests
     {
-        MouseTestHelper _mouse = new MouseTestHelper();
+        private readonly MouseTestHelper _mouse = new();
 
         [Fact]
         public void Items_Should_Be_Created()
         {
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                ItemsSource = CreateTestTreeData(),
-            };
-
-            var root = new TestRoot(target);
-
-            CreateNodeDataTemplate(target);
-            ApplyTemplates(target);
+            using var app = Start();
+            var target = CreateTarget();
 
             Assert.Equal(new[] { "Root" }, ExtractItemHeader(target, 0));
             Assert.Equal(new[] { "Child1", "Child2", "Child3" }, ExtractItemHeader(target, 1));
@@ -47,50 +39,31 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Items_Should_Be_Created_Using_ItemTemplate_If_Present()
         {
-            TreeView target;
-
-            var root = new TestRoot
-            {
-                Child = target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = CreateTestTreeData(),
-                    ItemTemplate = new FuncTreeDataTemplate<Node>(
-                        (_, __) => new Canvas(),
-                        x => x.Children),
-                }
-            };
-
-            ApplyTemplates(target);
+            using var app = Start();
+            var itemTemplate = new FuncTreeDataTemplate<Node>(
+                (_, _) => new Canvas(),
+                x => x.Children);
+            var target = CreateTarget(itemTemplate: itemTemplate);
 
             var items = target.GetRealizedTreeContainers()
                 .OfType<TreeViewItem>()
                 .ToList();
 
             Assert.Equal(5, items.Count);
-            Assert.All(items, x => Assert.IsType<Canvas>(x.HeaderPresenter.Child));
+            Assert.All(items, x => Assert.IsType<Canvas>(x.HeaderPresenter?.Child));
         }
 
         [Fact]
         public void Items_Should_Be_Created_Using_ItemConatinerTheme_If_Present()
         {
-            TreeView target;
-            var theme = new ControlTheme(typeof(TreeViewItem));
-
-            var root = new TestRoot
-            {
-                Child = target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = CreateTestTreeData(),
-                    ItemContainerTheme = theme,
-                    ItemTemplate = new FuncTreeDataTemplate<Node>(
-                        (_, __) => new Canvas(),
-                        x => x.Children),
-                }
-            };
+            var theme = CreateTreeViewItemControlTheme();
+            var itemTemplate = new FuncTreeDataTemplate<Node>(
+                (_, _) => new Canvas(),
+                x => x.Children);
 
-            ApplyTemplates(target);
+            var target = CreateTarget(
+                itemContainerTheme: theme,
+                itemTemplate: itemTemplate);
 
             var items = target.GetRealizedTreeContainers()
                 .OfType<TreeViewItem>()
@@ -104,21 +77,12 @@ namespace Avalonia.Controls.UnitTests
         public void Finds_Correct_DataTemplate_When_Application_DataTemplate_Is_Present()
         {
             // #10398
-            using var app = UnitTestApplication.Start();
-            
-            Avalonia.Application.Current.DataTemplates.Add(new FuncDataTemplate<object>((x, _) => new Canvas()));
-            AvaloniaLocator.CurrentMutable.Bind<IGlobalDataTemplates>().ToConstant(Avalonia.Application.Current);
+            using var app = Start();
 
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                ItemsSource = CreateTestTreeData(),
-            };
-
-            var root = new TestRoot(target);
+            Avalonia.Application.Current!.DataTemplates.Add(new FuncDataTemplate<object>((x, _) => new Canvas()));
+            AvaloniaLocator.CurrentMutable.Bind<IGlobalDataTemplates>().ToConstant(Avalonia.Application.Current);
 
-            CreateNodeDataTemplate(target);
-            ApplyTemplates(target);
+            var target = CreateTarget();
 
             Assert.Equal(new[] { "Root" }, ExtractItemHeader(target, 0));
             Assert.Equal(new[] { "Child1", "Child2", "Child3" }, ExtractItemHeader(target, 1));
@@ -128,46 +92,27 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Root_ItemContainerGenerator_Containers_Should_Be_Root_Containers()
         {
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                ItemsSource = CreateTestTreeData(),
-            };
-
-            var root = new TestRoot(target);
-
-            CreateNodeDataTemplate(target);
-            ApplyTemplates(target);
+            using var app = Start();
+            var target = CreateTarget();
 
             var container = (TreeViewItem)target.GetRealizedContainers().Single();
-            var header = (TextBlock)container.HeaderPresenter.Child;
-            Assert.Equal("Root", header.Text);
+            var header = Assert.IsType<TextBlock>(container.HeaderPresenter?.Child);
+            Assert.Equal("Root", header?.Text);
         }
 
         [Fact]
         public void Root_TreeContainerFromItem_Should_Return_Descendant_Item()
         {
-            var tree = CreateTestTreeData();
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                ItemsSource = tree,
-            };
-
-            // For TreeViewItem to find its parent TreeView, OnAttachedToLogicalTree needs
-            // to be called, which requires an IStyleRoot.
-            var root = new TestRoot();
-            root.Child = target;
-
-            CreateNodeDataTemplate(target);
-            ApplyTemplates(target);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
 
-            var container = target.TreeContainerFromItem(tree[0].Children[1].Children[0]);
+            var container = target.TreeContainerFromItem(data[0].Children[1].Children[0]);
 
             Assert.NotNull(container);
 
-            var header = ((TreeViewItem)container).HeaderPresenter;
-            var headerContent = ((TextBlock)header.Child).Text;
+            var header = ((TreeViewItem)container).HeaderPresenter!;
+            var headerContent = ((TextBlock)header.Child!).Text;
 
             Assert.Equal("Grandchild2a", headerContent);
         }
@@ -175,335 +120,192 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Clicking_Item_Should_Select_It()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var item = tree[0].Children[1].Children[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
 
-                Assert.NotNull(container);
+            var item = data[0].Children[1].Children[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
 
-                _mouse.Click(container);
+            _mouse.Click(container);
 
-                Assert.Equal(item, target.SelectedItem);
-                Assert.True(container.IsSelected);
-            }
+            Assert.Equal(item, target.SelectedItem);
+            Assert.True(container.IsSelected);
         }
 
         [Fact]
         public void Clicking_WithControlModifier_Selected_Item_Should_Deselect_It()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var item = tree[0].Children[1].Children[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
 
-                Assert.NotNull(container);
+            var item = data[0].Children[1].Children[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
 
-                target.SelectedItem = item;
+            target.SelectedItem = item;
 
-                Assert.True(container.IsSelected);
+            Assert.True(container.IsSelected);
 
-                _mouse.Click(container, modifiers: KeyModifiers.Control);
+            _mouse.Click(container, modifiers: KeyModifiers.Control);
 
-                Assert.Null(target.SelectedItem);
-                Assert.False(container.IsSelected);
-            }
+            Assert.Null(target.SelectedItem);
+            Assert.False(container.IsSelected);
         }
 
         [Fact]
         public void Clicking_WithControlModifier_Not_Selected_Item_Should_Select_It()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var item1 = tree[0].Children[1].Children[0];
-                var container1 = (TreeViewItem)target.TreeContainerFromItem(item1);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
 
-                var item2 = tree[0].Children[1];
-                var container2 = (TreeViewItem)target.TreeContainerFromItem(item2);
+            var item1 = data[0].Children[1].Children[0];
+            var container1 = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item1));
 
-                Assert.NotNull(container1);
-                Assert.NotNull(container2);
+            var item2 = data[0].Children[1];
+            var container2 = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item2));
 
-                target.SelectedItem = item1;
+            target.SelectedItem = item1;
 
-                Assert.True(container1.IsSelected);
+            Assert.True(container1.IsSelected);
 
-                _mouse.Click(container2, modifiers: KeyModifiers.Control);
+            _mouse.Click(container2, modifiers: KeyModifiers.Control);
 
-                Assert.Equal(item2, target.SelectedItem);
-                Assert.False(container1.IsSelected);
-                Assert.True(container2.IsSelected);
-            }
+            Assert.Equal(item2, target.SelectedItem);
+            Assert.False(container1.IsSelected);
+            Assert.True(container2.IsSelected);
         }
 
         [Fact]
         public void Clicking_WithControlModifier_Selected_Item_Should_Deselect_And_Remove_From_SelectedItems()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                    SelectionMode = SelectionMode.Multiple
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var rootNode = tree[0];
-
-                var item1 = rootNode.Children[0];
-                var item2 = rootNode.Children.Last();
-
-                var item1Container = (TreeViewItem)target.TreeContainerFromItem(item1);
-                var item2Container = (TreeViewItem)target.TreeContainerFromItem(item2);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, multiSelect: true);
+            var rootNode = data[0];
+            var item1 = rootNode.Children[0];
+            var item2 = rootNode.Children.Last();
+            var item1Container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item1));
+            var item2Container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item2));
 
-                ClickContainer(item1Container, KeyModifiers.Control);
-                Assert.True(item1Container.IsSelected);
+            ClickContainer(item1Container, KeyModifiers.Control);
+            Assert.True(item1Container.IsSelected);
 
-                ClickContainer(item2Container, KeyModifiers.Control);
-                Assert.True(item2Container.IsSelected);
+            ClickContainer(item2Container, KeyModifiers.Control);
+            Assert.True(item2Container.IsSelected);
 
-                Assert.Equal(new[] { item1, item2 }, target.SelectedItems.OfType<Node>());
+            Assert.Equal(new[] { item1, item2 }, target.SelectedItems.OfType<Node>());
 
-                ClickContainer(item1Container, KeyModifiers.Control);
-                Assert.False(item1Container.IsSelected);
+            ClickContainer(item1Container, KeyModifiers.Control);
+            Assert.False(item1Container.IsSelected);
 
-                Assert.DoesNotContain(item1, target.SelectedItems.OfType<Node>());
-            }
+            Assert.DoesNotContain(item1, target.SelectedItems.OfType<Node>());
         }
 
         [Fact]
         public void Clicking_WithShiftModifier_DownDirection_Should_Select_Range_Of_Items()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                    SelectionMode = SelectionMode.Multiple
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var rootNode = tree[0];
-
-                var from = rootNode.Children[0];
-                var to = rootNode.Children.Last();
-
-                var fromContainer = (TreeViewItem)target.TreeContainerFromItem(from);
-                var toContainer = (TreeViewItem)target.TreeContainerFromItem(to);
-
-                ClickContainer(fromContainer, KeyModifiers.None);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, multiSelect: true);
+            var rootNode = data[0];
+            var from = rootNode.Children[0];
+            var to = rootNode.Children.Last();
+            var fromContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(from));
+            var toContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(to));
 
-                Assert.True(fromContainer.IsSelected);
+            ClickContainer(fromContainer, KeyModifiers.None);
+            Assert.True(fromContainer.IsSelected);
 
-                ClickContainer(toContainer, KeyModifiers.Shift);
-                AssertChildrenSelected(target, rootNode);
-            }
+            ClickContainer(toContainer, KeyModifiers.Shift);
+            AssertChildrenSelected(target, rootNode);
         }
 
         [Fact]
         public void Clicking_WithShiftModifier_UpDirection_Should_Select_Range_Of_Items()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                    SelectionMode = SelectionMode.Multiple
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var rootNode = tree[0];
-
-                var from = rootNode.Children.Last();
-                var to = rootNode.Children[0];
-
-                var fromContainer = (TreeViewItem)target.TreeContainerFromItem(from);
-                var toContainer = (TreeViewItem)target.TreeContainerFromItem(to);
-
-                ClickContainer(fromContainer, KeyModifiers.None);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, multiSelect: true);
+            var rootNode = data[0];
+            var from = rootNode.Children.Last();
+            var to = rootNode.Children[0];
+            var fromContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(from));
+            var toContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(to));
 
-                Assert.True(fromContainer.IsSelected);
+            ClickContainer(fromContainer, KeyModifiers.None);
+            Assert.True(fromContainer.IsSelected);
 
-                ClickContainer(toContainer, KeyModifiers.Shift);
-                AssertChildrenSelected(target, rootNode);
-            }
+            ClickContainer(toContainer, KeyModifiers.Shift);
+            AssertChildrenSelected(target, rootNode);
         }
 
         [Fact]
         public void Clicking_First_Item_Of_SelectedItems_Should_Select_Only_It()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                    SelectionMode = SelectionMode.Multiple
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var rootNode = tree[0];
-
-                var from = rootNode.Children.Last();
-                var to = rootNode.Children[0];
-
-                var fromContainer = (TreeViewItem)target.TreeContainerFromItem(from);
-                var toContainer = (TreeViewItem)target.TreeContainerFromItem(to);
-
-                ClickContainer(fromContainer, KeyModifiers.None);
-
-                ClickContainer(toContainer, KeyModifiers.Shift);
-                AssertChildrenSelected(target, rootNode);
-
-                ClickContainer(fromContainer, KeyModifiers.None);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, multiSelect: true);
+            var rootNode = data[0];
+            var from = rootNode.Children.Last();
+            var to = rootNode.Children[0];
+            var fromContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(from));
+            var toContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(to));
 
-                Assert.True(fromContainer.IsSelected);
+            ClickContainer(fromContainer, KeyModifiers.None);
+            ClickContainer(toContainer, KeyModifiers.Shift);
+            AssertChildrenSelected(target, rootNode);
 
-                foreach (var child in rootNode.Children)
-                {
-                    if (child == from)
-                    {
-                        continue;
-                    }
+            ClickContainer(fromContainer, KeyModifiers.None);
+            Assert.True(fromContainer.IsSelected);
 
-                    var container = (TreeViewItem)target.TreeContainerFromItem(child);
+            foreach (var child in rootNode.Children)
+            {
+                if (child == from)
+                    continue;
 
-                    Assert.False(container.IsSelected);
-                }
+                var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(child));
+                Assert.False(container.IsSelected);
             }
         }
 
         [Fact]
         public void Double_Clicking_Item_Header_Should_Expand_It()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
 
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
+            CollapseAll(target);
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                CollapseAll(target);
+            var item = data[0].Children[1];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+            var header = container.HeaderPresenter?.Child;
 
-                var item = tree[0].Children[1];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            Assert.False(container.IsExpanded);
+            Assert.NotNull(header);
 
-                Assert.NotNull(container);
-                Assert.False(container.IsExpanded);
-                var header = container.HeaderPresenter.Child;
-                Assert.NotNull(header);
+            _mouse.DoubleClick(header);
 
-                _mouse.DoubleClick(header);
-
-                Assert.True(container.IsExpanded);
-            }
+            Assert.True(container.IsExpanded);
         }
 
         [Fact]
         public void Double_Clicking_Item_Header_With_No_Children_Does_Not_Expand_It()
         {
-            using (Application())
+            using var app = Start();
             {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
+                var data = CreateTestTreeData();
+                var target = CreateTarget(data: data);
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
                 CollapseAll(target);
 
-                var item = tree[0].Children[1].Children[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+                var item = data[0].Children[1].Children[0];
+                var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+                var header = container.HeaderPresenter?.Child;
 
-                Assert.NotNull(container);
                 Assert.False(container.IsExpanded);
-                var header = container.HeaderPresenter.Child;
                 Assert.NotNull(header);
 
                 _mouse.DoubleClick(header);
@@ -515,346 +317,238 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Double_Clicking_Item_Header_Should_Collapse_It()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var item = tree[0].Children[1];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
+            var item = data[0].Children[1];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+            var header = container.HeaderPresenter?.Child;
 
-                Assert.NotNull(container);
-                Assert.True(container.IsExpanded);
-                var header = container.HeaderPresenter.Child;
-                Assert.NotNull(header);
+            Assert.True(container.IsExpanded);
+            Assert.NotNull(header);
 
-                _mouse.DoubleClick(header);
+            _mouse.DoubleClick(header);
 
-                Assert.False(container.IsExpanded);
-            }
+            Assert.False(container.IsExpanded);
         }
 
         [Fact]
         public void Enter_Key_Should_Collapse_TreeViewItem()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target); // NOTE this line
-
-                var item = tree[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
+            var item = data[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+            var header = container.HeaderPresenter?.Child;
 
-                Assert.NotNull(container);
-                Assert.True(container.IsExpanded);
-                var header = container.HeaderPresenter.Child;
-                Assert.NotNull(header);
+            Assert.True(container.IsExpanded);
+            Assert.NotNull(header);
 
-                container.RaiseEvent(new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = Key.Enter,
-                });
+            container.RaiseEvent(new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = Key.Enter,
+            });
 
-                Assert.False(container.IsExpanded);
-            }
+            Assert.False(container.IsExpanded);
         }
 
         [Fact]
-        public void Enter_plus_Ctrl_Key_Should_Collapse_TreeViewItem_Recursively()
+        public void Enter_Plus_Ctrl_Key_Should_Collapse_TreeViewItem_Recursively()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target); // NOTE this line
+            var item = data[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+            var header = container.HeaderPresenter?.Child;
 
-                var item = tree[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            Assert.True(container.IsExpanded);
+            Assert.NotNull(header);
 
-                Assert.NotNull(container);
-                Assert.True(container.IsExpanded);
-                var header = container.HeaderPresenter.Child;
-                Assert.NotNull(header);
+            container.RaiseEvent(new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = Key.Enter,
+                KeyModifiers = KeyModifiers.Control,
+            });
 
-                container.RaiseEvent(new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = Key.Enter,
-                    KeyModifiers = KeyModifiers.Control,
-                });
+            Assert.False(container.IsExpanded);
 
-                Assert.False(container.IsExpanded);
+            AssertEachItemWithChildrenIsCollapsed(item);
 
-                AssertEachItemWithChildrenIsCollapsed(item);
+            void AssertEachItemWithChildrenIsCollapsed(Node node)
+            {
+                var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(node));
 
-                void AssertEachItemWithChildrenIsCollapsed(Node node)
+                if (node.Children?.Count > 0)
                 {
-                    var container = (TreeViewItem)target.TreeContainerFromItem(node);
-                    Assert.NotNull(container);
-                    if (node.Children?.Count > 0)
-                    {
-                        Assert.False(container.IsExpanded);
-                        foreach (var c in node.Children)
-                        {
-                            AssertEachItemWithChildrenIsCollapsed(c);
-                        }
-                    }
-                    else
+                    Assert.False(container.IsExpanded);
+                    foreach (var c in node.Children)
                     {
-                        Assert.True(container.IsExpanded);
+                        AssertEachItemWithChildrenIsCollapsed(c);
                     }
                 }
+                else
+                {
+                    Assert.True(container.IsExpanded);
+                }
             }
         }
 
         [Fact]
         public void Enter_Key_Should_Expand_TreeViewItem()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
 
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
+            CollapseAll(target);
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                CollapseAll(target); // NOTE this line
+            var item = data[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+            var header = container.HeaderPresenter?.Child;
 
-                var item = tree[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            Assert.False(container.IsExpanded);
+            Assert.NotNull(header);
 
-                Assert.NotNull(container);
-                Assert.False(container.IsExpanded);
-                var header = container.HeaderPresenter.Child;
-                Assert.NotNull(header);
-
-                container.RaiseEvent(new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = Key.Enter,
-                });
+            container.RaiseEvent(new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = Key.Enter,
+            });
 
-                Assert.True(container.IsExpanded);
-            }
+            Assert.True(container.IsExpanded);
         }
 
         [Fact]
-        public void Enter_plus_Ctrl_Key_Should_Expand_TreeViewItem_Recursively()
+        public void Enter_Plus_Ctrl_Key_Should_Expand_TreeViewItem_Recursively()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
 
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
+            CollapseAll(target);
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                CollapseAll(target); // NOTE this line
+            var item = data[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+            var header = container.HeaderPresenter?.Child;
 
-                var item = tree[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            Assert.False(container.IsExpanded);
+            Assert.NotNull(header);
 
-                Assert.NotNull(container);
-                Assert.False(container.IsExpanded);
-                var header = container.HeaderPresenter.Child;
-                Assert.NotNull(header);
+            container.RaiseEvent(new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = Key.Enter,
+                KeyModifiers = KeyModifiers.Control,
+            });
 
-                container.RaiseEvent(new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = Key.Enter,
-                    KeyModifiers = KeyModifiers.Control,
-                });
+            Assert.True(container.IsExpanded);
 
-                Assert.True(container.IsExpanded);
+            AssertEachItemWithChildrenIsExpanded(item);
 
-                AssertEachItemWithChildrenIsExpanded(item);
+            void AssertEachItemWithChildrenIsExpanded(Node node)
+            {
+                var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(node));
 
-                void AssertEachItemWithChildrenIsExpanded(Node node)
+                if (node.Children?.Count > 0)
                 {
-                    var container = (TreeViewItem)target.TreeContainerFromItem(node);
-                    Assert.NotNull(container);
-                    if (node.Children?.Count > 0)
+                    Assert.True(container.IsExpanded);
+                    foreach (var c in node.Children)
                     {
-                        Assert.True(container.IsExpanded);
-                        foreach (var c in node.Children)
-                        {
-                            AssertEachItemWithChildrenIsExpanded(c);
-                        }
-                    }
-                    else
-                    {
-                        Assert.False(container.IsExpanded);
+                        AssertEachItemWithChildrenIsExpanded(c);
                     }
                 }
+                else
+                {
+                    Assert.False(container.IsExpanded);
+                }
             }
         }
 
         [Fact]
         public void Space_Key_Should_Collapse_TreeViewItem()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target); // NOTE this line
-
-                var item = tree[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
+            var item = data[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+            var header = container.HeaderPresenter?.Child;
 
-                Assert.NotNull(container);
-                Assert.True(container.IsExpanded);
-                var header = container.HeaderPresenter.Child;
-                Assert.NotNull(header);
+            Assert.True(container.IsExpanded);
+            Assert.NotNull(header);
 
-                container.RaiseEvent(new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = Key.Enter,
-                });
+            container.RaiseEvent(new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = Key.Enter,
+            });
 
-                Assert.False(container.IsExpanded);
-            }
+            Assert.False(container.IsExpanded);
         }
 
         [Fact]
-        public void Space_plus_Ctrl_Key_Should_Collapse_TreeViewItem_Recursively()
+        public void Space_Plus_Ctrl_Key_Should_Collapse_TreeViewItem_Recursively()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target); // NOTE this line
-
-                var item = tree[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
+            var item = data[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+            var header = container.HeaderPresenter?.Child;
 
-                Assert.NotNull(container);
-                Assert.True(container.IsExpanded);
-                var header = container.HeaderPresenter.Child;
-                Assert.NotNull(header);
+            Assert.True(container.IsExpanded);
+            Assert.NotNull(header);
 
-                container.RaiseEvent(new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = Key.Enter,
-                    KeyModifiers = KeyModifiers.Control,
-                });
+            container.RaiseEvent(new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = Key.Enter,
+                KeyModifiers = KeyModifiers.Control,
+            });
 
-                Assert.False(container.IsExpanded);
+            Assert.False(container.IsExpanded);
 
-                AssertEachItemWithChildrenIsCollapsed(item);
+            AssertEachItemWithChildrenIsCollapsed(item);
 
-                void AssertEachItemWithChildrenIsCollapsed(Node node)
+            void AssertEachItemWithChildrenIsCollapsed(Node node)
+            {
+                var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(node));
+                Assert.NotNull(container);
+                if (node.Children?.Count > 0)
                 {
-                    var container = (TreeViewItem)target.TreeContainerFromItem(node);
-                    Assert.NotNull(container);
-                    if (node.Children?.Count > 0)
+                    Assert.False(container.IsExpanded);
+                    foreach (var c in node.Children)
                     {
-                        Assert.False(container.IsExpanded);
-                        foreach (var c in node.Children)
-                        {
-                            AssertEachItemWithChildrenIsCollapsed(c);
-                        }
-                    }
-                    else
-                    {
-                        Assert.True(container.IsExpanded);
+                        AssertEachItemWithChildrenIsCollapsed(c);
                     }
                 }
+                else
+                {
+                    Assert.True(container.IsExpanded);
+                }
             }
         }
 
         [Fact]
         public void Space_Key_Should_Expand_TreeViewItem()
         {
-            using (Application())
+            using var app = Start();
             {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
+                var data = CreateTestTreeData();
+                var target = CreateTarget(data: data);
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                CollapseAll(target); // NOTE this line
+                CollapseAll(target);
 
-                var item = tree[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+                var item = data[0];
+                var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+                var header = container.HeaderPresenter?.Child;
 
-                Assert.NotNull(container);
                 Assert.False(container.IsExpanded);
-                var header = container.HeaderPresenter.Child;
                 Assert.NotNull(header);
 
                 container.RaiseEvent(new KeyEventArgs
@@ -870,281 +564,204 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Space_plus_Ctrl_Key_Should_Expand_TreeViewItem_Recursively()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                CollapseAll(target); // NOTE this line
+            CollapseAll(target);
 
-                var item = tree[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            var item = data[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+            var header = container.HeaderPresenter?.Child;
 
-                Assert.NotNull(container);
-                Assert.False(container.IsExpanded);
-                var header = container.HeaderPresenter.Child;
-                Assert.NotNull(header);
+            Assert.False(container.IsExpanded);
+            Assert.NotNull(header);
 
-                container.RaiseEvent(new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = Key.Enter,
-                    KeyModifiers = KeyModifiers.Control,
-                });
+            container.RaiseEvent(new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = Key.Enter,
+                KeyModifiers = KeyModifiers.Control,
+            });
 
-                Assert.True(container.IsExpanded);
+            Assert.True(container.IsExpanded);
 
-                AssertEachItemWithChildrenIsExpanded(item);
+            AssertEachItemWithChildrenIsExpanded(item);
 
-                void AssertEachItemWithChildrenIsExpanded(Node node)
+            void AssertEachItemWithChildrenIsExpanded(Node node)
+            {
+                var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(node));
+                Assert.NotNull(container);
+                if (node.Children?.Count > 0)
                 {
-                    var container = (TreeViewItem)target.TreeContainerFromItem(node);
-                    Assert.NotNull(container);
-                    if (node.Children?.Count > 0)
+                    Assert.True(container.IsExpanded);
+                    foreach (var c in node.Children)
                     {
-                        Assert.True(container.IsExpanded);
-                        foreach (var c in node.Children)
-                        {
-                            AssertEachItemWithChildrenIsExpanded(c);
-                        }
-                    }
-                    else
-                    {
-                        Assert.False(container.IsExpanded);
+                        AssertEachItemWithChildrenIsExpanded(c);
                     }
                 }
+                else
+                {
+                    Assert.False(container.IsExpanded);
+                }
             }
         }
 
         [Fact]
         public void Numpad_Star_Should_Expand_All_Children_Recursively()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                CollapseAll(target);
+            CollapseAll(target);
 
-                var item = tree[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            var item = data[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
 
-                Assert.NotNull(container);
-                container.RaiseEvent(new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = Key.Multiply,
-                });
+            Assert.NotNull(container);
+            container.RaiseEvent(new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = Key.Multiply,
+            });
 
-                AssertEachItemWithChildrenIsExpanded(item);
+            AssertEachItemWithChildrenIsExpanded(item);
 
-                void AssertEachItemWithChildrenIsExpanded(Node node)
+            void AssertEachItemWithChildrenIsExpanded(Node node)
+            {
+                var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(node));
+                Assert.NotNull(container);
+                if (node.Children?.Count > 0)
                 {
-                    var container = (TreeViewItem)target.TreeContainerFromItem(node);
-                    Assert.NotNull(container);
-                    if (node.Children?.Count > 0)
+                    Assert.True(container.IsExpanded);
+                    foreach (var c in node.Children)
                     {
-                        Assert.True(container.IsExpanded);
-                        foreach (var c in node.Children)
-                        {
-                            AssertEachItemWithChildrenIsExpanded(c);
-                        }
-                    }
-                    else
-                    {
-                        Assert.False(container.IsExpanded);
+                        AssertEachItemWithChildrenIsExpanded(c);
                     }
                 }
+                else
+                {
+                    Assert.False(container.IsExpanded);
+                }
             }
         }
 
         [Fact]
         public void Numpad_Slash_Should_Collapse_All_Children_Recursively()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
+            var item = data[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
 
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
+            Assert.NotNull(container);
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
+            container.RaiseEvent(new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = Key.Divide,
+            });
 
-                var item = tree[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            AssertEachItemWithChildrenIsCollapsed(item);
 
+            void AssertEachItemWithChildrenIsCollapsed(Node node)
+            {
+                var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(node));
                 Assert.NotNull(container);
-                container.RaiseEvent(new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = Key.Divide,
-                });
-
-                AssertEachItemWithChildrenIsCollapsed(item);
-
-                void AssertEachItemWithChildrenIsCollapsed(Node node)
+                if (node.Children?.Count > 0)
                 {
-                    var container = (TreeViewItem)target.TreeContainerFromItem(node);
-                    Assert.NotNull(container);
-                    if (node.Children?.Count > 0)
+                    Assert.False(container.IsExpanded);
+                    foreach (var c in node.Children)
                     {
-                        Assert.False(container.IsExpanded);
-                        foreach (var c in node.Children)
-                        {
-                            AssertEachItemWithChildrenIsCollapsed(c);
-                        }
-                    }
-                    else
-                    {
-                        Assert.True(container.IsExpanded);
+                        AssertEachItemWithChildrenIsCollapsed(c);
                     }
                 }
+                else
+                {
+                    Assert.True(container.IsExpanded);
+                }
             }
         }
 
         [Fact]
         public void Setting_SelectedItem_Should_Set_Container_Selected()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var item = tree[0].Children[1].Children[0];
-                var container = (TreeViewItem)target.TreeContainerFromItem(item);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
+            var item = data[0].Children[1].Children[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
 
-                Assert.NotNull(container);
+            Assert.NotNull(container);
 
-                target.SelectedItem = item;
+            target.SelectedItem = item;
 
-                Assert.True(container.IsSelected);
-            }
+            Assert.True(container.IsSelected);
         }
 
         [Fact]
         public void Setting_SelectedItem_Should_Raise_SelectedItemChanged_Event()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
+            var item = data[0].Children[1].Children[0];
 
-                var item = tree[0].Children[1].Children[0];
+            var called = false;
+            target.SelectionChanged += (s, e) =>
+            {
+                Assert.Empty(e.RemovedItems);
+                Assert.Equal(1, e.AddedItems.Count);
+                Assert.Same(item, e.AddedItems[0]);
+                called = true;
+            };
 
-                var called = false;
-                target.SelectionChanged += (s, e) =>
-                {
-                    Assert.Empty(e.RemovedItems);
-                    Assert.Equal(1, e.AddedItems.Count);
-                    Assert.Same(item, e.AddedItems[0]);
-                    called = true;
-                };
-
-                target.SelectedItem = item;
-                Assert.True(called);
-            }
+            target.SelectedItem = item;
+            Assert.True(called);
         }
 
         [Fact]
         public void Bound_SelectedItem_Should_Not_Be_Cleared_when_Changing_Selection()
         {
-            using (Application())
-            {
-                var dataContext = new TestDataContext();
-
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    DataContext = dataContext
-                };
-
-                target.Bind(TreeView.ItemsSourceProperty, new Binding("Items"));
-                target.Bind(TreeView.SelectedItemProperty, new Binding("SelectedItem"));
+            using var app = Start();
+            var dataContext = new TestDataContext();
+            var target = CreateTarget();
 
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
+            target.DataContext = dataContext;
+            target.Bind(TreeView.ItemsSourceProperty, new Binding("Items"));
+            target.Bind(TreeView.SelectedItemProperty, new Binding("SelectedItem"));
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
+            var selectedValues = new List<object?>();
 
-                var selectedValues = new List<object>();
+            dataContext.PropertyChanged += (_, e) =>
+            {
+                if (e.PropertyName == nameof(TestDataContext.SelectedItem))
+                    selectedValues.Add(dataContext.SelectedItem);
+            };
 
-                dataContext.PropertyChanged += (_, e) =>
-                {
-                    if (e.PropertyName == nameof(TestDataContext.SelectedItem))
-                        selectedValues.Add(dataContext.SelectedItem);
-                };
-                selectedValues.Add(dataContext.SelectedItem);
+            selectedValues.Add(dataContext.SelectedItem);
 
-                _mouse.Click((Interactive)target.Presenter.Panel.Children[0], MouseButton.Left);
-                _mouse.Click((Interactive)target.Presenter.Panel.Children[2], MouseButton.Left);
+            _mouse.Click(target.Presenter!.Panel!.Children[0], MouseButton.Left);
+            _mouse.Click(target.Presenter!.Panel!.Children[2], MouseButton.Left);
 
-                Assert.Equal(3, selectedValues.Count);
-                Assert.Equal(new[] { null, "Item 0", "Item 2" }, selectedValues.ToArray());
-            }
+            Assert.Equal(3, selectedValues.Count);
+            Assert.Equal(new[] { null, "Item 0", "Item 2" }, selectedValues.ToArray());
         }
 
         [Fact]
         public void LogicalChildren_Should_Be_Set()
         {
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                ItemsSource = new[] { "Foo", "Bar", "Baz " },
-            };
+            using var app = Start();
+            var target = CreateTarget(data: null);
 
-            ApplyTemplates(target);
+            target.ItemsSource = new[] { "Foo", "Bar", "Baz " };
+            Layout(target);
 
             var result = target.GetLogicalChildren()
                 .OfType<TreeViewItem>()
-                .Select(x => x.HeaderPresenter.Child)
+                .Select(x => x.HeaderPresenter?.Child)
                 .OfType<TextBlock>()
                 .Select(x => x.Text)
                 .ToList();
@@ -1155,6 +772,7 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void DataContexts_Should_Be_Correctly_Set()
         {
+            using var app = Start();
             var items = new object[]
             {
                 "Foo",
@@ -1163,20 +781,14 @@ namespace Avalonia.Controls.UnitTests
                 new TreeViewItem { Header = "Qux" },
             };
 
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                DataContext = "Base",
-                DataTemplates =
-                {
-                    new FuncDataTemplate<Node>((x, _) => new Button { Content = x })
-                },
-                ItemsSource = items,
-            };
+            var target = CreateTarget();
+            var root = Assert.IsType<TestRoot>(target.GetVisualRoot());
 
-            ApplyTemplates(target);
+            root.DataTemplates.Add(new FuncDataTemplate<Node>((x, _) => new Button { Content = x }));
+            target.DataContext = "Base";
+            target.ItemsSource = items;
 
-            var dataContexts = target.Presenter.Panel.Children
+            var dataContexts = target.Presenter!.Panel!.Children
                 .Cast<Control>()
                 .Select(x => x.DataContext)
                 .ToList();
@@ -1189,37 +801,22 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Control_Item_Should_Not_Be_NameScope()
         {
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                Items =
-                {
-                    new TreeViewItem(),
-                }
-            };
+            using var app = Start();
+            var target = CreateTarget(data: null);
+            var item = new TreeViewItem();
 
-            target.ApplyTemplate();
-            target.Presenter.ApplyTemplate();
+            target.Items!.Add(item);
 
-            var item = target.LogicalChildren[0];
+            Assert.Same(item, target.LogicalChildren[0]);
             Assert.Null(NameScope.GetNameScope((TreeViewItem)item));
         }
 
         [Fact]
         public void Should_React_To_Children_Changing()
         {
+            using var app = Start();
             var data = CreateTestTreeData();
-
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                ItemsSource = data,
-            };
-
-            var root = new TestRoot(target);
-
-            CreateNodeDataTemplate(target);
-            ApplyTemplates(target);
+            var target = CreateTarget(data: data);
 
             Assert.Equal(new[] { "Root" }, ExtractItemHeader(target, 0));
             Assert.Equal(new[] { "Child1", "Child2", "Child3" }, ExtractItemHeader(target, 1));
@@ -1236,7 +833,7 @@ namespace Avalonia.Controls.UnitTests
                 }
             };
 
-            ApplyTemplates(target);
+            Layout(target);
 
             Assert.Equal(new[] { "Root" }, ExtractItemHeader(target, 0));
             Assert.Equal(new[] { "NewChild1" }, ExtractItemHeader(target, 1));
@@ -1245,374 +842,240 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Keyboard_Navigation_Should_Move_To_Last_Selected_Node()
         {
-            using (Application())
-            {
-                var focus = FocusManager.Instance;
-                var navigation = AvaloniaLocator.Current.GetRequiredService<IKeyboardNavigationHandler>();
-                var data = CreateTestTreeData();
+            using var app = Start();
+            var focus = FocusManager.Instance!;
+            var navigation = AvaloniaLocator.Current.GetRequiredService<IKeyboardNavigationHandler>();
+            var data = CreateTestTreeData();
 
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = data,
-                };
+            var target = new TreeView
+            {
+                ItemsSource = data,
+            };
 
-                var button = new Button();
+            var button = new Button();
 
-                var root = new TestRoot
-                {
-                    Child = new StackPanel
-                    {
-                        Children = { target, button },
-                    }
-                };
+            var root = CreateRoot(new StackPanel
+            {
+                Children = { target, button },
+            });
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
+            root.LayoutManager.ExecuteInitialLayoutPass();
+            ExpandAll(target);
 
-                var item = data[0].Children[0];
-                var node = target.TreeContainerFromItem(item);
-                Assert.NotNull(node);
+            var item = data[0].Children[0];
+            var node = target.TreeContainerFromItem(item);
+            Assert.NotNull(node);
 
-                target.SelectedItem = item;
-                node.Focus();
-                Assert.Same(node, focus.Current);
+            target.SelectedItem = item;
+            node.Focus();
+            Assert.Same(node, focus.Current);
 
-                navigation.Move(focus.Current, NavigationDirection.Next);
-                Assert.Same(button, focus.Current);
+            navigation.Move(focus.Current!, NavigationDirection.Next);
+            Assert.Same(button, focus.Current);
 
-                navigation.Move(focus.Current, NavigationDirection.Next);
-                Assert.Same(node, focus.Current);
-            }
+            navigation.Move(focus.Current!, NavigationDirection.Next);
+            Assert.Same(node, focus.Current);
         }
 
         [Fact]
         public void Keyboard_Navigation_Should_Not_Crash_If_Selected_Item_Is_not_In_Tree()
         {
-            using (Application())
-            {
-                var focus = FocusManager.Instance;
-                var data = CreateTestTreeData();
-
-                var selectedNode = new Node { Value = "Out of Tree Selected Item" };
+            using var app = Start();
+            var focus = FocusManager.Instance!;
+            var data = CreateTestTreeData();
 
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = data,
-                    SelectedItem = selectedNode
-                };
+            var selectedNode = new Node { Value = "Out of Tree Selected Item" };
 
-                var button = new Button();
+            var target = new TreeView
+            {
+                Template = CreateTreeViewTemplate(),
+                ItemsSource = data,
+                SelectedItem = selectedNode
+            };
 
-                var root = new TestRoot
-                {
-                    Child = new StackPanel
-                    {
-                        Children = { target, button },
-                    }
-                };
+            var button = new Button();
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
+            var root = CreateRoot(new StackPanel
+            {
+                Children = { target, button },
+            });
 
-                var item = data[0].Children[0];
-                var node = target.TreeContainerFromItem(item);
-                Assert.NotNull(node);
+            root.LayoutManager.ExecuteInitialLayoutPass();
+            ExpandAll(target);
 
-                target.SelectedItem = selectedNode;
-                node.Focus();
-                Assert.Same(node, focus.Current);
+            var item = data[0].Children[0];
+            var node = target.TreeContainerFromItem(item);
+            Assert.NotNull(node);
 
-                var next = KeyboardNavigationHandler.GetNext(node, NavigationDirection.Previous);
-            }
+            target.SelectedItem = selectedNode;
+            node.Focus();
+            Assert.Same(node, focus.Current);
         }
 
         [Fact]
         public void Pressing_SelectAll_Gesture_Should_Select_All_Nodes()
         {
-            using (UnitTestApplication.Start())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                    SelectionMode = SelectionMode.Multiple
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var rootNode = tree[0];
-
-                var keymap = AvaloniaLocator.Current.GetRequiredService<PlatformHotkeyConfiguration>();
-                var selectAllGesture = keymap.SelectAll.First();
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, multiSelect: true);
+            var rootNode = data[0];
+            var keymap = AvaloniaLocator.Current.GetRequiredService<PlatformHotkeyConfiguration>();
+            var selectAllGesture = keymap.SelectAll.First();
 
-                var keyEvent = new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = selectAllGesture.Key,
-                    KeyModifiers = selectAllGesture.KeyModifiers
-                };
+            var keyEvent = new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = selectAllGesture.Key,
+                KeyModifiers = selectAllGesture.KeyModifiers
+            };
 
-                target.RaiseEvent(keyEvent);
+            target.RaiseEvent(keyEvent);
 
-                AssertChildrenSelected(target, rootNode);
-            }
+            AssertChildrenSelected(target, rootNode);
         }
 
         [Fact]
         public void Pressing_SelectAll_Gesture_With_Downward_Range_Selected_Should_Select_All_Nodes()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                    SelectionMode = SelectionMode.Multiple
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var rootNode = tree[0];
-
-                var from = rootNode.Children[0];
-                var to = rootNode.Children.Last();
-
-                var fromContainer = (TreeViewItem)target.TreeContainerFromItem(from);
-                var toContainer = (TreeViewItem)target.TreeContainerFromItem(to);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, multiSelect: true);
+            var rootNode = data[0];
+            var from = rootNode.Children[0];
+            var to = rootNode.Children.Last();
+            var fromContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(from));
+            var toContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(to));
 
-                ClickContainer(fromContainer, KeyModifiers.None);
-                ClickContainer(toContainer, KeyModifiers.Shift);
+            ClickContainer(fromContainer, KeyModifiers.None);
+            ClickContainer(toContainer, KeyModifiers.Shift);
 
-                var keymap = AvaloniaLocator.Current.GetRequiredService<PlatformHotkeyConfiguration>();
-                var selectAllGesture = keymap.SelectAll.First();
+            var keymap = AvaloniaLocator.Current.GetRequiredService<PlatformHotkeyConfiguration>();
+            var selectAllGesture = keymap.SelectAll.First();
 
-                var keyEvent = new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = selectAllGesture.Key,
-                    KeyModifiers = selectAllGesture.KeyModifiers
-                };
+            var keyEvent = new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = selectAllGesture.Key,
+                KeyModifiers = selectAllGesture.KeyModifiers
+            };
 
-                target.RaiseEvent(keyEvent);
+            target.RaiseEvent(keyEvent);
 
-                AssertChildrenSelected(target, rootNode);
-            }
+            AssertChildrenSelected(target, rootNode);
         }
 
         [Fact]
         public void Pressing_SelectAll_Gesture_With_Upward_Range_Selected_Should_Select_All_Nodes()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                    SelectionMode = SelectionMode.Multiple
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                ExpandAll(target);
-
-                var rootNode = tree[0];
-
-                var from = rootNode.Children.Last();
-                var to = rootNode.Children[0];
-
-                var fromContainer = (TreeViewItem)target.TreeContainerFromItem(from);
-                var toContainer = (TreeViewItem)target.TreeContainerFromItem(to);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, multiSelect: true);
+            var rootNode = data[0];
+            var from = rootNode.Children.Last();
+            var to = rootNode.Children[0];
+            var fromContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(from));
+            var toContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(to));
 
-                ClickContainer(fromContainer, KeyModifiers.None);
-                ClickContainer(toContainer, KeyModifiers.Shift);
+            ClickContainer(fromContainer, KeyModifiers.None);
+            ClickContainer(toContainer, KeyModifiers.Shift);
 
-                var keymap = AvaloniaLocator.Current.GetRequiredService<PlatformHotkeyConfiguration>();
-                var selectAllGesture = keymap.SelectAll.First();
+            var keymap = AvaloniaLocator.Current.GetRequiredService<PlatformHotkeyConfiguration>();
+            var selectAllGesture = keymap.SelectAll.First();
 
-                var keyEvent = new KeyEventArgs
-                {
-                    RoutedEvent = InputElement.KeyDownEvent,
-                    Key = selectAllGesture.Key,
-                    KeyModifiers = selectAllGesture.KeyModifiers
-                };
+            var keyEvent = new KeyEventArgs
+            {
+                RoutedEvent = InputElement.KeyDownEvent,
+                Key = selectAllGesture.Key,
+                KeyModifiers = selectAllGesture.KeyModifiers
+            };
 
-                target.RaiseEvent(keyEvent);
+            target.RaiseEvent(keyEvent);
 
-                AssertChildrenSelected(target, rootNode);
-            }
+            AssertChildrenSelected(target, rootNode);
         }
 
         [Fact]
         public void Right_Click_On_SelectedItem_Should_Not_Clear_Existing_Selection()
         {
-            using (UnitTestApplication.Start())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                    SelectionMode = SelectionMode.Multiple,
-                };
-                AvaloniaLocator.CurrentMutable.Bind<PlatformHotkeyConfiguration>().ToConstant(new Mock<PlatformHotkeyConfiguration>().Object);
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, multiSelect: true);
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                target.ExpandSubTree((TreeViewItem)target.Presenter.Panel.Children[0]);
-                target.SelectAll();
+            target.SelectAll();
 
-                AssertChildrenSelected(target, tree[0]);
-                Assert.Equal(5, target.SelectedItems.Count);
+            AssertChildrenSelected(target, data[0]);
+            Assert.Equal(5, target.SelectedItems.Count);
 
-                _mouse.Click((Interactive)target.Presenter.Panel.Children[0], MouseButton.Right);
+            _mouse.Click(target.Presenter!.Panel!.Children[0], MouseButton.Right);
 
-                Assert.Equal(5, target.SelectedItems.Count);
-            }
+            Assert.Equal(5, target.SelectedItems.Count);
         }
 
         [Fact]
         public void Right_Click_On_UnselectedItem_Should_Clear_Existing_Selection()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                    SelectionMode = SelectionMode.Multiple,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                target.ExpandSubTree((TreeViewItem)target.Presenter.Panel.Children[0]);
-
-                var rootNode = tree[0];
-                var to = rootNode.Children[0];
-                var then = rootNode.Children[1];
-
-                var fromContainer = (TreeViewItem)target.TreeContainerFromItem(rootNode);
-                var toContainer = (TreeViewItem)target.TreeContainerFromItem(to);
-                var thenContainer = (TreeViewItem)target.TreeContainerFromItem(then);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, multiSelect: true);
+            var rootNode = data[0];
+            var to = rootNode.Children[0];
+            var then = rootNode.Children[1];
+            var fromContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(rootNode));
+            var toContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(to));
+            var thenContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(then));
 
-                ClickContainer(fromContainer, KeyModifiers.None);
-                ClickContainer(toContainer, KeyModifiers.Shift);
+            ClickContainer(fromContainer, KeyModifiers.None);
+            ClickContainer(toContainer, KeyModifiers.Shift);
 
-                Assert.Equal(2, target.SelectedItems.Count);
+            Assert.Equal(2, target.SelectedItems.Count);
 
-                _mouse.Click(thenContainer, MouseButton.Right);
+            _mouse.Click(thenContainer, MouseButton.Right);
 
-                Assert.Equal(1, target.SelectedItems.Count);
-            }
+            Assert.Equal(1, target.SelectedItems.Count);
         }
 
         [Fact]
         public void Shift_Right_Click_Should_Not_Select_Multiple()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                    SelectionMode = SelectionMode.Multiple,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                target.ExpandSubTree((TreeViewItem)target.Presenter.Panel.Children[0]);
-
-                var rootNode = tree[0];
-                var from = rootNode.Children[0];
-                var to = rootNode.Children[1];
-                var fromContainer = (TreeViewItem)target.TreeContainerFromItem(from);
-                var toContainer = (TreeViewItem)target.TreeContainerFromItem(to);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, multiSelect: true);
+            var rootNode = data[0];
+            var from = rootNode.Children[0];
+            var to = rootNode.Children[1];
+            var fromContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(from));
+            var toContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(to));
 
-                _mouse.Click(fromContainer);
-                _mouse.Click(toContainer, MouseButton.Right, modifiers: KeyModifiers.Shift);
+            _mouse.Click(fromContainer);
+            _mouse.Click(toContainer, MouseButton.Right, modifiers: KeyModifiers.Shift);
 
-                Assert.Equal(1, target.SelectedItems.Count);
-            }
+            Assert.Equal(1, target.SelectedItems.Count);
         }
 
         [Fact]
         public void Ctrl_Right_Click_Should_Not_Select_Multiple()
         {
-            using (Application())
-            {
-                var tree = CreateTestTreeData();
-                var target = new TreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    ItemsSource = tree,
-                    SelectionMode = SelectionMode.Multiple,
-                };
-
-                var visualRoot = new TestRoot();
-                visualRoot.Child = target;
-
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
-                target.ExpandSubTree((TreeViewItem)target.Presenter.Panel.Children[0]);
-
-                var rootNode = tree[0];
-                var from = rootNode.Children[0];
-                var to = rootNode.Children[1];
-                var fromContainer = (TreeViewItem)target.TreeContainerFromItem(from);
-                var toContainer = (TreeViewItem)target.TreeContainerFromItem(to);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, multiSelect: true);
+            var rootNode = data[0];
+            var from = rootNode.Children[0];
+            var to = rootNode.Children[1];
+            var fromContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(from));
+            var toContainer = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(to));
 
-                _mouse.Click(fromContainer);
-                _mouse.Click(toContainer, MouseButton.Right, modifiers: KeyModifiers.Control);
+            _mouse.Click(fromContainer);
+            _mouse.Click(toContainer, MouseButton.Right, modifiers: KeyModifiers.Control);
 
-                Assert.Equal(1, target.SelectedItems.Count);
-            }
+            Assert.Equal(1, target.SelectedItems.Count);
         }
 
         [Fact]
         public void TreeViewItems_Level_Should_Be_Set()
         {
-            var tree = CreateTestTreeData();
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                ItemsSource = tree,
-            };
-
-            var visualRoot = new TestRoot();
-            visualRoot.Child = target;
-
-            CreateNodeDataTemplate(target);
-            ApplyTemplates(target);
-            ExpandAll(target);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
 
             Assert.Equal(0, GetItem(target, 0).Level);
             Assert.Equal(1, GetItem(target, 0, 0).Level);
@@ -1624,6 +1087,7 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void TreeViewItems_Level_Should_Be_Set_For_Derived_TreeView()
         {
+            using var app = Start();
             var tree = CreateTestTreeData();
             var target = new DerivedTreeView
             {
@@ -1631,11 +1095,8 @@ namespace Avalonia.Controls.UnitTests
                 ItemsSource = tree,
             };
 
-            var visualRoot = new TestRoot();
-            visualRoot.Child = target;
-
-            CreateNodeDataTemplate(target);
-            ApplyTemplates(target);
+            var root = CreateRoot(target);
+            root.LayoutManager.ExecuteInitialLayoutPass();
             ExpandAll(target);
 
             Assert.Equal(0, GetItem(target, 0).Level);
@@ -1649,29 +1110,15 @@ namespace Avalonia.Controls.UnitTests
         public void Adding_Node_To_Removed_And_ReAdded_Parent_Should_Not_Crash()
         {
             // Issue #2985
-            var tree = CreateTestTreeData();
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                ItemsSource = tree,
-            };
-
-            var visualRoot = new TestRoot();
-            visualRoot.Child = target;
-
-            CreateNodeDataTemplate(target);
-            ApplyTemplates(target);
-            ExpandAll(target);
-
-            var parent = tree[0];
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
+            var parent = data[0];
             var node = parent.Children[1];
 
             parent.Children.Remove(node);
             parent.Children.Add(node);
 
-            var item = target.TreeContainerFromItem(node);
-            ApplyTemplates(new[] { item });
-
             // #2985 causes ArgumentException here.
             node.Children.Add(new Node());
         }
@@ -1680,101 +1127,69 @@ namespace Avalonia.Controls.UnitTests
         public void Auto_Expanding_In_Style_Should_Not_Break_Range_Selection()
         {
             // Issue #2980.
-            using (Application())
+            using var app = Start();
+
+            var data = new List<Node>
             {
-                var target = new DerivedTreeView
-                {
-                    Template = CreateTreeViewTemplate(),
-                    SelectionMode = SelectionMode.Multiple,
-                    ItemsSource = new List<Node>
-                    {
-                        new Node { Value = "Root1", },
-                        new Node { Value = "Root2", },
-                    },
-                };
+                new Node { Value = "Root1", },
+                new Node { Value = "Root2", },
+            };
 
-                var visualRoot = new TestRoot
+            var style = new Style(x => x.OfType<TreeViewItem>())
+            {
+                Setters =
                 {
-                    Styles =
-                    {
-                        new Style(x => x.OfType<TreeViewItem>())
-                        {
-                            Setters =
-                            {
-                                new Setter(TreeViewItem.IsExpandedProperty, true),
-                            },
-                        },
-                    },
-                    Child = target,
-                };
+                    new Setter(TreeViewItem.IsExpandedProperty, true),
+                },
+            };
 
-                CreateNodeDataTemplate(target);
-                ApplyTemplates(target);
+            var target = CreateTarget(data: data, styles: new[] { style }, multiSelect: true);
 
-                _mouse.Click(GetItem(target, 0));
-                _mouse.Click(GetItem(target, 1), modifiers: KeyModifiers.Shift);
-            }
+            _mouse.Click(GetItem(target, 0));
+            _mouse.Click(GetItem(target, 1), modifiers: KeyModifiers.Shift);
         }
 
         [Fact]
         public void Removing_TreeView_From_Root_Should_Preserve_TreeViewItems()
         {
             // Issue #3328
-            var tree = CreateTestTreeData();
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                ItemsSource = tree,
-            };
-
-            var root = new TestRoot();
-            root.Child = target;
-
-            CreateNodeDataTemplate(target);
-            ApplyTemplates(target);
-            ExpandAll(target);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
+            var root = Assert.IsType<TestRoot>(target.GetVisualRoot());
 
             Assert.Equal(5, target.GetRealizedTreeContainers().Count());
 
             root.Child = null;
 
             Assert.Equal(5, target.GetRealizedTreeContainers().Count());
-            Assert.Equal(1, target.Presenter.Panel.Children.Count);
+            Assert.Equal(1, target.Presenter!.Panel!.Children.Count);
 
             var rootNode = Assert.IsType<TreeViewItem>(target.Presenter.Panel.Children[0]);
             Assert.Equal(3, rootNode.GetRealizedContainers().Count());
-            Assert.Equal(3, rootNode.Presenter.Panel.Children.Count);
+            Assert.Equal(3, rootNode.Presenter!.Panel!.Children.Count);
 
             var child2Node = Assert.IsType<TreeViewItem>(rootNode.Presenter.Panel.Children[1]);
             Assert.Equal(1, child2Node.GetRealizedContainers().Count());
-            Assert.Equal(1, child2Node.Presenter.Panel.Children.Count);
+            Assert.Equal(1, child2Node.Presenter!.Panel!.Children.Count);
         }
 
         [Fact]
         public void Clearing_TreeView_Items_Clears_Index()
         {
             // Issue #3551
-            var tree = CreateTestTreeData();
-            var target = new TreeView
-            {
-                Template = CreateTreeViewTemplate(),
-                ItemsSource = tree,
-            };
-
-            var root = new TestRoot();
-            root.Child = target;
-
-            CreateNodeDataTemplate(target);
-            ApplyTemplates(target);
-
-            var rootNode = tree[0];
-            var container = (TreeViewItem)target.TreeContainerFromItem(rootNode);
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
+            var root = Assert.IsType<TestRoot>(target.GetVisualRoot());
+            var rootNode = data[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(rootNode));
 
             Assert.NotNull(container);
 
             root.Child = null;
 
-            tree.Clear();
+            data.Clear();
 
             Assert.Empty(target.GetRealizedContainers());
         }
@@ -1789,7 +1204,9 @@ namespace Avalonia.Controls.UnitTests
                 ItemsSource = tree,
             };
 
-            ApplyTemplates(target);
+            var root = CreateRoot(target);
+            root.LayoutManager.ExecuteInitialLayoutPass();
+            ExpandAll(target);
 
             // Verify that all items are DerivedTreeViewItem
             foreach (var container in target.GetRealizedTreeContainers())
@@ -1798,39 +1215,54 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
-        private void ApplyTemplates(TreeView tree)
+        private static TreeView CreateTarget(Optional<IList<Node>?> data = default,
+            bool expandAll = true,
+            ControlTheme? itemContainerTheme = null,
+            IDataTemplate? itemTemplate = null,
+            bool multiSelect = false,
+            IEnumerable<Style>? styles = null)
         {
-            tree.ApplyTemplate();
-            tree.Presenter.ApplyTemplate();
-            ApplyTemplates(tree.Presenter.Panel.Children);
-        }
+            var target = new TreeView
+            {
+                ItemContainerTheme = itemContainerTheme,
+                ItemsSource = data.HasValue ? data.Value : CreateTestTreeData(),
+                ItemTemplate = itemTemplate,
+                SelectionMode = multiSelect ? SelectionMode.Multiple : SelectionMode.Single,
+            };
 
-        private void ApplyTemplates(IEnumerable<Control> controls)
-        {
-            foreach (TreeViewItem control in controls)
+            var root = CreateRoot(target);
+
+            if (styles is not null)
+                root.Styles.AddRange(styles);
+
+            root.LayoutManager.ExecuteInitialLayoutPass();
+
+            if (expandAll)
             {
-                control.Template = CreateTreeViewItemTemplate();
-                control.ApplyTemplate();
-                control.Presenter.ApplyTemplate();
-                ((ContentPresenter)control.HeaderPresenter).UpdateChild();
-                ApplyTemplates(control.Presenter.Panel.Children);
+                ExpandAll(target);
             }
+
+            return target;
         }
 
-        private TreeViewItem GetItem(TreeView target, params int[] indexes)
+        private static TestRoot CreateRoot(Control child)
         {
-            var c = (ItemsControl)target;
-
-            foreach (var index in indexes)
+            return new TestRoot
             {
-                var item = c.ItemsView[index];
-                c = (ItemsControl)target.TreeContainerFromItem(item);
-            }
-
-            return (TreeViewItem)c;
+                Resources =
+                {
+                    { typeof(TreeView), CreateTreeViewControlTheme() },
+                    { typeof(TreeViewItem), CreateTreeViewItemControlTheme() },
+                },
+                DataTemplates =
+                {
+                    new TestTreeDataTemplate(),
+                },
+                Child = child,
+            };
         }
 
-        private AvaloniaList<Node> CreateTestTreeData()
+        private static AvaloniaList<Node> CreateTestTreeData()
         {
             return new AvaloniaList<Node>
             {
@@ -1863,12 +1295,29 @@ namespace Avalonia.Controls.UnitTests
             };
         }
 
-        private void CreateNodeDataTemplate(Control control)
+        private static ControlTheme CreateTreeViewControlTheme()
+        {
+            return new ControlTheme(typeof(TreeView))
+            {
+                Setters =
+                {
+                    new Setter(TreeView.TemplateProperty, CreateTreeViewTemplate()),
+                },
+            };
+        }
+
+        private static ControlTheme CreateTreeViewItemControlTheme()
         {
-            control.DataTemplates.Add(new TestTreeDataTemplate());
+            return new ControlTheme(typeof(TreeViewItem))
+            {
+                Setters =
+                {
+                    new Setter(TreeView.TemplateProperty, CreateTreeViewItemTemplate()),
+                },
+            };
         }
 
-        private IControlTemplate CreateTreeViewTemplate()
+        private static IControlTemplate CreateTreeViewTemplate()
         {
             return new FuncControlTemplate<TreeView>((parent, scope) => new ItemsPresenter
             {
@@ -1876,7 +1325,7 @@ namespace Avalonia.Controls.UnitTests
             }.RegisterInNameScope(scope));
         }
 
-        private IControlTemplate CreateTreeViewItemTemplate()
+        private static IControlTemplate CreateTreeViewItemTemplate()
         {
             return new FuncControlTemplate<TreeViewItem>((parent, scope) => new Panel
             {
@@ -1895,12 +1344,13 @@ namespace Avalonia.Controls.UnitTests
                     new ItemsPresenter
                     {
                         Name = "PART_ItemsPresenter",
+                        [~ItemsPresenter.IsVisibleProperty] = parent[~TreeViewItem.IsExpandedProperty],
                     }.RegisterInNameScope(scope)
                 }
             });
         }
 
-        private void ExpandAll(TreeView tree)
+        private static void ExpandAll(TreeView tree)
         {
             foreach (var i in tree.GetRealizedContainers())
             {
@@ -1908,7 +1358,7 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
-        private void CollapseAll(TreeView tree)
+        private static void CollapseAll(TreeView tree)
         {
             foreach (var i in tree.GetRealizedContainers())
             {
@@ -1916,32 +1366,44 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
-        private List<string> ExtractItemHeader(TreeView tree, int level)
+        private static TreeViewItem GetItem(TreeView target, params int[] indexes)
+        {
+            var c = (ItemsControl)target;
+
+            foreach (var index in indexes)
+            {
+                var item = c.ItemsView[index]!;
+                c = (ItemsControl)target.TreeContainerFromItem(item)!;
+            }
+
+            return (TreeViewItem)c;
+        }
+
+        private static List<string?> ExtractItemHeader(TreeView tree, int level)
         {
-            return ExtractItemContent(tree.Presenter.Panel, 0, level)
-                .Select(x => x.HeaderPresenter.Child)
+            return ExtractItemContent(tree.Presenter?.Panel, 0, level)
+                .Select(x => x.HeaderPresenter?.Child)
                 .OfType<TextBlock>()
                 .Select(x => x.Text)
                 .ToList();
         }
 
-        private IEnumerable<TreeViewItem> ExtractItemContent(Panel panel, int currentLevel, int level)
+        private static IEnumerable<TreeViewItem> ExtractItemContent(Panel? panel, int currentLevel, int level)
         {
-            foreach (TreeViewItem container in panel.Children)
+            if (panel is null)
+                yield break;
+
+            foreach (var c in panel.Children)
             {
-                if (container.Template == null)
-                {
-                    container.Template = CreateTreeViewItemTemplate();
-                    container.ApplyTemplate();
-                }
+                var container = Assert.IsType<TreeViewItem>(c);
 
                 if (currentLevel == level)
                 {
                     yield return container;
                 }
-                else
+                else if (container.Presenter?.Panel is { } childPanel)
                 {
-                    foreach (var child in ExtractItemContent(container.Presenter.Panel, currentLevel + 1, level))
+                    foreach (var child in ExtractItemContent(childPanel, currentLevel + 1, level))
                     {
                         yield return child;
                     }
@@ -1949,6 +1411,11 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        private void Layout(Control c)
+        {
+            (c.GetVisualRoot() as ILayoutRoot)?.LayoutManager.ExecuteLayoutPass();
+        }
+
         private void ClickContainer(Control container, KeyModifiers modifiers)
         {
             _mouse.Click(container, modifiers: modifiers);
@@ -1956,37 +1423,37 @@ namespace Avalonia.Controls.UnitTests
 
         private void AssertChildrenSelected(TreeView treeView, Node rootNode)
         {
+            Assert.NotNull(rootNode.Children);
+
             foreach (var child in rootNode.Children)
             {
-                var container = (TreeViewItem)treeView.TreeContainerFromItem(child);
-
+                var container = Assert.IsType<TreeViewItem>(treeView.TreeContainerFromItem(child));
                 Assert.True(container.IsSelected);
             }
         }
 
-        private IDisposable Application()
+        private IDisposable Start()
         {
             return UnitTestApplication.Start(
                 TestServices.MockThreadingInterface.With(
                     focusManager: new FocusManager(),
+                    fontManagerImpl: new MockFontManagerImpl(),
                     keyboardDevice: () => new KeyboardDevice(),
                     keyboardNavigation: new KeyboardNavigationHandler(),
-                    inputManager: new InputManager()));
+                    inputManager: new InputManager(),
+                    renderInterface: new MockPlatformRenderInterface(),
+                    textShaperImpl: new MockTextShaperImpl()));
         }
 
         private class Node : NotifyingBase
         {
-            private IAvaloniaList<Node> _children;
+            private IAvaloniaList<Node> _children = new AvaloniaList<Node>();
 
-            public string Value { get; set; }
+            public string? Value { get; set; }
 
             public IAvaloniaList<Node> Children
             {
-                get
-                {
-                    return _children;
-                }
-
+                get => _children;
                 set
                 {
                     _children = value;
@@ -1997,19 +1464,19 @@ namespace Avalonia.Controls.UnitTests
 
         private class TestTreeDataTemplate : ITreeDataTemplate
         {
-            public Control Build(object param)
+            public Control Build(object? param)
             {
-                var node = (Node)param;
+                var node = (Node)param!;
                 return new TextBlock { Text = node.Value };
             }
 
             public InstancedBinding ItemsSelector(object item)
             {
-                var obs = ExpressionObserver.Create(item, o => (o as Node).Children);
+                var obs = ExpressionObserver.Create(item, o => ((Node)o).Children);
                 return InstancedBinding.OneWay(obs);
             }
 
-            public bool Match(object data)
+            public bool Match(object? data)
             {
                 return data is Node;
             }
@@ -2030,16 +1497,16 @@ namespace Avalonia.Controls.UnitTests
 
         private class TestDataContext : INotifyPropertyChanged
         {
-            private string _selectedItem;
+            private string? _selectedItem;
 
             public TestDataContext()
             {
                 Items = new ObservableCollection<string>(Enumerable.Range(0, 5).Select(i => $"Item {i}"));
             }
 
-            public ObservableCollection<string> Items { get; }
+            public ObservableCollection<string>? Items { get; }
 
-            public string SelectedItem
+            public string? SelectedItem
             {
                 get { return _selectedItem; }
                 set
@@ -2049,7 +1516,7 @@ namespace Avalonia.Controls.UnitTests
                 }
             }
 
-            public event PropertyChangedEventHandler PropertyChanged;
+            public event PropertyChangedEventHandler? PropertyChanged;
 
         }
     }

From 8c1d4fbbbfdd453506eae7c64ead584852562ec3 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Fri, 24 Mar 2023 18:20:20 +0100
Subject: [PATCH 23/40] Added failing test for treeview selection.

---
 .../TreeViewTests.cs                            | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/tests/Avalonia.Controls.UnitTests/TreeViewTests.cs b/tests/Avalonia.Controls.UnitTests/TreeViewTests.cs
index 9e70e16924..129720d00a 100644
--- a/tests/Avalonia.Controls.UnitTests/TreeViewTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/TreeViewTests.cs
@@ -750,6 +750,23 @@ namespace Avalonia.Controls.UnitTests
             Assert.Equal(new[] { null, "Item 0", "Item 2" }, selectedValues.ToArray());
         }
 
+        [Fact]
+        public void Expanding_SelectedItem_To_Be_Visible_Should_Result_In_Selected_Container()
+        {
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data, expandAll: false);
+            
+            target.SelectedItem = data[0].Children[1];
+
+            var rootItem = Assert.IsType<TreeViewItem>(target.ContainerFromIndex(0));
+            rootItem.IsExpanded = true;
+            Layout(target);
+
+            var container = Assert.IsType<TreeViewItem>(rootItem.ContainerFromIndex(1));
+            Assert.True(container.IsSelected);
+        }
+
         [Fact]
         public void LogicalChildren_Should_Be_Set()
         {

From c2b83d9909f341d7aac37bd15ae26e0d2407d882 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Fri, 24 Mar 2023 18:42:46 +0100
Subject: [PATCH 24/40] Defer TreeViewItem creation to TreeView.

Fixes nodes not being selected correctly when parent node is expanded.
---
 src/Avalonia.Controls/TreeViewItem.cs | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/Avalonia.Controls/TreeViewItem.cs b/src/Avalonia.Controls/TreeViewItem.cs
index 3ac157f727..a7ac41c153 100644
--- a/src/Avalonia.Controls/TreeViewItem.cs
+++ b/src/Avalonia.Controls/TreeViewItem.cs
@@ -90,8 +90,20 @@ namespace Avalonia.Controls
 
         internal TreeView? TreeViewOwner => _treeView;
 
-        protected internal override Control CreateContainerForItemOverride() => new TreeViewItem();
-        protected internal override bool IsItemItsOwnContainerOverride(Control item) => item is TreeViewItem;
+        protected internal override Control CreateContainerForItemOverride()
+        {
+            return EnsureTreeView().CreateContainerForItemOverride();
+        }
+
+        protected internal override bool IsItemItsOwnContainerOverride(Control item)
+        {
+            return EnsureTreeView().IsItemItsOwnContainerOverride(item);
+        }
+
+        protected internal override void PrepareContainerForItemOverride(Control container, object? item, int index)
+        {
+            EnsureTreeView().PrepareContainerForItemOverride(container, item, index);
+        }
 
         /// <inheritdoc/>
         protected override void OnAttachedToLogicalTree(LogicalTreeAttachmentEventArgs e)
@@ -283,6 +295,9 @@ namespace Avalonia.Controls
             return logical != null ? result : @default;
         }
 
+        private TreeView EnsureTreeView() => _treeView ??
+            throw new InvalidOperationException("The TreeViewItem is not part of a TreeView.");
+
         private void HeaderDoubleTapped(object? sender, TappedEventArgs e)
         {
             OnHeaderDoubleTapped(e);

From a00946492d104c36ba148f1f17048089d6aa2423 Mon Sep 17 00:00:00 2001
From: Benedikt Stebner <Gillibald@users.noreply.github.com>
Date: Fri, 24 Mar 2023 19:04:21 +0100
Subject: [PATCH 25/40] Fix failing test

---
 .../Media/TextFormatting/TextLineImpl.cs      | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/Avalonia.Base/Media/TextFormatting/TextLineImpl.cs b/src/Avalonia.Base/Media/TextFormatting/TextLineImpl.cs
index f522ffb5c3..f5812f71ff 100644
--- a/src/Avalonia.Base/Media/TextFormatting/TextLineImpl.cs
+++ b/src/Avalonia.Base/Media/TextFormatting/TextLineImpl.cs
@@ -697,6 +697,16 @@ namespace Avalonia.Media.TextFormatting
 
                     i = lastRunIndex;
 
+                    //Possible overlap at runs of different direction
+                    if (directionalWidth == 0)
+                    {
+                        //In case a run only contains a linebreak we don't want to skip it.
+                        if (currentRun is ShapedTextRun shaped && currentRun.Length - shaped.GlyphRun.Metrics.NewLineLength > 0)
+                        {
+                            continue;
+                        }
+                    }
+
                     int coveredLength;
                     TextBounds? textBounds;
 
@@ -826,6 +836,16 @@ namespace Avalonia.Media.TextFormatting
 
                     i = firstRunIndex;
 
+                    //Possible overlap at runs of different direction
+                    if (directionalWidth == 0)
+                    {
+                        //In case a run only contains a linebreak we don't want to skip it.
+                        if (currentRun is ShapedTextRun shaped && currentRun.Length - shaped.GlyphRun.Metrics.NewLineLength > 0)
+                        {
+                            continue;
+                        }
+                    }
+
                     TextBounds? textBounds = null;
                     int coveredLength;
 

From c2b47db2b1ce6260eef0dd75373c9c14d7b8b4d0 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Fri, 24 Mar 2023 23:43:49 +0100
Subject: [PATCH 26/40] Added failing test for #10769.

And adjust terminology in tests.
---
 .../VirtualizingStackPanelTests.cs            | 42 +++++++++++++++++--
 1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/tests/Avalonia.Controls.UnitTests/VirtualizingStackPanelTests.cs b/tests/Avalonia.Controls.UnitTests/VirtualizingStackPanelTests.cs
index 42b419bbcc..7f5c0eb134 100644
--- a/tests/Avalonia.Controls.UnitTests/VirtualizingStackPanelTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/VirtualizingStackPanelTests.cs
@@ -92,7 +92,40 @@ namespace Avalonia.Controls.UnitTests
         }
 
         [Fact]
-        public void Creates_Elements_On_Item_Insert()
+        public void Creates_Elements_On_Item_Insert_1()
+        {
+            using var app = App();
+            var (target, _, itemsControl) = CreateTarget();
+            var items = (IList)itemsControl.ItemsSource!;
+
+            Assert.Equal(10, target.GetRealizedElements().Count);
+
+            items.Insert(0, "new");
+
+            Assert.Equal(11, target.GetRealizedElements().Count);
+
+            var indexes = GetRealizedIndexes(target, itemsControl);
+
+            // Blank space inserted in realized elements and subsequent indexes updated.
+            Assert.Equal(new[] { -1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }, indexes);
+
+            var elements = target.GetRealizedElements().ToList();
+            Layout(target);
+
+            indexes = GetRealizedIndexes(target, itemsControl);
+
+            // After layout an element for the new element is created.
+            Assert.Equal(Enumerable.Range(0, 10), indexes);
+
+            // But apart from the new element and the removed last element, all existing elements
+            // should be the same.
+            elements[0] = target.GetRealizedElements().ElementAt(0);
+            elements.RemoveAt(elements.Count - 1);
+            Assert.Equal(elements, target.GetRealizedElements());
+        }
+
+        [Fact]
+        public void Creates_Elements_On_Item_Insert_2()
         {
             using var app = App();
             var (target, _, itemsControl) = CreateTarget();
@@ -106,7 +139,7 @@ namespace Avalonia.Controls.UnitTests
 
             var indexes = GetRealizedIndexes(target, itemsControl);
 
-            // Blank space inserted in realized elements and subsequent row indexes updated.
+            // Blank space inserted in realized elements and subsequent indexes updated.
             Assert.Equal(new[] { 0, 1, -1, 3, 4, 5, 6, 7, 8, 9, 10 }, indexes);
 
             var elements = target.GetRealizedElements().ToList();
@@ -114,10 +147,11 @@ namespace Avalonia.Controls.UnitTests
 
             indexes = GetRealizedIndexes(target, itemsControl);
 
-            // After layout an element for the new row is created.
+            // After layout an element for the new element is created.
             Assert.Equal(Enumerable.Range(0, 10), indexes);
 
-            // But apart from the new row and the removed last row, all existing elements should be the same.
+            // But apart from the new element and the removed last element, all existing elements
+            // should be the same.
             elements[2] = target.GetRealizedElements().ElementAt(2);
             elements.RemoveAt(elements.Count - 1);
             Assert.Equal(elements, target.GetRealizedElements());

From 58676fb417b518ca205c8e162a8e362c2603c9f4 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Fri, 24 Mar 2023 23:44:36 +0100
Subject: [PATCH 27/40] Fix comparison.

The first element is index 0.
---
 src/Avalonia.Controls/VirtualizingStackPanel.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Avalonia.Controls/VirtualizingStackPanel.cs b/src/Avalonia.Controls/VirtualizingStackPanel.cs
index dfacb93eeb..e86a0de657 100644
--- a/src/Avalonia.Controls/VirtualizingStackPanel.cs
+++ b/src/Avalonia.Controls/VirtualizingStackPanel.cs
@@ -1088,7 +1088,7 @@ namespace Avalonia.Controls
                         ++newIndex;
                     }
 
-                    if (realizedIndex <= 0)
+                    if (realizedIndex < 0)
                     {
                         // The insertion point was before the first element, update the first index.
                         _firstIndex += count;

From b3fe7827a2019c9c51e7c753d8bd5340a3938f0a Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sat, 25 Mar 2023 11:33:29 +0600
Subject: [PATCH 28/40] Fixed Dispatcher.Invoke when called from the UI thread

---
 .../Threading/Dispatcher.Invoke.cs            |  3 +-
 .../Threading/Dispatcher.Queue.cs             |  8 +-
 src/Avalonia.Base/Threading/Dispatcher.cs     |  1 +
 .../Threading/DispatcherOperation.cs          | 65 +++++++++++-
 .../Threading/DispatcherPriority.cs           |  4 +-
 .../DispatcherTests.cs                        | 98 +++++++++++++++++--
 6 files changed, 165 insertions(+), 14 deletions(-)

diff --git a/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs b/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
index 80b62b3818..a75ce36074 100644
--- a/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
+++ b/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
@@ -2,6 +2,7 @@ using System;
 using System.ComponentModel;
 using System.Diagnostics;
 using System.Threading;
+using System.Threading.Tasks;
 
 namespace Avalonia.Threading;
 
@@ -482,7 +483,7 @@ public partial class Dispatcher
             // invoke.
             try
             {
-                operation.GetTask().Wait();
+                operation.Wait();
 
                 Debug.Assert(operation.Status == DispatcherOperationStatus.Completed ||
                              operation.Status == DispatcherOperationStatus.Aborted);
diff --git a/src/Avalonia.Base/Threading/Dispatcher.Queue.cs b/src/Avalonia.Base/Threading/Dispatcher.Queue.cs
index c91af1a514..dffa1f3366 100644
--- a/src/Avalonia.Base/Threading/Dispatcher.Queue.cs
+++ b/src/Avalonia.Base/Threading/Dispatcher.Queue.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Diagnostics;
+using System.Threading;
 
 namespace Avalonia.Threading;
 
@@ -42,11 +43,16 @@ public partial class Dispatcher
     /// Force-runs all dispatcher operations ignoring any pending OS events, use with caution
     /// </summary>
     public void RunJobs(DispatcherPriority? priority = null)
+    {
+        RunJobs(priority, CancellationToken.None);
+    }
+    
+    internal void RunJobs(DispatcherPriority? priority, CancellationToken cancellationToken)
     {
         priority ??= DispatcherPriority.MinimumActiveValue;
         if (priority < DispatcherPriority.MinimumActiveValue)
             priority = DispatcherPriority.MinimumActiveValue;
-        while (true)
+        while (!cancellationToken.IsCancellationRequested)
         {
             DispatcherOperation? job;
             lock (InstanceLock)
diff --git a/src/Avalonia.Base/Threading/Dispatcher.cs b/src/Avalonia.Base/Threading/Dispatcher.cs
index 25a4a4ce2c..457e701331 100644
--- a/src/Avalonia.Base/Threading/Dispatcher.cs
+++ b/src/Avalonia.Base/Threading/Dispatcher.cs
@@ -37,6 +37,7 @@ public partial class Dispatcher : IDispatcher
     }
     
     public static Dispatcher UIThread => s_uiThread ??= CreateUIThreadDispatcher();
+    public bool SupportsRunLoops => _controlledImpl != null;
 
     private static Dispatcher CreateUIThreadDispatcher()
     {
diff --git a/src/Avalonia.Base/Threading/DispatcherOperation.cs b/src/Avalonia.Base/Threading/DispatcherOperation.cs
index 173ab81ef8..844ce272c9 100644
--- a/src/Avalonia.Base/Threading/DispatcherOperation.cs
+++ b/src/Avalonia.Base/Threading/DispatcherOperation.cs
@@ -111,11 +111,68 @@ public class DispatcherOperation
         }
     }
 
-    public void Wait()
+    /// <summary>
+    ///     Waits for this operation to complete.
+    /// </summary>
+    /// <returns>
+    ///     The status of the operation.  To obtain the return value
+    ///     of the invoked delegate, use the the Result property.
+    /// </returns>
+    public void Wait() => Wait(TimeSpan.FromMilliseconds(-1));
+
+    /// <summary>
+    ///     Waits for this operation to complete.
+    /// </summary>
+    /// <param name="timeout">
+    ///     The maximum amount of time to wait.
+    /// </param>
+    public void Wait(TimeSpan timeout)
     {
-        if (Dispatcher.CheckAccess())
-            throw new InvalidOperationException("Wait is only supported on background thread");
-        GetTask().Wait();
+        if ((Status == DispatcherOperationStatus.Pending || Status == DispatcherOperationStatus.Executing) &&
+            timeout.TotalMilliseconds != 0)
+        {
+            if (Dispatcher.CheckAccess())
+            {
+                if (Status == DispatcherOperationStatus.Executing)
+                {
+                    // We are the dispatching thread, and the current operation state is
+                    // executing, which means that the operation is in the middle of
+                    // executing (on this thread) and is trying to wait for the execution
+                    // to complete.  Unfortunately, the thread will now deadlock, so
+                    // we throw an exception instead.
+                    throw new InvalidOperationException("A thread cannot wait on operations already running on the same thread.");
+                }
+                
+                var cts = new CancellationTokenSource();
+                EventHandler finishedHandler = delegate
+                {
+                    cts.Cancel();
+                };
+                Completed += finishedHandler;
+                Aborted += finishedHandler;
+                try
+                {
+                    while (Status == DispatcherOperationStatus.Pending)
+                    {
+                        if (Dispatcher.SupportsRunLoops)
+                        {
+                            if (Priority >= DispatcherPriority.MinimumForegroundPriority)
+                                Dispatcher.RunJobs(Priority, cts.Token);
+                            else
+                                Dispatcher.MainLoop(cts.Token);
+                        }
+                        else
+                            Dispatcher.RunJobs(DispatcherPriority.MinimumActiveValue, cts.Token);
+                    }
+                }
+                finally
+                {
+                    Completed -= finishedHandler;
+                    Aborted -= finishedHandler;
+                }
+            }
+        }
+        GetTask().GetAwaiter().GetResult();
     }
 
     public Task GetTask() => GetTaskCore();
diff --git a/src/Avalonia.Base/Threading/DispatcherPriority.cs b/src/Avalonia.Base/Threading/DispatcherPriority.cs
index a71140d288..3017b45dc7 100644
--- a/src/Avalonia.Base/Threading/DispatcherPriority.cs
+++ b/src/Avalonia.Base/Threading/DispatcherPriority.cs
@@ -20,7 +20,9 @@ namespace Avalonia.Threading
         /// <summary>
         /// The lowest foreground dispatcher priority
         /// </summary>
-        internal static readonly DispatcherPriority Default = new(0);
+        public static readonly DispatcherPriority Default = new(0);
+
+        internal static readonly DispatcherPriority MinimumForegroundPriority = Default;
         
         /// <summary>
         /// The job will be processed with the same priority as input.
diff --git a/tests/Avalonia.Base.UnitTests/DispatcherTests.cs b/tests/Avalonia.Base.UnitTests/DispatcherTests.cs
index 38175ad410..e429544172 100644
--- a/tests/Avalonia.Base.UnitTests/DispatcherTests.cs
+++ b/tests/Avalonia.Base.UnitTests/DispatcherTests.cs
@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
+using System.Threading;
 using Avalonia.Threading;
 using Xunit;
 namespace Avalonia.Base.UnitTests;
@@ -9,9 +11,14 @@ public class DispatcherTests
 {
     class SimpleDispatcherImpl : IDispatcherImpl, IDispatcherImplWithPendingInput
     {
-        public bool CurrentThreadIsLoopThread => true;
-
-        public void Signal() => AskedForSignal = true;
+        private Thread _loopThread = Thread.CurrentThread;
+        private object _lock = new();
+        public bool CurrentThreadIsLoopThread => Thread.CurrentThread == _loopThread;
+        public void Signal()
+        {
+            lock (_lock)
+                AskedForSignal = true;
+        }
 
         public event Action Signaled;
         public event Action Timer;
@@ -27,9 +34,12 @@ public class DispatcherTests
 
         public void ExecuteSignal()
         {
-            if (!AskedForSignal)
-                return;
-            AskedForSignal = false;
+            lock (_lock)
+            {
+                if (!AskedForSignal)
+                    return;
+                AskedForSignal = false;
+            }
             Signaled?.Invoke();
         }
 
@@ -45,6 +55,61 @@ public class DispatcherTests
         public bool HasPendingInput => TestInputPending == true;
         public bool? TestInputPending { get; set; }
     }
+
+    class SimpleDispatcherWithBackgroundProcessingImpl : SimpleDispatcherImpl, IDispatcherImplWithExplicitBackgroundProcessing
+    {
+        public bool AskedForBackgroundProcessing { get; private set; }
+        public event Action ReadyForBackgroundProcessing;
+        public void RequestBackgroundProcessing()
+        {
+            if (!CurrentThreadIsLoopThread)
+                throw new InvalidOperationException();
+            AskedForBackgroundProcessing = true;
+        }
+
+        public void FireBackgroundProcessing()
+        {
+            if(!AskedForBackgroundProcessing)
+                return;
+            AskedForBackgroundProcessing = false;
+            ReadyForBackgroundProcessing?.Invoke();
+        }
+    }
+    
+    class SimpleControlledDispatcherImpl : SimpleDispatcherWithBackgroundProcessingImpl, IControlledDispatcherImpl
+    {
+        private readonly bool _useTestTimeout = true;
+        private readonly CancellationToken? _cancel;
+        public int RunLoopCount { get; private set; }
+        
+        public SimpleControlledDispatcherImpl()
+        {
+            
+        }
+
+        public SimpleControlledDispatcherImpl(CancellationToken cancel, bool useTestTimeout = false)
+        {
+            _useTestTimeout = useTestTimeout;
+            _cancel = cancel;
+        }
+        
+        public void RunLoop(CancellationToken token)
+        {
+            RunLoopCount++;
+            var st = Stopwatch.StartNew();
+            while (!token.IsCancellationRequested || _cancel?.IsCancellationRequested == true)
+            {
+                FireBackgroundProcessing();
+                ExecuteSignal();
+                if (_useTestTimeout)
+                    Assert.True(st.ElapsedMilliseconds < 4000, "RunLoop exceeded test time quota");
+                else
+                    Thread.Sleep(10);
+            }
+        }
+
+
+    }
     
     
     [Fact]
@@ -169,5 +234,24 @@ public class DispatcherTests
             impl.TestInputPending = false;
         }
     }
-    
+
+    [Theory,
+     InlineData(false, false),
+     InlineData(false, true),
+     InlineData(true, false),
+     InlineData(true, true)]
+    public void CanWaitForDispatcherOperationFromTheSameThread(bool controlled, bool foreground)
+    {
+        var impl = controlled ? new SimpleControlledDispatcherImpl() : new SimpleDispatcherImpl();
+        var disp = new Dispatcher(impl);
+        bool finished = false;
+
+        disp.InvokeAsync(() => finished = true,
+            foreground ? DispatcherPriority.Default : DispatcherPriority.Background).Wait();
+
+        Assert.True(finished);
+        if (controlled) 
+            Assert.Equal(foreground ? 0 : 1, ((SimpleControlledDispatcherImpl)impl).RunLoopCount);
+    }
+
 }
\ No newline at end of file

From d71a54ed58841997b88de163ca9abf38d9cbc19c Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sat, 25 Mar 2023 11:33:53 +0600
Subject: [PATCH 29/40] Added Dispatcher.InvokeTaskAsync helpers

---
 .../Threading/Dispatcher.Invoke.cs            | 50 +++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs b/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
index a75ce36074..568299afca 100644
--- a/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
+++ b/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
@@ -540,6 +540,56 @@ public partial class Dispatcher
         InvokeAsyncImpl(new DispatcherOperation(this, priority, action, true), CancellationToken.None);
     }
 
+    /// <summary>
+    ///     Executes the specified Func<Task> asynchronously on the
+    ///     thread that the Dispatcher was created on
+    /// </summary>
+    /// <param name="callback">
+    ///     A Func<Task> delegate to invoke through the dispatcher.
+    /// </param>
+    /// <param name="priority">
+    ///     The priority that determines in what order the specified
+    ///     callback is invoked relative to the other pending operations
+    ///     in the Dispatcher.
+    /// </param>
+    /// <returns>
+    ///     An task that completes after the task returned from callback finishes
+    /// </returns>
+    /// <remarks>
+    /// DispatcherPriority is only respected for the initial call, any async continuations will be executed through
+    /// SynchronizationContext
+    /// </remarks>
+    public Task InvokeTaskAsync(Func<Task> callback, DispatcherPriority priority = default)
+    {
+        _ = callback ?? throw new ArgumentNullException(nameof(callback));
+        return InvokeAsync(callback, priority).GetTask().Unwrap();
+    }
+    
+    /// <summary>
+    ///     Executes the specified Func<Task<TResult>> asynchronously on the
+    ///     thread that the Dispatcher was created on
+    /// </summary>
+    /// <param name="callback">
+    ///     A Func<Task<TResult>> delegate to invoke through the dispatcher.
+    /// </param>
+    /// <param name="priority">
+    ///     The priority that determines in what order the specified
+    ///     callback is invoked relative to the other pending operations
+    ///     in the Dispatcher.
+    /// </param>
+    /// <returns>
+    ///     An task that completes after the task returned from callback finishes
+    /// </returns>
+    /// <remarks>
+    /// DispatcherPriority is only respected for the initial call, any async continuations will be executed through
+    /// SynchronizationContext
+    /// </remarks>
+    public Task<TResult> InvokeTaskAsync<TResult>(Func<Task<TResult>> action, DispatcherPriority priority = default)
+    {
+        _ = action ?? throw new ArgumentNullException(nameof(action));
+        return InvokeAsync(action, priority).GetTask().Unwrap();
+    }
+
     /// <summary>
     /// Posts an action that will be invoked on the dispatcher thread.
     /// </summary>

From 5f52122bba4487ba948b070342979fda0a2d1f2f Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sat, 25 Mar 2023 15:58:01 +0600
Subject: [PATCH 30/40] Implemented ExitAllFrames, DisableProcessing and
 Shutdown, dispatcher callbacks now have proper sync context

---
 .../AvaloniaSynchronizationContext.cs         |  70 +++++-
 .../Threading/Dispatcher.Invoke.cs            |  14 +-
 .../Threading/Dispatcher.MainLoop.cs          | 210 ++++++++++++++++++
 .../Threading/Dispatcher.Queue.cs             |   6 +-
 src/Avalonia.Base/Threading/Dispatcher.cs     |  50 +----
 .../Threading/DispatcherFrame.cs              | 125 +++++++++++
 .../Threading/DispatcherOperation.cs          |  57 ++++-
 .../Threading}/NonPumpingSyncContext.cs       |  24 +-
 .../Utilities/NonPumpingLockHelper.cs         |  11 +-
 .../Avalonia.Win32/Avalonia.Win32.csproj      |   4 +-
 .../NonPumpingWaitHelperImpl.cs               |  13 ++
 src/Windows/Avalonia.Win32/Win32Platform.cs   |   2 +-
 .../Avalonia.Win32/WindowImpl.AppWndProc.cs   |   4 +-
 .../DispatcherTests.cs                        | 204 +++++++++++++++++
 14 files changed, 715 insertions(+), 79 deletions(-)
 create mode 100644 src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs
 create mode 100644 src/Avalonia.Base/Threading/DispatcherFrame.cs
 rename src/{Windows/Avalonia.Win32 => Avalonia.Base/Threading}/NonPumpingSyncContext.cs (72%)
 create mode 100644 src/Windows/Avalonia.Win32/NonPumpingWaitHelperImpl.cs

diff --git a/src/Avalonia.Base/Threading/AvaloniaSynchronizationContext.cs b/src/Avalonia.Base/Threading/AvaloniaSynchronizationContext.cs
index 1b29cf32f7..e0563876bf 100644
--- a/src/Avalonia.Base/Threading/AvaloniaSynchronizationContext.cs
+++ b/src/Avalonia.Base/Threading/AvaloniaSynchronizationContext.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Runtime.ConstrainedExecution;
 using System.Threading;
+using Avalonia.Utilities;
 
 namespace Avalonia.Threading
 {
@@ -9,6 +10,28 @@ namespace Avalonia.Threading
     /// </summary>
     public class AvaloniaSynchronizationContext : SynchronizationContext
     {
+        internal readonly DispatcherPriority Priority;
+        private readonly NonPumpingLockHelper.IHelperImpl? _nonPumpingHelper =
+            AvaloniaLocator.Current.GetService<NonPumpingLockHelper.IHelperImpl>();
+        
+        public AvaloniaSynchronizationContext():  this(Thread.CurrentThread.GetApartmentState() == ApartmentState.STA)
+        {
+            
+        }
+        
+        // This constructor is here to enforce STA behavior for unit tests
+        internal AvaloniaSynchronizationContext(bool isStaThread)
+        {
+            if (_nonPumpingHelper != null 
+                && isStaThread)
+                SetWaitNotificationRequired();
+        }
+
+        public AvaloniaSynchronizationContext(DispatcherPriority priority)
+        {
+            Priority = priority;
+        }
+        
         /// <summary>
         /// Controls if SynchronizationContext should be installed in InstallIfNeeded. Used by Designer.
         /// </summary>
@@ -24,13 +47,13 @@ namespace Avalonia.Threading
                 return;
             }
 
-            SetSynchronizationContext(new AvaloniaSynchronizationContext());
+            SetSynchronizationContext(Dispatcher.UIThread.GetContextWithPriority(DispatcherPriority.Normal));
         }
 
         /// <inheritdoc/>
         public override void Post(SendOrPostCallback d, object? state)
         {
-            Dispatcher.UIThread.Post(d, state, DispatcherPriority.Background);
+            Dispatcher.UIThread.Post(d, state, Priority);
         }
 
         /// <inheritdoc/>
@@ -41,7 +64,50 @@ namespace Avalonia.Threading
             else
                 Dispatcher.UIThread.InvokeAsync(() => d(state), DispatcherPriority.Send).GetAwaiter().GetResult();
         }
+        
+#if !NET6_0_OR_GREATER
+        [PrePrepareMethod]
+#endif
+        public override int Wait(IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout)
+        {
+            if (
+                _nonPumpingHelper != null
+                && Dispatcher.UIThread.CheckAccess() 
+                && Dispatcher.UIThread.DisabledProcessingCount > 0)
+                return _nonPumpingHelper.Wait(waitHandles, waitAll, millisecondsTimeout);
+            return base.Wait(waitHandles, waitAll, millisecondsTimeout);
+        }
 
+        public record struct RestoreContext : IDisposable
+        {
+            private readonly SynchronizationContext? _oldContext;
+            private bool _needRestore;
 
+            internal RestoreContext(SynchronizationContext? oldContext)
+            {
+                _oldContext = oldContext;
+                _needRestore = true;
+            }
+            
+            public void Dispose()
+            {
+                if (_needRestore)
+                {
+                    SetSynchronizationContext(_oldContext);
+                    _needRestore = false;
+                }
+            }
+        }
+
+        public static RestoreContext Ensure(DispatcherPriority priority)
+        {
+            if (Current is AvaloniaSynchronizationContext avaloniaContext 
+                && avaloniaContext.Priority == priority)
+                return default;
+            var oldContext = Current;
+            Dispatcher.UIThread.VerifyAccess();
+            SetSynchronizationContext(Dispatcher.UIThread.GetContextWithPriority(priority));
+            return new RestoreContext(oldContext);
+        }
     }
 }
diff --git a/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs b/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
index 568299afca..68f9cc7e2e 100644
--- a/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
+++ b/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
@@ -107,7 +107,8 @@ public partial class Dispatcher
         // call the callback directly.
         if (!cancellationToken.IsCancellationRequested && priority == DispatcherPriority.Send && CheckAccess())
         {
-            callback();
+            using (AvaloniaSynchronizationContext.Ensure(priority))
+                callback();
             return;
         }
 
@@ -228,7 +229,8 @@ public partial class Dispatcher
         // call the callback directly.
         if (!cancellationToken.IsCancellationRequested && priority == DispatcherPriority.Send && CheckAccess())
         {
-            return callback();
+            using (AvaloniaSynchronizationContext.Ensure(priority))
+                return callback();
         }
 
         // Slow-Path: go through the queue.
@@ -555,10 +557,6 @@ public partial class Dispatcher
     /// <returns>
     ///     An task that completes after the task returned from callback finishes
     /// </returns>
-    /// <remarks>
-    /// DispatcherPriority is only respected for the initial call, any async continuations will be executed through
-    /// SynchronizationContext
-    /// </remarks>
     public Task InvokeTaskAsync(Func<Task> callback, DispatcherPriority priority = default)
     {
         _ = callback ?? throw new ArgumentNullException(nameof(callback));
@@ -580,10 +578,6 @@ public partial class Dispatcher
     /// <returns>
     ///     An task that completes after the task returned from callback finishes
     /// </returns>
-    /// <remarks>
-    /// DispatcherPriority is only respected for the initial call, any async continuations will be executed through
-    /// SynchronizationContext
-    /// </remarks>
     public Task<TResult> InvokeTaskAsync<TResult>(Func<Task<TResult>> action, DispatcherPriority priority = default)
     {
         _ = action ?? throw new ArgumentNullException(nameof(action));
diff --git a/src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs b/src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs
new file mode 100644
index 0000000000..cabbabcf6b
--- /dev/null
+++ b/src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs
@@ -0,0 +1,210 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using Avalonia.Utilities;
+
+namespace Avalonia.Threading;
+
+public partial class Dispatcher
+{
+    internal bool ExitAllFramesRequested { get; private set; }
+    internal bool HasShutdownStarted { get; private set; }
+    internal int DisabledProcessingCount { get; private set; }
+    private bool _hasShutdownFinished;
+    private bool _startingShutdown;
+    
+    private Stack<DispatcherFrame> _frames = new();
+    
+
+    /// <summary>
+    ///     Raised when the dispatcher is shutting down.
+    /// </summary>
+    public event EventHandler? ShutdownStarted;
+
+    /// <summary>
+    ///     Raised when the dispatcher is shut down.
+    /// </summary>
+    public event EventHandler? ShutdownFinished;
+
+    /// <summary>
+    ///     Push an execution frame.
+    /// </summary>
+    /// <param name="frame">
+    ///     The frame for the dispatcher to process.
+    /// </param>
+    public void PushFrame(DispatcherFrame frame)
+    {
+        VerifyAccess();
+        if (_controlledImpl == null)
+            throw new PlatformNotSupportedException();
+        _ = frame ?? throw new ArgumentNullException(nameof(frame));
+
+        if(_hasShutdownFinished) // Dispatcher thread - no lock needed for read
+            throw new InvalidOperationException("Cannot perform requested operation because the Dispatcher shut down");
+
+        if (DisabledProcessingCount > 0)
+            throw new InvalidOperationException(
+                "Cannot perform this operation while dispatcher processing is suspended.");
+
+        try
+        {
+            _frames.Push(frame);
+            using (AvaloniaSynchronizationContext.Ensure(DispatcherPriority.Normal))
+                frame.Run(_controlledImpl);
+        }
+        finally
+        {
+            _frames.Pop();
+            if (_frames.Count == 0)
+            {
+                if (HasShutdownStarted)
+                    ShutdownImpl();
+                else
+                    ExitAllFramesRequested = false;
+            }
+        }
+    }
+    
+    /// <summary>
+    /// Runs the dispatcher's main loop.
+    /// </summary>
+    /// <param name="cancellationToken">
+    /// A cancellation token used to exit the main loop.
+    /// </param>
+    public void MainLoop(CancellationToken cancellationToken)
+    {
+        if (_controlledImpl == null)
+            throw new PlatformNotSupportedException();
+        var frame = new DispatcherFrame();
+        cancellationToken.Register(() => frame.Continue = false);
+        PushFrame(frame);
+    }
+    
+    /// <summary>
+    ///     Requests that all nested frames exit.
+    /// </summary>
+    public void ExitAllFrames()
+    {
+        if (_frames.Count == 0)
+            return;
+        ExitAllFramesRequested = true;
+        foreach (var f in _frames)
+            f.MaybeExitOnDispatcherRequest();
+    }
+    
+    /// <summary>
+    ///     Begins the process of shutting down the dispatcher.
+    /// </summary>
+    public void BeginInvokeShutdown(DispatcherPriority priority) => Post(StartShutdownImpl, priority);
+
+    private void StartShutdownImpl()
+    {
+        if (!_startingShutdown)
+        {
+            // We only need this to prevent reentrancy if the ShutdownStarted event
+            // tries to shut down again.
+            _startingShutdown = true;
+
+            // Call the ShutdownStarted event before we actually mark ourselves
+            // as shutting down.  This is so the handlers can actually do work
+            // when they get this event without throwing exceptions.
+            ShutdownStarted?.Invoke(this, EventArgs.Empty);
+
+            HasShutdownStarted = true;
+            
+            if (_frames.Count > 0)
+                ExitAllFrames();
+            else ShutdownImpl();
+        }
+    }
+
+
+    private void ShutdownImpl()
+    {
+        DispatcherOperation? operation = null;
+        _impl.Timer -= PromoteTimers;
+        _impl.Signaled -= Signaled;
+        do
+        {
+            lock (InstanceLock)
+            {
+                if (_queue.MaxPriority != DispatcherPriority.Invalid)
+                {
+                    operation = _queue.Peek();
+                }
+                else
+                {
+                    operation = null;
+                }
+            }
+
+            if (operation != null)
+            {
+                operation.Abort();
+            }
+        } while (operation != null);
+
+        _impl.UpdateTimer(null);
+        _hasShutdownFinished = true;
+        ShutdownFinished?.Invoke(this, EventArgs.Empty);
+    }
+
+    public record struct DispatcherProcessingDisabled : IDisposable
+    {
+        private readonly SynchronizationContext? _oldContext;
+        
+        private readonly bool _restoreContext;
+        private Dispatcher? _dispatcher;
+
+        internal DispatcherProcessingDisabled(Dispatcher dispatcher)
+        {
+            _dispatcher = dispatcher;
+        }
+
+        internal DispatcherProcessingDisabled(Dispatcher dispatcher, SynchronizationContext? oldContext) : this(
+            dispatcher)
+        {
+            _oldContext = oldContext;
+            _restoreContext = true;
+        }
+        
+        public void Dispose()
+        {
+            if(_dispatcher==null)
+                return;
+            _dispatcher.DisabledProcessingCount--;
+            _dispatcher = null;
+            if (_restoreContext)
+                SynchronizationContext.SetSynchronizationContext(_oldContext);
+        }
+    }
+    
+    /// <summary>
+    ///     Disable the event processing of the dispatcher.
+    /// </summary>
+    /// <remarks>
+    ///     This is an advanced method intended to eliminate the chance of
+    ///     unrelated reentrancy.  The effect of disabling processing is:
+    ///     1) CLR locks will not pump messages internally.
+    ///     2) No one is allowed to push a frame.
+    ///     3) No message processing is permitted.
+    /// </remarks>
+    public DispatcherProcessingDisabled DisableProcessing()
+    {
+        VerifyAccess();
+
+        // Turn off processing.
+        DisabledProcessingCount++;
+        var oldContext = SynchronizationContext.Current;
+        if (oldContext is AvaloniaSynchronizationContext or NonPumpingSyncContext)
+            return new DispatcherProcessingDisabled(this);
+
+        var helper = AvaloniaLocator.Current.GetService<NonPumpingLockHelper.IHelperImpl>();
+        if (helper == null)
+            return new DispatcherProcessingDisabled(this);
+
+        SynchronizationContext.SetSynchronizationContext(new NonPumpingSyncContext(helper, oldContext));
+        return new DispatcherProcessingDisabled(this, oldContext);
+
+    }
+}
\ No newline at end of file
diff --git a/src/Avalonia.Base/Threading/Dispatcher.Queue.cs b/src/Avalonia.Base/Threading/Dispatcher.Queue.cs
index dffa1f3366..78a0740e56 100644
--- a/src/Avalonia.Base/Threading/Dispatcher.Queue.cs
+++ b/src/Avalonia.Base/Threading/Dispatcher.Queue.cs
@@ -49,6 +49,10 @@ public partial class Dispatcher
     
     internal void RunJobs(DispatcherPriority? priority, CancellationToken cancellationToken)
     {
+        if (DisabledProcessingCount > 0)
+            throw new InvalidOperationException(
+                "Cannot perform this operation while dispatcher processing is suspended.");
+        
         priority ??= DispatcherPriority.MinimumActiveValue;
         if (priority < DispatcherPriority.MinimumActiveValue)
             priority = DispatcherPriority.MinimumActiveValue;
@@ -174,7 +178,7 @@ public partial class Dispatcher
         }
     }
 
-    private bool RequestProcessing()
+    internal bool RequestProcessing()
     {
         lock (InstanceLock)
         {
diff --git a/src/Avalonia.Base/Threading/Dispatcher.cs b/src/Avalonia.Base/Threading/Dispatcher.cs
index 457e701331..f257072dc8 100644
--- a/src/Avalonia.Base/Threading/Dispatcher.cs
+++ b/src/Avalonia.Base/Threading/Dispatcher.cs
@@ -18,11 +18,13 @@ public partial class Dispatcher : IDispatcher
 {
     private IDispatcherImpl _impl;
     internal object InstanceLock { get; } = new();
-    private bool _hasShutdownFinished;
     private IControlledDispatcherImpl? _controlledImpl;
     private static Dispatcher? s_uiThread;
     private IDispatcherImplWithPendingInput? _pendingInputImpl;
-    private IDispatcherImplWithExplicitBackgroundProcessing? _backgroundProcessingImpl;
+    private readonly IDispatcherImplWithExplicitBackgroundProcessing? _backgroundProcessingImpl;
+
+    private readonly AvaloniaSynchronizationContext?[] _priorityContexts =
+        new AvaloniaSynchronizationContext?[DispatcherPriority.MaxValue - DispatcherPriority.MinValue + 1];
 
     internal Dispatcher(IDispatcherImpl impl)
     {
@@ -73,50 +75,14 @@ public partial class Dispatcher : IDispatcher
             [MethodImpl(MethodImplOptions.NoInlining)]
             static void ThrowVerifyAccess()
                 => throw new InvalidOperationException("Call from invalid thread");
-
             ThrowVerifyAccess();
         }
     }
 
-    internal void Shutdown()
-    {
-        DispatcherOperation? operation = null;
-        _impl.Timer -= PromoteTimers;
-        _impl.Signaled -= Signaled;
-        do
-        {
-            lock(InstanceLock)
-            {
-                if(_queue.MaxPriority != DispatcherPriority.Invalid)
-                {
-                    operation = _queue.Peek();
-                }
-                else
-                {
-                    operation = null;
-                }
-            }
-
-            if(operation != null)
-            {
-                operation.Abort();
-            }
-        } while(operation != null);
-        _impl.UpdateTimer(null);
-        _hasShutdownFinished = true;
-    }
-
-    /// <summary>
-    /// Runs the dispatcher's main loop.
-    /// </summary>
-    /// <param name="cancellationToken">
-    /// A cancellation token used to exit the main loop.
-    /// </param>
-    public void MainLoop(CancellationToken cancellationToken)
+    internal AvaloniaSynchronizationContext GetContextWithPriority(DispatcherPriority priority)
     {
-        if (_controlledImpl == null)
-            throw new PlatformNotSupportedException();
-        cancellationToken.Register(() => RequestProcessing());
-        _controlledImpl.RunLoop(cancellationToken);
+        DispatcherPriority.Validate(priority, nameof(priority));
+        var index = priority - DispatcherPriority.MinValue;
+        return _priorityContexts[index] ??= new(priority);
     }
 }
diff --git a/src/Avalonia.Base/Threading/DispatcherFrame.cs b/src/Avalonia.Base/Threading/DispatcherFrame.cs
new file mode 100644
index 0000000000..1f8974dfa3
--- /dev/null
+++ b/src/Avalonia.Base/Threading/DispatcherFrame.cs
@@ -0,0 +1,125 @@
+using System;
+using System.Threading;
+
+namespace Avalonia.Threading;
+
+/// <summary>
+///     Representation of Dispatcher frame.
+/// </summary>
+public class DispatcherFrame
+{
+    private bool _exitWhenRequested;
+    private bool _continue;
+    private bool _isRunning;
+    private CancellationTokenSource? _cancellationTokenSource;
+    
+    /// <summary>
+    ///     Constructs a new instance of the DispatcherFrame class.
+    /// </summary>
+    public DispatcherFrame() : this(true)
+    {
+    }
+
+    public Dispatcher Dispatcher { get; }
+    
+    /// <summary>
+    ///     Constructs a new instance of the DispatcherFrame class.
+    /// </summary>
+    /// <param name="exitWhenRequested">
+    ///     Indicates whether or not this frame will exit when all frames
+    ///     are requested to exit.
+    ///     <p/>
+    ///     Dispatcher frames typically break down into two categories:
+    ///     1) Long running, general purpose frames, that exit only when
+    ///        told to.  These frames should exit when requested.
+    ///     2) Short running, very specific frames that exit themselves
+    ///        when an important criteria is met.  These frames may
+    ///        consider not exiting when requested in favor of waiting
+    ///        for their important criteria to be met.  These frames
+    ///        should have a timeout associated with them.
+    /// </param>
+    public DispatcherFrame(bool exitWhenRequested)
+    {
+        Dispatcher = Dispatcher.UIThread;
+        Dispatcher.VerifyAccess();
+        _exitWhenRequested = exitWhenRequested;
+        _continue = true;
+    }
+
+    /// <summary>
+    ///     Indicates that this dispatcher frame should exit.
+    /// </summary>
+    public bool Continue
+    {
+        get
+        {
+            // This method is free-threaded.
+
+            // First check if this frame wants to continue.
+            bool shouldContinue = _continue;
+            if (shouldContinue)
+            {
+                // This frame wants to continue, so next check if it will
+                // respect the "exit requests" from the dispatcher.
+                if (_exitWhenRequested)
+                {
+                    Dispatcher dispatcher = Dispatcher;
+
+                    // This frame is willing to respect the "exit requests" of
+                    // the dispatcher, so check them.
+                    if (dispatcher.ExitAllFramesRequested || dispatcher.HasShutdownStarted)
+                    {
+                        shouldContinue = false;
+                    }
+                }
+            }
+
+            return shouldContinue;
+        }
+
+        set
+        {
+            // This method is free-threaded.
+            lock (Dispatcher.InstanceLock)
+            {
+                _continue = value;
+                if (!_continue)
+                    _cancellationTokenSource?.Cancel();
+            }
+        }
+    }
+
+    internal void Run(IControlledDispatcherImpl impl)
+    {
+        // Since the actual platform run loop is controlled by a Cancellation token, we are restarting 
+        // it if frame still needs to run
+        while (Continue)
+            RunCore(impl);
+    }
+
+    private void RunCore(IControlledDispatcherImpl impl)
+    {
+        if (_isRunning)
+            throw new InvalidOperationException("This frame is already running");
+        _isRunning = true;
+        try
+        {
+            _cancellationTokenSource = new CancellationTokenSource();
+            // Wake up the dispatcher in case it has pending jobs
+            Dispatcher.RequestProcessing();
+            impl.RunLoop(_cancellationTokenSource.Token);
+        }
+        finally
+        {
+            _isRunning = false;
+            _cancellationTokenSource?.Cancel();
+            _cancellationTokenSource = null;
+        }
+    }
+
+    internal void MaybeExitOnDispatcherRequest()
+    {
+        if (_exitWhenRequested)
+            _cancellationTokenSource?.Cancel();
+    }
+}
\ No newline at end of file
diff --git a/src/Avalonia.Base/Threading/DispatcherOperation.cs b/src/Avalonia.Base/Threading/DispatcherOperation.cs
index 844ce272c9..01652fb731 100644
--- a/src/Avalonia.Base/Threading/DispatcherOperation.cs
+++ b/src/Avalonia.Base/Threading/DispatcherOperation.cs
@@ -159,7 +159,7 @@ public class DispatcherOperation
                             if (Priority >= DispatcherPriority.MinimumForegroundPriority)
                                 Dispatcher.RunJobs(Priority, cts.Token);
                             else
-                                Dispatcher.MainLoop(cts.Token);
+                                Dispatcher.PushFrame(new DispatcherOperationFrame(this, timeout));
                         }
                         else
                             Dispatcher.RunJobs(DispatcherPriority.MinimumActiveValue, cts.Token);
@@ -175,6 +175,58 @@ public class DispatcherOperation
         GetTask().GetAwaiter().GetResult();
     }
 
+    private class DispatcherOperationFrame : DispatcherFrame
+    {
+        // Note: we pass "exitWhenRequested=false" to the base
+        // DispatcherFrame construsctor because we do not want to exit
+        // this frame if the dispatcher is shutting down. This is
+        // because we may need to invoke operations during the shutdown process.
+        public DispatcherOperationFrame(DispatcherOperation op, TimeSpan timeout) : base(false)
+        {
+            _operation = op;
+
+            // We will exit this frame once the operation is completed or aborted.
+            _operation.Aborted += OnCompletedOrAborted;
+            _operation.Completed += OnCompletedOrAborted;
+
+            // We will exit the frame if the operation is not completed within
+            // the requested timeout.
+            if (timeout.TotalMilliseconds > 0)
+            {
+                _waitTimer = new Timer(_ => Exit(),
+                    null,
+                    timeout,
+                    TimeSpan.FromMilliseconds(-1));
+            }
+
+            // Some other thread could have aborted the operation while we were
+            // setting up the handlers.  We check the state again and mark the
+            // frame as "should not continue" if this happened.
+            if (_operation.Status != DispatcherOperationStatus.Pending)
+            {
+                Exit();
+            }
+        }
+
+        private void Exit()
+        {
+            Continue = false;
+
+            if (_waitTimer != null)
+            {
+                _waitTimer.Dispose();
+            }
+
+            _operation.Aborted -= OnCompletedOrAborted;
+            _operation.Completed -= OnCompletedOrAborted;
+        }
+
+        private void OnCompletedOrAborted(object? sender, EventArgs e) => Exit();
+
+        private DispatcherOperation _operation;
+        private Timer? _waitTimer;
+    }
+
     public Task GetTask() => GetTaskCore();
     
     /// <summary>
@@ -205,7 +257,8 @@ public class DispatcherOperation
 
         try
         {
-            InvokeCore();
+            using (AvaloniaSynchronizationContext.Ensure(Priority))
+                InvokeCore();
         }
         finally
         {
diff --git a/src/Windows/Avalonia.Win32/NonPumpingSyncContext.cs b/src/Avalonia.Base/Threading/NonPumpingSyncContext.cs
similarity index 72%
rename from src/Windows/Avalonia.Win32/NonPumpingSyncContext.cs
rename to src/Avalonia.Base/Threading/NonPumpingSyncContext.cs
index 2c4d2c9468..03fc0cc76c 100644
--- a/src/Windows/Avalonia.Win32/NonPumpingSyncContext.cs
+++ b/src/Avalonia.Base/Threading/NonPumpingSyncContext.cs
@@ -2,16 +2,17 @@ using System;
 using System.Runtime.ConstrainedExecution;
 using System.Threading;
 using Avalonia.Utilities;
-using Avalonia.Win32.Interop;
 
-namespace Avalonia.Win32
+namespace Avalonia.Threading
 {
     internal class NonPumpingSyncContext : SynchronizationContext, IDisposable
     {
+        private readonly NonPumpingLockHelper.IHelperImpl _impl;
         private readonly SynchronizationContext? _inner;
 
-        private NonPumpingSyncContext(SynchronizationContext? inner)
+        public NonPumpingSyncContext(NonPumpingLockHelper.IHelperImpl impl, SynchronizationContext? inner)
         {
+            _impl = impl;
             _inner = inner;
             SetWaitNotificationRequired();
             SetSynchronizationContext(this);
@@ -48,15 +49,12 @@ namespace Avalonia.Win32
 #if !NET6_0_OR_GREATER
         [PrePrepareMethod]
 #endif
-        public override int Wait(IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout)
-        {
-            return UnmanagedMethods.WaitForMultipleObjectsEx(waitHandles.Length, waitHandles, waitAll,
-                millisecondsTimeout, false);
-        }
+        public override int Wait(IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout) =>
+            _impl.Wait(waitHandles, waitAll, millisecondsTimeout);
 
         public void Dispose() => SetSynchronizationContext(_inner);
 
-        public static IDisposable? Use()
+        internal static IDisposable? Use(NonPumpingLockHelper.IHelperImpl impl)
         {
             var current = Current;
             if (current == null)
@@ -67,12 +65,8 @@ namespace Avalonia.Win32
             if (current is NonPumpingSyncContext)
                 return null;
 
-            return new NonPumpingSyncContext(current);
-        }
-
-        internal class HelperImpl : NonPumpingLockHelper.IHelperImpl
-        {
-            IDisposable? NonPumpingLockHelper.IHelperImpl.Use() => NonPumpingSyncContext.Use();
+            return new NonPumpingSyncContext(impl, current);
         }
+        
     }
 }
diff --git a/src/Avalonia.Base/Utilities/NonPumpingLockHelper.cs b/src/Avalonia.Base/Utilities/NonPumpingLockHelper.cs
index 4cc1ba5190..55fd9a7957 100644
--- a/src/Avalonia.Base/Utilities/NonPumpingLockHelper.cs
+++ b/src/Avalonia.Base/Utilities/NonPumpingLockHelper.cs
@@ -1,4 +1,5 @@
 using System;
+using Avalonia.Threading;
 
 namespace Avalonia.Utilities
 {
@@ -6,9 +7,15 @@ namespace Avalonia.Utilities
     {
         public interface IHelperImpl
         {
-            IDisposable? Use();
+            int Wait(IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout);
         }
 
-        public static IDisposable? Use() => AvaloniaLocator.Current.GetService<IHelperImpl>()?.Use();
+        public static IDisposable? Use()
+        {
+            var impl = AvaloniaLocator.Current.GetService<IHelperImpl>();
+            if (impl == null)
+                return null;
+            return NonPumpingSyncContext.Use(impl);
+        }
     }
 }
diff --git a/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj b/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj
index 92ebbd57b8..2c5f3e2ed1 100644
--- a/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj
+++ b/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj
@@ -28,7 +28,7 @@
     <NoWarn>$(NoWarn);CA1416</NoWarn>
   </PropertyGroup>
   <ItemGroup>
-    <InternalsVisibleTo Include="Avalonia.Win32.Interop, PublicKey=$(AvaloniaPublicKey)"/>
-    <InternalsVisibleTo Include="Avalonia.Direct2D1, PublicKey=$(AvaloniaPublicKey)"/>
+    <InternalsVisibleTo Include="Avalonia.Win32.Interop, PublicKey=$(AvaloniaPublicKey)" />
+    <InternalsVisibleTo Include="Avalonia.Direct2D1, PublicKey=$(AvaloniaPublicKey)" />
   </ItemGroup>
 </Project>
diff --git a/src/Windows/Avalonia.Win32/NonPumpingWaitHelperImpl.cs b/src/Windows/Avalonia.Win32/NonPumpingWaitHelperImpl.cs
new file mode 100644
index 0000000000..bda2d441ad
--- /dev/null
+++ b/src/Windows/Avalonia.Win32/NonPumpingWaitHelperImpl.cs
@@ -0,0 +1,13 @@
+using System;
+using Avalonia.Utilities;
+using Avalonia.Win32.Interop;
+
+namespace Avalonia.Win32;
+
+internal class NonPumpingWaitHelperImpl : NonPumpingLockHelper.IHelperImpl
+{
+    public static NonPumpingWaitHelperImpl Instance { get; } = new();
+    public int Wait(IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout) =>
+        UnmanagedMethods.WaitForMultipleObjectsEx(waitHandles.Length, waitHandles, waitAll,
+            millisecondsTimeout, false);
+}
\ No newline at end of file
diff --git a/src/Windows/Avalonia.Win32/Win32Platform.cs b/src/Windows/Avalonia.Win32/Win32Platform.cs
index 857af3a783..7ce599c6bf 100644
--- a/src/Windows/Avalonia.Win32/Win32Platform.cs
+++ b/src/Windows/Avalonia.Win32/Win32Platform.cs
@@ -171,7 +171,7 @@ namespace Avalonia.Win32
                     }
                 })
                 .Bind<IPlatformIconLoader>().ToConstant(s_instance)
-                .Bind<NonPumpingLockHelper.IHelperImpl>().ToConstant(new NonPumpingSyncContext.HelperImpl())
+                .Bind<NonPumpingLockHelper.IHelperImpl>().ToConstant(NonPumpingWaitHelperImpl.Instance)
                 .Bind<IMountedVolumeInfoProvider>().ToConstant(new WindowsMountedVolumeInfoProvider())
                 .Bind<IPlatformLifetimeEventsImpl>().ToConstant(s_instance);
             
diff --git a/src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs b/src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs
index 2a40eb9f5b..39bdb942e1 100644
--- a/src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs
+++ b/src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs
@@ -579,7 +579,7 @@ namespace Avalonia.Win32
 
                 case WindowsMessage.WM_PAINT:
                     {
-                        using (NonPumpingSyncContext.Use())
+                        using (NonPumpingSyncContext.Use(NonPumpingWaitHelperImpl.Instance))
                         using (_rendererLock.Lock())
                         {
                             if (BeginPaint(_hwnd, out PAINTSTRUCT ps) != IntPtr.Zero)
@@ -602,7 +602,7 @@ namespace Avalonia.Win32
 
                 case WindowsMessage.WM_SIZE:
                     {
-                        using (NonPumpingSyncContext.Use())
+                        using (NonPumpingSyncContext.Use(NonPumpingWaitHelperImpl.Instance))
                         using (_rendererLock.Lock())
                         {
                             // Do nothing here, just block until the pending frame render is completed on the render thread
diff --git a/tests/Avalonia.Base.UnitTests/DispatcherTests.cs b/tests/Avalonia.Base.UnitTests/DispatcherTests.cs
index e429544172..9ba3f3980d 100644
--- a/tests/Avalonia.Base.UnitTests/DispatcherTests.cs
+++ b/tests/Avalonia.Base.UnitTests/DispatcherTests.cs
@@ -4,6 +4,7 @@ using System.Diagnostics;
 using System.Linq;
 using System.Threading;
 using Avalonia.Threading;
+using Avalonia.Utilities;
 using Xunit;
 namespace Avalonia.Base.UnitTests;
 
@@ -254,4 +255,207 @@ public class DispatcherTests
             Assert.Equal(foreground ? 0 : 1, ((SimpleControlledDispatcherImpl)impl).RunLoopCount);
     }
 
+
+    class DispatcherServices : IDisposable
+    {
+        private readonly IDisposable _scope;
+
+        public DispatcherServices(IDispatcherImpl impl)
+        {
+            _scope = AvaloniaLocator.EnterScope();
+            AvaloniaLocator.CurrentMutable.Bind<IDispatcherImpl>().ToConstant(impl);
+            Dispatcher.ResetForUnitTests();
+            SynchronizationContext.SetSynchronizationContext(null);
+        }
+        
+        public void Dispose()
+        {
+            Dispatcher.ResetForUnitTests();
+            _scope.Dispose();
+            SynchronizationContext.SetSynchronizationContext(null);
+        }
+    }
+    
+    [Fact]
+    public void ExitAllFramesShouldExitAllFramesAndBeAbleToContinue()
+    {
+        using (new DispatcherServices(new SimpleControlledDispatcherImpl()))
+        {
+            var actions = new List<string>();
+            var disp = Dispatcher.UIThread;
+            disp.Post(() =>
+            {
+                actions.Add("Nested frame");
+                Dispatcher.UIThread.MainLoop(CancellationToken.None);
+                actions.Add("Nested frame exited");
+            });
+            disp.Post(() =>
+            {
+                actions.Add("ExitAllFrames");
+                disp.ExitAllFrames();
+            });
+
+
+            disp.MainLoop(CancellationToken.None);
+            
+            Assert.Equal(new[] { "Nested frame", "ExitAllFrames", "Nested frame exited" }, actions);
+            actions.Clear();
+            
+            var secondLoop = new CancellationTokenSource();
+            disp.Post(() =>
+            {
+                actions.Add("Callback after exit");
+                secondLoop.Cancel();
+            });
+            disp.MainLoop(secondLoop.Token);
+            Assert.Equal(new[] { "Callback after exit" }, actions);
+        }
+    }
+    
+        
+    [Fact]
+    public void ShutdownShouldExitAllFramesAndNotAllowNewFrames()
+    {
+        using (new DispatcherServices(new SimpleControlledDispatcherImpl()))
+        {
+            var actions = new List<string>();
+            var disp = Dispatcher.UIThread;
+            disp.Post(() =>
+            {
+                actions.Add("Nested frame");
+                Dispatcher.UIThread.MainLoop(CancellationToken.None);
+                actions.Add("Nested frame exited");
+            });
+            disp.Post(() =>
+            {
+                actions.Add("Shutdown");
+                disp.BeginInvokeShutdown(DispatcherPriority.Normal);
+            });
+            
+            disp.Post(() =>
+            {
+                actions.Add("Nested frame after shutdown");
+                // This should exit immediately and not run any jobs
+                Dispatcher.UIThread.MainLoop(CancellationToken.None);
+                actions.Add("Nested frame after shutdown exited");
+            });
+            
+            var criticalFrameAfterShutdown = new DispatcherFrame(false);
+            disp.Post(() =>
+            {
+                actions.Add("Critical frame after shutdown");
+                
+                Dispatcher.UIThread.PushFrame(criticalFrameAfterShutdown);
+                actions.Add("Critical frame after shutdown exited");
+            });
+            disp.Post(() =>
+            {
+                actions.Add("Stop critical frame");
+                criticalFrameAfterShutdown.Continue = false;
+            });
+
+            disp.MainLoop(CancellationToken.None);
+
+            Assert.Equal(new[]
+            {
+                "Nested frame", 
+                "Shutdown",
+                // Normal nested frames are supposed to exit immediately
+                "Nested frame after shutdown", "Nested frame after shutdown exited",
+                // if frame is configured to not answer dispatcher requests, it should be allowed to run
+                "Critical frame after shutdown", "Stop critical frame", "Critical frame after shutdown exited",
+                // After 3-rd level frames have exited, the normal nested frame exits too
+                "Nested frame exited"
+            }, actions);
+            actions.Clear();
+            
+            disp.Post(()=>actions.Add("Frame after shutdown finished"));
+            Assert.Throws<InvalidOperationException>(() => disp.MainLoop(CancellationToken.None));
+            Assert.Empty(actions);
+        }
+    }
+
+    class WaitHelper : SynchronizationContext, NonPumpingLockHelper.IHelperImpl
+    {
+        public int WaitCount;
+        public int Wait(IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout)
+        {
+            WaitCount++;
+            return base.Wait(waitHandles, waitAll, millisecondsTimeout);
+        }
+    }
+    
+    [Fact]
+    public void DisableProcessingShouldStopProcessing()
+    {
+        using (new DispatcherServices(new SimpleControlledDispatcherImpl()))
+        {
+            var helper = new WaitHelper();
+            AvaloniaLocator.CurrentMutable.Bind<NonPumpingLockHelper.IHelperImpl>().ToConstant(helper);
+            using (Dispatcher.UIThread.DisableProcessing())
+            {
+                Assert.True(SynchronizationContext.Current is NonPumpingSyncContext);
+                Assert.Throws<InvalidOperationException>(() => Dispatcher.UIThread.MainLoop(CancellationToken.None));
+                Assert.Throws<InvalidOperationException>(() => Dispatcher.UIThread.RunJobs());
+            }
+
+            var avaloniaContext = new AvaloniaSynchronizationContext(true);
+            SynchronizationContext.SetSynchronizationContext(avaloniaContext);
+
+            var waitHandle = new ManualResetEvent(true);
+            
+            helper.WaitCount = 0;
+            waitHandle.WaitOne(100);
+            Assert.Equal(0, helper.WaitCount);
+            using (Dispatcher.UIThread.DisableProcessing())
+            {
+                Assert.Equal(avaloniaContext, SynchronizationContext.Current);
+                waitHandle.WaitOne(100);
+                Assert.Equal(1, helper.WaitCount);
+            }
+        }
+    }
+
+    [Fact]
+    public void DispatcherOperationsHaveContextWithProperPriority()
+    {
+        using (new DispatcherServices(new SimpleControlledDispatcherImpl()))
+        {
+            SynchronizationContext.SetSynchronizationContext(null);
+            var disp = Dispatcher.UIThread;
+            var priorities = new List<DispatcherPriority>();
+
+            void DumpCurrentPriority() =>
+                priorities.Add(((AvaloniaSynchronizationContext)SynchronizationContext.Current!).Priority);
+                
+                
+            disp.Post(DumpCurrentPriority, DispatcherPriority.Normal);
+            disp.Post(DumpCurrentPriority, DispatcherPriority.Loaded);
+            disp.Post(DumpCurrentPriority, DispatcherPriority.Input);
+            disp.Post(() =>
+            {
+                DumpCurrentPriority();
+                disp.ExitAllFrames();
+            }, DispatcherPriority.Background);
+            disp.MainLoop(CancellationToken.None);
+
+            disp.Invoke(DumpCurrentPriority, DispatcherPriority.Send);
+            disp.Invoke(() =>
+            {
+                DumpCurrentPriority();
+                return 1;
+            }, DispatcherPriority.Send);
+
+            Assert.Equal(
+                new[]
+                {
+                    DispatcherPriority.Normal, DispatcherPriority.Loaded, DispatcherPriority.Input, DispatcherPriority.Background,
+                    DispatcherPriority.Send, DispatcherPriority.Send,
+                },
+                priorities);
+
+
+        }
+    }
+
 }
\ No newline at end of file

From 9d4f11a1119d86e84daae2077da3f7a3d3acadc8 Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sat, 25 Mar 2023 17:05:03 +0600
Subject: [PATCH 31/40] Fixed tests

---
 .../Threading/DispatcherOperation.cs          |  4 +--
 .../ClassicDesktopStyleApplicationLifetime.cs |  1 +
 .../DesktopStyleApplicationLifetimeTests.cs   | 26 +++++++++++++------
 3 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/src/Avalonia.Base/Threading/DispatcherOperation.cs b/src/Avalonia.Base/Threading/DispatcherOperation.cs
index 01652fb731..9fe99e5db4 100644
--- a/src/Avalonia.Base/Threading/DispatcherOperation.cs
+++ b/src/Avalonia.Base/Threading/DispatcherOperation.cs
@@ -105,9 +105,7 @@ public class DispatcherOperation
     {
         lock (Dispatcher.InstanceLock)
         {
-            if (Status == DispatcherOperationStatus.Pending)
-                return;
-            Dispatcher.Abort(this);
+            if (Status == DispatcherOperationStatus.Pending) Dispatcher.Abort(this);
         }
     }
 
diff --git a/src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs b/src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs
index ada0b94124..16fc46563f 100644
--- a/src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs
+++ b/src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs
@@ -184,6 +184,7 @@ namespace Avalonia.Controls.ApplicationLifetimes
                 _cts?.Cancel();
                 _cts = null;
                 _isShuttingDown = false;
+                Dispatcher.UIThread.BeginInvokeShutdown(DispatcherPriority.Send);
             }
 
             return true;
diff --git a/tests/Avalonia.Controls.UnitTests/DesktopStyleApplicationLifetimeTests.cs b/tests/Avalonia.Controls.UnitTests/DesktopStyleApplicationLifetimeTests.cs
index 90a0db691c..58811cd081 100644
--- a/tests/Avalonia.Controls.UnitTests/DesktopStyleApplicationLifetimeTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/DesktopStyleApplicationLifetimeTests.cs
@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Generic;
+using System.Threading;
 using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Controls.Platform;
 using Avalonia.Platform;
 using Avalonia.Rendering;
 using Avalonia.Threading;
@@ -13,17 +15,22 @@ namespace Avalonia.Controls.UnitTests
     
     public class DesktopStyleApplicationLifetimeTests
     {
-        IDispatcherImpl CreateDispatcherWithInstantMainLoop() => Mock.Of<IControlledDispatcherImpl>(x => x.CurrentThreadIsLoopThread == true);
-
-
+        IDispatcherImpl CreateDispatcherWithInstantMainLoop()
+        {
+            var mock = new Mock<IControlledDispatcherImpl>();
+            mock.Setup(x => x.RunLoop(It.IsAny<CancellationToken>()))
+                .Callback(() => Dispatcher.UIThread.ExitAllFrames());
+            mock.Setup(x => x.CurrentThreadIsLoopThread).Returns(true);
+            return mock.Object;
+        }
+        
         [Fact]
         public void Should_Set_ExitCode_After_Shutdown()
         {
-            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: CreateDispatcherWithInstantMainLoop())))
+            using (UnitTestApplication.Start(new TestServices(dispatcherImpl: new ManagedDispatcherImpl(null))))
             using(var lifetime = new ClassicDesktopStyleApplicationLifetime())    
             {
-                lifetime.Shutdown(1337);
-
+                Dispatcher.UIThread.Post(() => lifetime.Shutdown(1337));
                 var exitCode = lifetime.Start(Array.Empty<string>());
 
                 Assert.Equal(1337, exitCode);
@@ -219,11 +226,14 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Should_Allow_Canceling_Shutdown_Via_ShutdownRequested_Event()
         {
-            using (UnitTestApplication.Start(TestServices.StyledWindow.With(dispatcherImpl: CreateDispatcherWithInstantMainLoop())))
+            using (UnitTestApplication.Start(TestServices.StyledWindow.With(dispatcherImpl: new ManagedDispatcherImpl(null))))
             using (var lifetime = new ClassicDesktopStyleApplicationLifetime())
             {
                 var lifetimeEvents = new Mock<IPlatformLifetimeEventsImpl>();
                 AvaloniaLocator.CurrentMutable.Bind<IPlatformLifetimeEventsImpl>().ToConstant(lifetimeEvents.Object);
+                
+                // Force exit immediately
+                Dispatcher.UIThread.Post(Dispatcher.UIThread.ExitAllFrames);
                 lifetime.Start(Array.Empty<string>());
 
                 var window = new Window();
@@ -356,7 +366,7 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void Shutdown_NotCancellable_By_Preventing_Window_Close()
         {
-            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            using (UnitTestApplication.Start(TestServices.StyledWindow.With(dispatcherImpl: CreateDispatcherWithInstantMainLoop())))
             using(var lifetime = new ClassicDesktopStyleApplicationLifetime())
             {
                 var hasExit = false;

From 91e4bd00b6b842006bbb455693df29ae5935ee06 Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sat, 25 Mar 2023 17:52:28 +0600
Subject: [PATCH 32/40] Fixed more tests

---
 src/Avalonia.Controls/Control.cs                 | 8 ++++++++
 tests/Avalonia.Controls.UnitTests/LoadedTests.cs | 4 ++++
 tests/Avalonia.UnitTests/UnitTestApplication.cs  | 6 +++++-
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/Avalonia.Controls/Control.cs b/src/Avalonia.Controls/Control.cs
index 325593508c..621bdd1017 100644
--- a/src/Avalonia.Controls/Control.cs
+++ b/src/Avalonia.Controls/Control.cs
@@ -527,5 +527,13 @@ namespace Avalonia.Controls
                 }
             }
         }
+
+        // Since we are resetting the dispatcher instance, the callback might never arrive
+        internal static void ResetLoadedQueueForUnitTests()
+        {
+            _loadedQueue.Clear();
+            _loadedProcessingQueue.Clear();
+            _isLoadedProcessing = false;
+        }
     }
 }
diff --git a/tests/Avalonia.Controls.UnitTests/LoadedTests.cs b/tests/Avalonia.Controls.UnitTests/LoadedTests.cs
index aaf0dce30e..555ba02409 100644
--- a/tests/Avalonia.Controls.UnitTests/LoadedTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/LoadedTests.cs
@@ -11,6 +11,8 @@ public class LoadedTests
     [Fact]
     public void Window_Loads_And_Unloads()
     {
+        // Some other tests are populating the queue and are not resetting the dispatcher, so we need to purge it
+        Control.ResetLoadedQueueForUnitTests();
         using (UnitTestApplication.Start(TestServices.StyledWindow))
         {
             int loadedCount = 0, unloadedCount = 0;
@@ -40,6 +42,8 @@ public class LoadedTests
     [Fact]
     public void Control_Loads_And_Unloads()
     {
+        // Some other tests are populating the queue and are not resetting the dispatcher, so we need to purge it
+        Control.ResetLoadedQueueForUnitTests();
         using (UnitTestApplication.Start(TestServices.StyledWindow))
         {
             int loadedCount = 0, unloadedCount = 0;
diff --git a/tests/Avalonia.UnitTests/UnitTestApplication.cs b/tests/Avalonia.UnitTests/UnitTestApplication.cs
index 8d9f08caa1..32e597781c 100644
--- a/tests/Avalonia.UnitTests/UnitTestApplication.cs
+++ b/tests/Avalonia.UnitTests/UnitTestApplication.cs
@@ -8,6 +8,7 @@ using Avalonia.Rendering;
 using Avalonia.Threading;
 using System.Reactive.Disposables;
 using System.Reactive.Concurrency;
+using System.Threading;
 using Avalonia.Input.Platform;
 using Avalonia.Animation;
 using Avalonia.Media;
@@ -42,7 +43,9 @@ namespace Avalonia.UnitTests
         public static IDisposable Start(TestServices services = null)
         {
             var scope = AvaloniaLocator.EnterScope();
-            var app = new UnitTestApplication(services);
+            SynchronizationContext.SetSynchronizationContext(null);
+            AvaloniaSynchronizationContext.InstallIfNeeded();
+            _ = new UnitTestApplication(services);
             Dispatcher.ResetForUnitTests();
             return Disposable.Create(() =>
             {
@@ -53,6 +56,7 @@ namespace Avalonia.UnitTests
 
                 scope.Dispose();
                 Dispatcher.ResetForUnitTests();
+                SynchronizationContext.SetSynchronizationContext(null);
             });
         }
 

From 44a830fd7f8ec57bff18049a6f579fe663333a30 Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sat, 25 Mar 2023 18:24:55 +0600
Subject: [PATCH 33/40] Fixed tests

---
 tests/Avalonia.UnitTests/UnitTestApplication.cs | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tests/Avalonia.UnitTests/UnitTestApplication.cs b/tests/Avalonia.UnitTests/UnitTestApplication.cs
index 32e597781c..870e6391d0 100644
--- a/tests/Avalonia.UnitTests/UnitTestApplication.cs
+++ b/tests/Avalonia.UnitTests/UnitTestApplication.cs
@@ -43,8 +43,7 @@ namespace Avalonia.UnitTests
         public static IDisposable Start(TestServices services = null)
         {
             var scope = AvaloniaLocator.EnterScope();
-            SynchronizationContext.SetSynchronizationContext(null);
-            AvaloniaSynchronizationContext.InstallIfNeeded();
+            var oldContext = SynchronizationContext.Current;
             _ = new UnitTestApplication(services);
             Dispatcher.ResetForUnitTests();
             return Disposable.Create(() =>
@@ -56,7 +55,7 @@ namespace Avalonia.UnitTests
 
                 scope.Dispose();
                 Dispatcher.ResetForUnitTests();
-                SynchronizationContext.SetSynchronizationContext(null);
+                SynchronizationContext.SetSynchronizationContext(oldContext);
             });
         }
 

From 7d63f5f5460e2f007bb342afce639c63f6462551 Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sat, 25 Mar 2023 20:41:21 +0600
Subject: [PATCH 34/40] InvokeShutdown

---
 src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs          | 6 ++++++
 .../ClassicDesktopStyleApplicationLifetime.cs               | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs b/src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs
index cabbabcf6b..cfb1cb7e2f 100644
--- a/src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs
+++ b/src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs
@@ -97,6 +97,12 @@ public partial class Dispatcher
     /// </summary>
     public void BeginInvokeShutdown(DispatcherPriority priority) => Post(StartShutdownImpl, priority);
 
+    
+    /// <summary>
+    /// Initiates the shutdown process of the Dispatcher synchronously.
+    /// </summary>
+    public void InvokeShutdown() => Invoke(StartShutdownImpl, DispatcherPriority.Send);
+
     private void StartShutdownImpl()
     {
         if (!_startingShutdown)
diff --git a/src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs b/src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs
index 16fc46563f..9cc36e6a81 100644
--- a/src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs
+++ b/src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs
@@ -184,7 +184,7 @@ namespace Avalonia.Controls.ApplicationLifetimes
                 _cts?.Cancel();
                 _cts = null;
                 _isShuttingDown = false;
-                Dispatcher.UIThread.BeginInvokeShutdown(DispatcherPriority.Send);
+                Dispatcher.UIThread.InvokeShutdown();
             }
 
             return true;

From 3d78754f2e80c81851039dffe7a27b644067caec Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sat, 25 Mar 2023 21:00:24 +0600
Subject: [PATCH 35/40] Call Array.Clear immediately when returning it to the
 pool

---
 .../Composition/Transport/BatchStreamArrayPool.cs         | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/Avalonia.Base/Rendering/Composition/Transport/BatchStreamArrayPool.cs b/src/Avalonia.Base/Rendering/Composition/Transport/BatchStreamArrayPool.cs
index 032a3046d7..8916983a5c 100644
--- a/src/Avalonia.Base/Rendering/Composition/Transport/BatchStreamArrayPool.cs
+++ b/src/Avalonia.Base/Rendering/Composition/Transport/BatchStreamArrayPool.cs
@@ -72,6 +72,11 @@ internal abstract class BatchStreamPoolBase<T> : IDisposable
 
     protected abstract T CreateItem();
 
+    protected virtual void ClearItem(T item)
+    {
+        
+    }
+
     protected virtual void DestroyItem(T item)
     {
         
@@ -94,6 +99,7 @@ internal abstract class BatchStreamPoolBase<T> : IDisposable
 
     public void Return(T item)
     {
+        ClearItem(item);
         lock (_pool)
         {
             _usage--;
@@ -138,7 +144,7 @@ internal sealed class BatchStreamObjectPool<T> : BatchStreamPoolBase<T[]> where
         return new T[ArraySize];
     }
 
-    protected override void DestroyItem(T[] item)
+    protected override void ClearItem(T[] item)
     {
         Array.Clear(item, 0, item.Length);
     }

From b75bc80ba3a89fba7e3752486c6cf3b5a7102aa7 Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sat, 25 Mar 2023 21:50:16 +0600
Subject: [PATCH 36/40] fix

---
 src/Avalonia.Base/Threading/DispatcherOperation.cs | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/Avalonia.Base/Threading/DispatcherOperation.cs b/src/Avalonia.Base/Threading/DispatcherOperation.cs
index 9fe99e5db4..809c41ff02 100644
--- a/src/Avalonia.Base/Threading/DispatcherOperation.cs
+++ b/src/Avalonia.Base/Threading/DispatcherOperation.cs
@@ -101,11 +101,14 @@ public class DispatcherOperation
         }
     }
     
-    public void Abort()
+    public bool Abort()
     {
         lock (Dispatcher.InstanceLock)
         {
-            if (Status == DispatcherOperationStatus.Pending) Dispatcher.Abort(this);
+            if (Status != DispatcherOperationStatus.Pending)
+                return false;
+            Dispatcher.Abort(this);
+            return true;
         }
     }
 

From 9119ac851301e8c6a48de0b0051f25b1b67c3d9a Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sat, 25 Mar 2023 22:08:46 +0600
Subject: [PATCH 37/40] fix

---
 src/Avalonia.Base/Threading/Dispatcher.Invoke.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs b/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
index 68f9cc7e2e..c6e9203f70 100644
--- a/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
+++ b/src/Avalonia.Base/Threading/Dispatcher.Invoke.cs
@@ -391,7 +391,7 @@ public partial class Dispatcher
         return operation;
     }
 
-    private void InvokeAsyncImpl(DispatcherOperation operation, CancellationToken cancellationToken)
+    internal void InvokeAsyncImpl(DispatcherOperation operation, CancellationToken cancellationToken)
     {
         bool succeeded = false;
 

From e29e43793f9730bb649c4190bc694120ae151093 Mon Sep 17 00:00:00 2001
From: Max Katz <maxkatz6@outlook.com>
Date: Sun, 26 Mar 2023 15:56:32 +0900
Subject: [PATCH 38/40] Fix menu placement

---
 src/Avalonia.Themes.Fluent/Controls/MenuItem.xaml | 2 +-
 src/Avalonia.Themes.Simple/Controls/MenuItem.xaml | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Avalonia.Themes.Fluent/Controls/MenuItem.xaml b/src/Avalonia.Themes.Fluent/Controls/MenuItem.xaml
index 5a10c62860..76dec10b69 100644
--- a/src/Avalonia.Themes.Fluent/Controls/MenuItem.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/MenuItem.xaml
@@ -118,7 +118,7 @@
           </Border>
           <Popup Name="PART_Popup"
                  WindowManagerAddShadowHint="False"
-                 Placement="Right"
+                 Placement="RightEdgeAlignedTop"
                  HorizontalOffset="{DynamicResource MenuFlyoutSubItemPopupHorizontalOffset}"
                  IsLightDismissEnabled="False"
                  IsOpen="{TemplateBinding IsSubMenuOpen, Mode=TwoWay}">
diff --git a/src/Avalonia.Themes.Simple/Controls/MenuItem.xaml b/src/Avalonia.Themes.Simple/Controls/MenuItem.xaml
index 7ec666eaf9..2f09b9dc40 100644
--- a/src/Avalonia.Themes.Simple/Controls/MenuItem.xaml
+++ b/src/Avalonia.Themes.Simple/Controls/MenuItem.xaml
@@ -65,7 +65,7 @@
                    IsLightDismissEnabled="False"
                    IsOpen="{TemplateBinding IsSubMenuOpen,
                                             Mode=TwoWay}"
-                   Placement="Right">
+                   Placement="RightEdgeAlignedTop">
               <Border Background="{DynamicResource ThemeBackgroundBrush}"
                       BorderBrush="{DynamicResource ThemeBorderMidBrush}"
                       BorderThickness="{TemplateBinding BorderThickness}">

From 6ad2f2a2f4a5ab183f5f125de9df197281eb9720 Mon Sep 17 00:00:00 2001
From: Nikita Tsukanov <keks9n@gmail.com>
Date: Sun, 26 Mar 2023 13:37:11 +0600
Subject: [PATCH 39/40] non-private set

---
 src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs b/src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs
index cfb1cb7e2f..e1833fef2b 100644
--- a/src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs
+++ b/src/Avalonia.Base/Threading/Dispatcher.MainLoop.cs
@@ -9,7 +9,7 @@ public partial class Dispatcher
 {
     internal bool ExitAllFramesRequested { get; private set; }
     internal bool HasShutdownStarted { get; private set; }
-    internal int DisabledProcessingCount { get; private set; }
+    internal int DisabledProcessingCount { get; set; }
     private bool _hasShutdownFinished;
     private bool _startingShutdown;
     

From 3ac7760b3af1abfc4dcbd40c81eec9c93b681f6d Mon Sep 17 00:00:00 2001
From: Emmanuel Hansen <emmausssss@gmail.com>
Date: Mon, 27 Mar 2023 11:45:20 +0000
Subject: [PATCH 40/40] don't create an input connection if client is null

---
 src/Android/Avalonia.Android/AndroidInputMethod.cs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/Android/Avalonia.Android/AndroidInputMethod.cs b/src/Android/Avalonia.Android/AndroidInputMethod.cs
index 27dcfe8645..39b58c50c1 100644
--- a/src/Android/Avalonia.Android/AndroidInputMethod.cs
+++ b/src/Android/Avalonia.Android/AndroidInputMethod.cs
@@ -1,7 +1,6 @@
 using System;
 using Android.Content;
 using Android.Runtime;
-using Android.Text;
 using Android.Views;
 using Android.Views.InputMethods;
 using Avalonia.Android.Platform.SkiaPlatform;
@@ -99,6 +98,9 @@ namespace Avalonia.Android
         {
             _host.InitEditorInfo((topLevel, outAttrs) =>
             {
+                if (_client == null)
+                    return null;
+
                 _inputConnection = new AvaloniaInputConnection(topLevel, this);
 
                 outAttrs.InputType = options.ContentType switch