Merge branch 'master' into feat/SelectedValue_SelectedValueBinding

build/ImageSharp.props

@@ -1,5 +1,5 @@
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup>
-    <PackageReference Include="SixLabors.ImageSharp" Version="2.1.1" />
+    <PackageReference Include="SixLabors.ImageSharp" Version="2.1.3" />
   </ItemGroup>
 </Project>

build/Moq.props

@@ -1,5 +1,5 @@
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup>
-    <PackageReference Include="Moq" Version="4.14.1" />
+    <PackageReference Include="Moq" Version="4.18.4" />
   </ItemGroup>
 </Project>

build/XUnit.props

@@ -1,13 +1,12 @@
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup>
-    <PackageReference Include="xunit" Version="2.4.1" />
-    <PackageReference Include="xunit.abstractions" Version="2.0.3" />
-    <PackageReference Include="xunit.assert" Version="2.4.1" />
-    <PackageReference Include="xunit.core" Version="2.4.1" />
-    <PackageReference Include="xunit.extensibility.core" Version="2.4.1" />
-    <PackageReference Include="xunit.extensibility.execution" Version="2.4.1" />
-    <PackageReference Include="xunit.runner.console" Version="2.4.1" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" />
+    <PackageReference Include="xunit" Version="2.4.2" />
+    <PackageReference Include="xunit.assert" Version="2.4.2" />
+    <PackageReference Include="xunit.core" Version="2.4.2" />
+    <PackageReference Include="xunit.extensibility.core" Version="2.4.2" />
+    <PackageReference Include="xunit.extensibility.execution" Version="2.4.2" />
+    <PackageReference Include="xunit.runner.console" Version="2.4.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5" />
     <PackageReference Include="Xunit.SkippableFact" Version="1.4.13" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.7.0" />
   </ItemGroup>

src/Avalonia.Base/Animation/KeySpline.cs

@@ -79,15 +79,12 @@ namespace Avalonia.Animation
         /// <param name="culture">culture of the string</param>
         /// <exception cref="FormatException">Thrown if the string does not have 4 values</exception>
         /// <returns>A <see cref="KeySpline"/> with the appropriate values set</returns>
-        public static KeySpline Parse(string value, CultureInfo culture)
+        public static KeySpline Parse(string value, CultureInfo? culture)
         {
-            if (culture is null)
-                culture = CultureInfo.InvariantCulture;
+            culture ??= CultureInfo.InvariantCulture;
 
-            using (var tokenizer = new StringTokenizer((string)value, culture, exceptionMessage: $"Invalid KeySpline string: \"{value}\"."))
-            {
-                return new KeySpline(tokenizer.ReadDouble(), tokenizer.ReadDouble(), tokenizer.ReadDouble(), tokenizer.ReadDouble());
-            }
+            using var tokenizer = new StringTokenizer(value, culture, exceptionMessage: $"Invalid KeySpline string: \"{value}\".");
+            return new KeySpline(tokenizer.ReadDouble(), tokenizer.ReadDouble(), tokenizer.ReadDouble(), tokenizer.ReadDouble());
         }
 
         /// <summary>

src/Avalonia.Base/AvaloniaObject.cs

@@ -152,7 +152,7 @@ namespace Avalonia
             property = property ?? throw new ArgumentNullException(nameof(property));
             VerifyAccess();
 
-            _values?.ClearLocalValue(property);
+            _values.ClearLocalValue(property);
         }
 
         /// <summary>
@@ -242,7 +242,14 @@ namespace Avalonia
             return registered.InvokeGetter(this);
         }
 
-        /// <inheritdoc/>
+        /// <summary>
+        /// Gets an <see cref="AvaloniaProperty"/> base value.
+        /// </summary>
+        /// <param name="property">The property.</param>
+        /// <remarks>
+        /// Gets the value of the property excluding animated values, otherwise <see cref="Optional{T}.Empty"/>.
+        /// Note that this method does not return property values that come from inherited or default values.
+        /// </remarks>
         public Optional<T> GetBaseValue<T>(StyledProperty<T> property)
         {
             _ = property ?? throw new ArgumentNullException(nameof(property));
@@ -261,7 +268,7 @@ namespace Avalonia
 
             VerifyAccess();
 
-            return _values?.IsAnimating(property) ?? false;
+            return _values.IsAnimating(property);
         }
 
         /// <summary>
@@ -279,7 +286,7 @@ namespace Avalonia
 
             VerifyAccess();
 
-            return _values?.IsSet(property) ?? false;
+            return _values.IsSet(property);
         }
 
         /// <summary>
@@ -515,14 +522,12 @@ namespace Avalonia
         /// <param name="property">The property.</param>
         public void CoerceValue(AvaloniaProperty property) => _values.CoerceValue(property);
 
-        /// <inheritdoc/>
         internal void AddInheritanceChild(AvaloniaObject child)
         {
             _inheritanceChildren ??= new List<AvaloniaObject>();
             _inheritanceChildren.Add(child);
         }
-        
-        /// <inheritdoc/>
+
         internal void RemoveInheritanceChild(AvaloniaObject child)
         {
             _inheritanceChildren?.Remove(child);
@@ -541,24 +546,11 @@ namespace Avalonia
                 return new AvaloniaPropertyValue(
                     property,
                     GetValue(property),
-                    BindingPriority.Unset,
-                    "Local Value");
-            }
-            else if (_values != null)
-            {
-                var result = _values.GetDiagnostic(property);
-
-                if (result != null)
-                {
-                    return result;
-                }
+                    BindingPriority.LocalValue,
+                    null);
             }
 
-            return new AvaloniaPropertyValue(
-                property,
-                GetValue(property),
-                BindingPriority.Unset,
-                "Unset");
+            return _values.GetDiagnostic(property);
         }
 
         internal ValueStore GetValueStore() => _values;

src/Avalonia.Base/Data/Converters/DefaultValueConverter.cs

@@ -30,7 +30,7 @@ namespace Avalonia.Data.Converters
         {
             if (value == null)
             {
-                return targetType.IsValueType ? AvaloniaProperty.UnsetValue : null;
+                return null;
             }
 
             if (typeof(ICommand).IsAssignableFrom(targetType) && value is Delegate d && d.Method.GetParameters().Length <= 1)

src/Avalonia.Base/Diagnostics/AvaloniaObjectExtensions.cs

@@ -1,6 +1,3 @@
-using System;
-using Avalonia.Data;
-
 namespace Avalonia.Diagnostics
 {
     /// <summary>

src/Avalonia.Base/Input/DragEventArgs.cs

@@ -1,36 +1,28 @@
 using System;
 using Avalonia.Interactivity;
 using Avalonia.Metadata;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Input
 {
     public class DragEventArgs : RoutedEventArgs
     {
-        private Interactive _target;
-        private Point _targetLocation;
+        private readonly Interactive _target;
+        private readonly Point _targetLocation;
 
         public DragDropEffects DragEffects { get; set; }
 
-        public IDataObject Data { get; private set; }
+        public IDataObject Data { get; }
 
-        public KeyModifiers KeyModifiers { get; private set; }
+        public KeyModifiers KeyModifiers { get; }
 
         public Point GetPosition(Visual relativeTo)
         {
-            var point = new Point(0, 0);
-
             if (relativeTo == null)
             {
                 throw new ArgumentNullException(nameof(relativeTo));
             }
 
-            if (_target != null)
-            {
-                point = _target.TranslatePoint(_targetLocation, relativeTo) ?? point;
-            }
-
-            return point;
+            return _target.TranslatePoint(_targetLocation, relativeTo) ?? new Point(0, 0);
         }
 
         [Unstable]

src/Avalonia.Base/Input/KeyGesture.cs

@@ -136,7 +136,7 @@ namespace Avalonia.Input
             return StringBuilderCache.GetStringAndRelease(s);
         }
 
-        public bool Matches(KeyEventArgs keyEvent) =>
+        public bool Matches(KeyEventArgs? keyEvent) =>
             keyEvent != null &&
             keyEvent.KeyModifiers == KeyModifiers &&
             ResolveNumPadOperationKey(keyEvent.Key) == ResolveNumPadOperationKey(Key);

src/Avalonia.Base/Input/KeyboardNavigationHandler.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
-using System.Linq;
 using Avalonia.Input.Navigation;
 using Avalonia.VisualTree;
 
@@ -51,7 +50,7 @@ namespace Avalonia.Input
 
             // If there's a custom keyboard navigation handler as an ancestor, use that.
             var custom = (element as Visual)?.FindAncestorOfType<ICustomKeyboardNavigation>(true);
-            if (custom is object && HandlePreCustomNavigation(custom, element, direction, out var ce))
+            if (custom is not null && HandlePreCustomNavigation(custom, element, direction, out var ce))
                 return ce;
 
             var result = direction switch
@@ -117,32 +116,27 @@ namespace Avalonia.Input
             NavigationDirection direction,
             [NotNullWhen(true)] out IInputElement? result)
         {
-            if (customHandler != null)
+            var (handled, next) = customHandler.GetNext(element, direction);
+
+            if (handled)
             {
-                var (handled, next) = customHandler.GetNext(element, direction);
+                if (next is not null)
+                {
+                    result = next;
+                    return true;
+                }
 
-                if (handled)
+                var r = direction switch
                 {
-                    if (next != null)
-                    {
-                        result = next;
-                        return true;
-                    }
-                    else if (direction == NavigationDirection.Next || direction == NavigationDirection.Previous)
-                    {
-                        var r = direction switch
-                        {
-                            NavigationDirection.Next => TabNavigation.GetNextTabOutside(customHandler),
-                            NavigationDirection.Previous => TabNavigation.GetPrevTabOutside(customHandler),
-                            _ => throw new NotSupportedException(),
-                        };
-
-                        if (r is object)
-                        {
-                            result = r;
-                            return true;
-                        }
-                    }
+                    NavigationDirection.Next => TabNavigation.GetNextTabOutside(customHandler),
+                    NavigationDirection.Previous => TabNavigation.GetPrevTabOutside(customHandler),
+                    _ => null
+                };
+
+                if (r is not null)
+                {
+                    result = r;
+                    return true;
                 }
             }
 

src/Avalonia.Base/Input/Navigation/TabNavigation.cs

@@ -1,6 +1,4 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
 using Avalonia.VisualTree;
 
 namespace Avalonia.Input.Navigation
@@ -54,8 +52,7 @@ namespace Avalonia.Input.Navigation
                 // Avoid the endless loop here for Cycle groups
                 if (loopStartElement == nextTabElement)
                     break;
-                if (loopStartElement == null)
-                    loopStartElement = nextTabElement;
+                loopStartElement ??= nextTabElement;
 
                 var firstTabElementInside = GetNextTab(null, nextTabElement, true);
                 if (firstTabElementInside != null)
@@ -80,12 +77,9 @@ namespace Avalonia.Input.Navigation
 
         public static IInputElement? GetNextTabOutside(ICustomKeyboardNavigation e)
         {
-            if (e is IInputElement container)
+            if (e is IInputElement container && GetLastInTree(container) is { } last)
             {
-                var last = GetLastInTree(container);
-
-                if (last is object)
-                    return GetNextTab(last, false);
+                return GetNextTab(last, false);
             }
 
             return null;
@@ -93,11 +87,8 @@ namespace Avalonia.Input.Navigation
 
         public static IInputElement? GetPrevTab(IInputElement? e, IInputElement? container, bool goDownOnly)
         {
-            if (e is null && container is null)
-                throw new InvalidOperationException("Either 'e' or 'container' must be non-null.");
-
-            if (container is null)
-                container = GetGroupParent(e!);
+            container ??=
+                GetGroupParent(e ?? throw new InvalidOperationException("Either 'e' or 'container' must be non-null."));
 
             KeyboardNavigationMode tabbingType = GetKeyNavigationMode(container);
 
@@ -163,8 +154,7 @@ namespace Avalonia.Input.Navigation
                 // Avoid the endless loop here
                 if (loopStartElement == nextTabElement)
                     break;
-                if (loopStartElement == null)
-                    loopStartElement = nextTabElement;
+                loopStartElement ??= nextTabElement;
 
                 // At this point nextTabElement is TabGroup
                 var lastTabElementInside = GetPrevTab(null, nextTabElement, true);
@@ -189,22 +179,18 @@ namespace Avalonia.Input.Navigation
 
         public static IInputElement? GetPrevTabOutside(ICustomKeyboardNavigation e)
         {
-            if (e is IInputElement container)
+            if (e is IInputElement container && GetFirstChild(container) is { } first)
             {
-                var first = GetFirstChild(container);
-
-                if (first is object)
-                    return GetPrevTab(first, null, false);
+                return GetPrevTab(first, null, false);
             }
 
             return null;
         }
 
-        private static IInputElement? FocusedElement(IInputElement e)
+        private static IInputElement? FocusedElement(IInputElement? e)
         {
-            var iie = e;
             // Focus delegation is enabled only if keyboard focus is outside the container
-            if (iie != null && !iie.IsKeyboardFocusWithin)
+            if (e != null && !e.IsKeyboardFocusWithin)
             {
                 var focusedElement = (FocusManager.Instance as FocusManager)?.GetFocusedElement(e);
                 if (focusedElement != null)
@@ -229,13 +215,11 @@ namespace Avalonia.Input.Navigation
         private static IInputElement? GetFirstChild(IInputElement e)
         {
             // If the element has a FocusedElement it should be its first child
-            if (FocusedElement(e) is IInputElement focusedElement)
+            if (FocusedElement(e) is { } focusedElement)
                 return focusedElement;
 
             // Return the first visible element.
-            var uiElement = e as InputElement;
-
-            if (uiElement is null || IsVisibleAndEnabled(uiElement))
+            if (e is not InputElement uiElement || IsVisibleAndEnabled(uiElement))
             {
                 if (e is Visual elementAsVisual)
                 {
@@ -265,7 +249,7 @@ namespace Avalonia.Input.Navigation
         private static IInputElement? GetLastChild(IInputElement e)
         {
             // If the element has a FocusedElement it should be its last child
-            if (FocusedElement(e) is IInputElement focusedElement)
+            if (FocusedElement(e) is { } focusedElement)
                 return focusedElement;
 
             // Return the last visible element.
@@ -273,9 +257,7 @@ namespace Avalonia.Input.Navigation
 
             if (uiElement == null || IsVisibleAndEnabled(uiElement))
             {
-                var elementAsVisual = e as Visual;
-
-                if (elementAsVisual != null)
+                if (e is Visual elementAsVisual)
                 {
                     var children = elementAsVisual.VisualChildren;
                     var count = children.Count;
@@ -322,7 +304,7 @@ namespace Avalonia.Input.Navigation
             return firstTabElement;
         }
 
-        private static IInputElement? GetLastInTree(IInputElement container)
+        private static IInputElement GetLastInTree(IInputElement container)
         {
             IInputElement? result;
             IInputElement? c = container;

src/Avalonia.Base/LogicalTree/LogicalExtensions.cs

@@ -48,7 +48,7 @@ namespace Avalonia.LogicalTree
         /// <param name="logical">The logical.</param>
         /// <param name="includeSelf">If given logical should be included in search.</param>
         /// <returns>First ancestor of given type.</returns>
-        public static T? FindLogicalAncestorOfType<T>(this ILogical logical, bool includeSelf = false) where T : class
+        public static T? FindLogicalAncestorOfType<T>(this ILogical? logical, bool includeSelf = false) where T : class
         {
             if (logical is null)
             {
@@ -120,7 +120,7 @@ namespace Avalonia.LogicalTree
         /// <param name="logical">The logical.</param>
         /// <param name="includeSelf">If given logical should be included in search.</param>
         /// <returns>First descendant of given type.</returns>
-        public static T? FindLogicalDescendantOfType<T>(this ILogical logical, bool includeSelf = false) where T : class
+        public static T? FindLogicalDescendantOfType<T>(this ILogical? logical, bool includeSelf = false) where T : class
         {
             if (logical is null)
             {
@@ -185,7 +185,7 @@ namespace Avalonia.LogicalTree
         /// True if <paramref name="logical"/> is an ancestor of <paramref name="target"/>;
         /// otherwise false.
         /// </returns>
-        public static bool IsLogicalAncestorOf(this ILogical logical, ILogical target)
+        public static bool IsLogicalAncestorOf(this ILogical? logical, ILogical? target)
         {
             var current = target?.LogicalParent;
 

src/Avalonia.Base/Media/Color.cs

@@ -147,16 +147,11 @@ namespace Avalonia.Media
         /// <param name="s">The color string.</param>
         /// <param name="color">The parsed color</param>
         /// <returns>The status of the operation.</returns>
-        public static bool TryParse(string s, out Color color)
+        public static bool TryParse(string? s, out Color color)
         {
             color = default;
 
-            if (s is null)
-            {
-                return false;
-            }
-
-            if (s.Length == 0)
+            if (string.IsNullOrEmpty(s))
             {
                 return false;
             }

src/Avalonia.Base/Media/DrawingContext.cs

@@ -240,7 +240,7 @@ namespace Avalonia.Media
         /// </summary>
         /// <param name="foreground">The foreground brush.</param>
         /// <param name="glyphRun">The glyph run.</param>
-        public void DrawGlyphRun(IBrush foreground, GlyphRun glyphRun)
+        public void DrawGlyphRun(IBrush? foreground, GlyphRun glyphRun)
         {
             _ = glyphRun ?? throw new ArgumentNullException(nameof(glyphRun));
 

src/Avalonia.Base/Media/DrawingGroup.cs

@@ -13,14 +13,14 @@ namespace Avalonia.Media
         public static readonly StyledProperty<double> OpacityProperty =
             AvaloniaProperty.Register<DrawingGroup, double>(nameof(Opacity), 1);
 
-        public static readonly StyledProperty<Transform> TransformProperty =
-            AvaloniaProperty.Register<DrawingGroup, Transform>(nameof(Transform));
+        public static readonly StyledProperty<Transform?> TransformProperty =
+            AvaloniaProperty.Register<DrawingGroup, Transform?>(nameof(Transform));
 
-        public static readonly StyledProperty<Geometry> ClipGeometryProperty =
-            AvaloniaProperty.Register<DrawingGroup, Geometry>(nameof(ClipGeometry));
+        public static readonly StyledProperty<Geometry?> ClipGeometryProperty =
+            AvaloniaProperty.Register<DrawingGroup, Geometry?>(nameof(ClipGeometry));
 
-        public static readonly StyledProperty<IBrush> OpacityMaskProperty =
-            AvaloniaProperty.Register<DrawingGroup, IBrush>(nameof(OpacityMask));
+        public static readonly StyledProperty<IBrush?> OpacityMaskProperty =
+            AvaloniaProperty.Register<DrawingGroup, IBrush?>(nameof(OpacityMask));
 
         public static readonly DirectProperty<DrawingGroup, DrawingCollection> ChildrenProperty =
             AvaloniaProperty.RegisterDirect<DrawingGroup, DrawingCollection>(
@@ -36,19 +36,19 @@ namespace Avalonia.Media
             set => SetValue(OpacityProperty, value);
         }
 
-        public Transform Transform
+        public Transform? Transform
         {
             get => GetValue(TransformProperty);
             set => SetValue(TransformProperty, value);
         }
 
-        public Geometry ClipGeometry
+        public Geometry? ClipGeometry
         {
             get => GetValue(ClipGeometryProperty);
             set => SetValue(ClipGeometryProperty, value);
         }
 
-        public IBrush OpacityMask
+        public IBrush? OpacityMask
         {
             get => GetValue(OpacityMaskProperty);
             set => SetValue(OpacityMaskProperty, value);
@@ -159,7 +159,7 @@ namespace Avalonia.Media
 
             public void DrawGeometry(IBrush? brush, IPen? pen, IGeometryImpl geometry)
             {
-                if (((brush == null) && (pen == null)) || (geometry == null))
+                if ((brush == null) && (pen == null))
                 {
                     return;
                 }
@@ -167,9 +167,9 @@ namespace Avalonia.Media
                 AddNewGeometryDrawing(brush, pen, new PlatformGeometry(geometry));
             }
 
-            public void DrawGlyphRun(IBrush foreground, IRef<IGlyphRunImpl> glyphRun)
+            public void DrawGlyphRun(IBrush? foreground, IRef<IGlyphRunImpl> glyphRun)
             {
-                if (foreground == null || glyphRun == null)
+                if (foreground == null)
                 {
                     return;
                 }
@@ -184,7 +184,7 @@ namespace Avalonia.Media
                 AddDrawing(glyphRunDrawing);
             }
 
-            public void DrawLine(IPen pen, Point p1, Point p2)
+            public void DrawLine(IPen? pen, Point p1, Point p2)
             {
                 if (pen == null)
                 {

src/Avalonia.Base/Media/DrawingImage.cs

@@ -20,8 +20,8 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="Drawing"/> property.
         /// </summary>
-        public static readonly StyledProperty<Drawing> DrawingProperty =
-            AvaloniaProperty.Register<DrawingImage, Drawing>(nameof(Drawing));
+        public static readonly StyledProperty<Drawing?> DrawingProperty =
+            AvaloniaProperty.Register<DrawingImage, Drawing?>(nameof(Drawing));
 
         /// <inheritdoc/>
         public event EventHandler? Invalidated;
@@ -30,7 +30,7 @@ namespace Avalonia.Media
         /// Gets or sets the drawing content.
         /// </summary>
         [Content]
-        public Drawing Drawing
+        public Drawing? Drawing
         {
             get => GetValue(DrawingProperty);
             set => SetValue(DrawingProperty, value);

src/Avalonia.Base/Media/FontFamily.cs

@@ -119,7 +119,7 @@ namespace Avalonia.Media
 
                 case 2:
                     {
-                        var source = segments[0].StartsWith("/")
+                        var source = segments[0].StartsWith("/", StringComparison.Ordinal)
                             ? new Uri(segments[0], UriKind.Relative)
                             : new Uri(segments[0], UriKind.RelativeOrAbsolute);
 
@@ -188,7 +188,7 @@ namespace Avalonia.Media
         {
             unchecked
             {
-                return ((FamilyNames != null ? FamilyNames.GetHashCode() : 0) * 397) ^ (Key != null ? Key.GetHashCode() : 0);
+                return (FamilyNames.GetHashCode() * 397) ^ (Key is not null ? Key.GetHashCode() : 0);
             }
         }
 

src/Avalonia.Base/Media/Fonts/FontFamilyKey.cs

@@ -41,10 +41,7 @@ namespace Avalonia.Media.Fonts
             {
                 var hash = (int)2166136261;
 
-                if (Source != null)
-                {
-                    hash = (hash * 16777619) ^ Source.GetHashCode();
-                }
+                hash = (hash * 16777619) ^ Source.GetHashCode();
 
                 if (BaseUri != null)
                 {

src/Avalonia.Base/Media/FormattedText.cs

@@ -1354,7 +1354,7 @@ namespace Avalonia.Media
                     {
                         var highlightBounds = currentLine.GetTextBounds(x0,x1 - x0);
 
-                        if (highlightBounds != null)
+                        if (highlightBounds.Count > 0)
                         {
                             foreach (var bound in highlightBounds)
                             {
@@ -1365,7 +1365,7 @@ namespace Avalonia.Media
                                     // Convert logical units (which extend leftward from the right edge
                                     // of the paragraph) to physical units.
                                     //
-                                    // Note that since rect is in logical units, rect.Right corresponds to 
+                                    // Note that since rect is in logical units, rect.Right corresponds to
                                     // the visual *left* edge of the rectangle in the RTL case. Specifically,
                                     // is the distance leftward from the right edge of the formatting rectangle
                                     // whose width is the paragraph width passed to FormatLine.
@@ -1384,7 +1384,7 @@ namespace Avalonia.Media
                                 else
                                 {
                                     accumulatedBounds = Geometry.Combine(accumulatedBounds, rectangleGeometry, GeometryCombineMode.Union);
-                                }                                  
+                                }
                             }
                         }
                     }

src/Avalonia.Base/Media/GeometryDrawing.cs

@@ -15,8 +15,8 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="Geometry"/> property.
         /// </summary>
-        public static readonly StyledProperty<Geometry> GeometryProperty =
-            AvaloniaProperty.Register<GeometryDrawing, Geometry>(nameof(Geometry));
+        public static readonly StyledProperty<Geometry?> GeometryProperty =
+            AvaloniaProperty.Register<GeometryDrawing, Geometry?>(nameof(Geometry));
 
         /// <summary>
         /// Defines the <see cref="Brush"/> property.
@@ -34,7 +34,7 @@ namespace Avalonia.Media
         /// Gets or sets the <see cref="Avalonia.Media.Geometry"/> that describes the shape of this <see cref="GeometryDrawing"/>.
         /// </summary>
         [Content]
-        public Geometry Geometry
+        public Geometry? Geometry
         {
             get => GetValue(GeometryProperty);
             set => SetValue(GeometryProperty, value);

src/Avalonia.Base/Media/GlyphRunDrawing.cs

@@ -2,19 +2,19 @@
 {
     public class GlyphRunDrawing : Drawing
     {
-        public static readonly StyledProperty<IBrush> ForegroundProperty =
-            AvaloniaProperty.Register<GlyphRunDrawing, IBrush>(nameof(Foreground));
+        public static readonly StyledProperty<IBrush?> ForegroundProperty =
+            AvaloniaProperty.Register<GlyphRunDrawing, IBrush?>(nameof(Foreground));
 
-        public static readonly StyledProperty<GlyphRun> GlyphRunProperty =
-            AvaloniaProperty.Register<GlyphRunDrawing, GlyphRun>(nameof(GlyphRun));
+        public static readonly StyledProperty<GlyphRun?> GlyphRunProperty =
+            AvaloniaProperty.Register<GlyphRunDrawing, GlyphRun?>(nameof(GlyphRun));
 
-        public IBrush Foreground
+        public IBrush? Foreground
         {
             get => GetValue(ForegroundProperty);
             set => SetValue(ForegroundProperty, value);
         }
 
-        public GlyphRun GlyphRun
+        public GlyphRun? GlyphRun
         {
             get => GetValue(GlyphRunProperty);
             set => SetValue(GlyphRunProperty, value);

src/Avalonia.Base/Media/HslColor.cs

@@ -254,7 +254,7 @@ namespace Avalonia.Media
         /// <param name="s">The HSL color string to parse.</param>
         /// <param name="hslColor">The parsed <see cref="HslColor"/>.</param>
         /// <returns>True if parsing was successful; otherwise, false.</returns>
-        public static bool TryParse(string s, out HslColor hslColor)
+        public static bool TryParse(string? s, out HslColor hslColor)
         {
             bool prefixMatched = false;
 

src/Avalonia.Base/Media/HsvColor.cs

@@ -254,7 +254,7 @@ namespace Avalonia.Media
         /// <param name="s">The HSV color string to parse.</param>
         /// <param name="hsvColor">The parsed <see cref="HsvColor"/>.</param>
         /// <returns>True if parsing was successful; otherwise, false.</returns>
-        public static bool TryParse(string s, out HsvColor hsvColor)
+        public static bool TryParse(string? s, out HsvColor hsvColor)
         {
             bool prefixMatched = false;
 

src/Avalonia.Base/Media/IVisualBrush.cs

@@ -1,5 +1,4 @@
 using Avalonia.Metadata;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Media
 {
@@ -12,6 +11,6 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets the visual to draw.
         /// </summary>
-        Visual Visual { get; }
+        Visual? Visual { get; }
     }
 }

src/Avalonia.Base/Media/Immutable/ImmutableDashStyle.cs

@@ -39,17 +39,8 @@ namespace Avalonia.Media.Immutable
             {
                 return true;
             }
-            else if (other is null)
-            {
-                return false;
-            }
 
-            if (Offset != other.Offset)
-            {
-                return false;
-            }
-
-            return SequenceEqual(Dashes, other.Dashes);
+            return other is not null && Offset == other.Offset && SequenceEqual(_dashes, other.Dashes);
         }
 
         /// <inheritdoc/>
@@ -58,30 +49,27 @@ namespace Avalonia.Media.Immutable
             var hashCode = 717868523;
             hashCode = hashCode * -1521134295 + Offset.GetHashCode();
 
-            if (_dashes != null)
+            foreach (var i in _dashes)
             {
-                foreach (var i in _dashes)
-                {
-                    hashCode = hashCode * -1521134295 + i.GetHashCode();
-                }
+                hashCode = hashCode * -1521134295 + i.GetHashCode();
             }
 
             return hashCode;
         }
 
-        private static bool SequenceEqual(IReadOnlyList<double> left, IReadOnlyList<double>? right)
+        private static bool SequenceEqual(double[] left, IReadOnlyList<double>? right)
         {
             if (ReferenceEquals(left, right))
             {
                 return true;
             }
 
-            if (left == null || right == null || left.Count != right.Count)
+            if (right is null || left.Length != right.Count)
             {
                 return false;
             }
 
-            for (var c = 0; c < left.Count; c++)
+            for (var c = 0; c < left.Length; c++)
             {
                 if (left[c] != right[c])
                 {

src/Avalonia.Base/Media/Immutable/ImmutableVisualBrush.cs

@@ -1,5 +1,4 @@
 using Avalonia.Media.Imaging;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Media.Immutable
 {
@@ -31,11 +30,11 @@ namespace Avalonia.Media.Immutable
             RelativeRect? destinationRect = null,
             double opacity = 1,
             ImmutableTransform? transform = null,
-            RelativePoint transformOrigin = new RelativePoint(),
+            RelativePoint transformOrigin = default,
             RelativeRect? sourceRect = null,
             Stretch stretch = Stretch.Uniform,
             TileMode tileMode = TileMode.None,
-            Imaging.BitmapInterpolationMode bitmapInterpolationMode = Imaging.BitmapInterpolationMode.Default)
+            BitmapInterpolationMode bitmapInterpolationMode = BitmapInterpolationMode.Default)
             : base(
                   alignmentX,
                   alignmentY,
@@ -62,6 +61,6 @@ namespace Avalonia.Media.Immutable
         }
 
         /// <inheritdoc/>
-        public Visual Visual { get; }
+        public Visual? Visual { get; }
     }
 }

src/Avalonia.Base/Media/TextDecoration.cs

@@ -22,8 +22,8 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="Stroke"/> property.
         /// </summary>
-        public static readonly StyledProperty<IBrush> StrokeProperty =
-            AvaloniaProperty.Register<TextDecoration, IBrush>(nameof(Stroke));
+        public static readonly StyledProperty<IBrush?> StrokeProperty =
+            AvaloniaProperty.Register<TextDecoration, IBrush?>(nameof(Stroke));
 
         /// <summary>
         /// Defines the <see cref="StrokeThicknessUnit"/> property.
@@ -34,8 +34,8 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="StrokeDashArray"/> property.
         /// </summary>
-        public static readonly StyledProperty<AvaloniaList<double>> StrokeDashArrayProperty =
-            AvaloniaProperty.Register<TextDecoration, AvaloniaList<double>>(nameof(StrokeDashArray));
+        public static readonly StyledProperty<AvaloniaList<double>?> StrokeDashArrayProperty =
+            AvaloniaProperty.Register<TextDecoration, AvaloniaList<double>?>(nameof(StrokeDashArray));
 
         /// <summary>
         /// Defines the <see cref="StrokeDashOffset"/> property.
@@ -82,7 +82,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets or sets the <see cref="IBrush"/> that specifies how the <see cref="TextDecoration"/> is painted.
         /// </summary>
-        public IBrush Stroke
+        public IBrush? Stroke
         {
             get { return GetValue(StrokeProperty); }
             set { SetValue(StrokeProperty, value); }
@@ -101,7 +101,7 @@ namespace Avalonia.Media
         /// Gets or sets a collection of <see cref="double"/> values that indicate the pattern of dashes and gaps
         /// that is used to draw the <see cref="TextDecoration"/>.
         /// </summary>
-        public AvaloniaList<double> StrokeDashArray
+        public AvaloniaList<double>? StrokeDashArray
         {
             get { return GetValue(StrokeDashArrayProperty); }
             set { SetValue(StrokeDashArrayProperty, value); }
@@ -220,7 +220,7 @@ namespace Avalonia.Media
 
                 var intersections = glyphRun.PlatformImpl.Item.GetIntersections((float)(thickness * 0.5d - offsetY), (float)(thickness * 1.5d - offsetY));
 
-                if (intersections != null && intersections.Count > 0)
+                if (intersections.Count > 0)
                 {
                     var last = baselineOrigin.X;
                     var finalPos = last + glyphRun.Size.Width;

src/Avalonia.Base/Media/VisualBrush.cs

@@ -1,5 +1,4 @@
 using Avalonia.Media.Immutable;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Media
 {
@@ -11,8 +10,8 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="Visual"/> property.
         /// </summary>
-        public static readonly StyledProperty<Visual> VisualProperty =
-            AvaloniaProperty.Register<VisualBrush, Visual>(nameof(Visual));
+        public static readonly StyledProperty<Visual?> VisualProperty =
+            AvaloniaProperty.Register<VisualBrush, Visual?>(nameof(Visual));
 
         static VisualBrush()
         {
@@ -38,7 +37,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets or sets the visual to draw.
         /// </summary>
-        public Visual Visual
+        public Visual? Visual
         {
             get { return GetValue(VisualProperty); }
             set { SetValue(VisualProperty, value); }

src/Avalonia.Base/Platform/IDrawingContextImpl.cs

@@ -49,7 +49,7 @@ namespace Avalonia.Platform
         /// <param name="pen">The stroke pen.</param>
         /// <param name="p1">The first point of the line.</param>
         /// <param name="p2">The second point of the line.</param>
-        void DrawLine(IPen pen, Point p1, Point p2);
+        void DrawLine(IPen? pen, Point p1, Point p2);
 
         /// <summary>
         /// Draws a geometry.
@@ -91,7 +91,7 @@ namespace Avalonia.Platform
         /// </summary>
         /// <param name="foreground">The foreground.</param>
         /// <param name="glyphRun">The glyph run.</param>
-        void DrawGlyphRun(IBrush foreground, IRef<IGlyphRunImpl> glyphRun);
+        void DrawGlyphRun(IBrush? foreground, IRef<IGlyphRunImpl> glyphRun);
 
         /// <summary>
         /// Creates a new <see cref="IRenderTargetBitmapImpl"/> that can be used as a render layer

src/Avalonia.Base/Platform/Internal/AssemblyDescriptor.cs

@@ -19,25 +19,20 @@ internal class AssemblyDescriptor : IAssemblyDescriptor
     public AssemblyDescriptor(Assembly assembly)
     {
         Assembly = assembly;
+        Resources = assembly.GetManifestResourceNames()
+            .ToDictionary(n => n, n => (IAssetDescriptor)new AssemblyResourceDescriptor(assembly, n));
+        Name = assembly.GetName().Name;
 
-        if (assembly != null)
+        using var resources = assembly.GetManifestResourceStream(Constants.AvaloniaResourceName);
+        if (resources != null)
         {
-            Resources = assembly.GetManifestResourceNames()
-                .ToDictionary(n => n, n => (IAssetDescriptor)new AssemblyResourceDescriptor(assembly, n));
-            Name = assembly.GetName().Name;
-            using (var resources = assembly.GetManifestResourceStream(Constants.AvaloniaResourceName))
-            {
-                if (resources != null)
-                {
-                    Resources.Remove(Constants.AvaloniaResourceName);
+            Resources.Remove(Constants.AvaloniaResourceName);
 
-                    var indexLength = new BinaryReader(resources).ReadInt32();
-                    var index = AvaloniaResourcesIndexReaderWriter.ReadIndex(new SlicedStream(resources, 4, indexLength));
-                    var baseOffset = indexLength + 4;
-                    AvaloniaResources = index.ToDictionary(r => GetPathRooted(r), r => (IAssetDescriptor)
-                        new AvaloniaResourceDescriptor(assembly, baseOffset + r.Offset, r.Size));
-                }
-            }
+            var indexLength = new BinaryReader(resources).ReadInt32();
+            var index = AvaloniaResourcesIndexReaderWriter.ReadIndex(new SlicedStream(resources, 4, indexLength));
+            var baseOffset = indexLength + 4;
+            AvaloniaResources = index.ToDictionary(GetPathRooted, r => (IAssetDescriptor)
+                new AvaloniaResourceDescriptor(assembly, baseOffset + r.Offset, r.Size));
         }
     }
 
@@ -45,6 +40,7 @@ internal class AssemblyDescriptor : IAssemblyDescriptor
     public Dictionary<string, IAssetDescriptor>? Resources { get; }
     public Dictionary<string, IAssetDescriptor>? AvaloniaResources { get; }
     public string? Name { get; }
+
     private static string GetPathRooted(AvaloniaResourcesIndexEntry r) =>
         r.Path![0] == '/' ? r.Path : '/' + r.Path;
 }

src/Avalonia.Base/Rendering/Composition/Animations/CompositionAnimation.cs

@@ -23,7 +23,7 @@ namespace Avalonia.Rendering.Composition.Animations
     public abstract class CompositionAnimation : CompositionObject,  ICompositionAnimationBase
     {
         private readonly CompositionPropertySet _propertySet;
-        internal CompositionAnimation(Compositor compositor) : base(compositor, null!)
+        internal CompositionAnimation(Compositor compositor) : base(compositor, null)
         {
             _propertySet = new CompositionPropertySet(compositor);
         }

src/Avalonia.Base/Rendering/Composition/Animations/CompositionAnimationGroup.cs

@@ -19,7 +19,7 @@ namespace Avalonia.Rendering.Composition.Animations
         public void Remove(CompositionAnimation value) => Animations.Remove(value);
         public void RemoveAll() => Animations.Clear();
 
-        public CompositionAnimationGroup(Compositor compositor) : base(compositor, null!)
+        public CompositionAnimationGroup(Compositor compositor) : base(compositor, null)
         {
         }
     }

src/Avalonia.Base/Rendering/Composition/Animations/ImplicitAnimationCollection.cs

@@ -23,7 +23,7 @@ namespace Avalonia.Rendering.Composition.Animations
     {
         private Dictionary<string, ICompositionAnimationBase> _inner = new Dictionary<string, ICompositionAnimationBase>();
         private IDictionary<string, ICompositionAnimationBase> _innerface;
-        internal ImplicitAnimationCollection(Compositor compositor) : base(compositor, null!)
+        internal ImplicitAnimationCollection(Compositor compositor) : base(compositor, null)
         {
             _innerface = _inner;
         }

src/Avalonia.Base/Rendering/Composition/CompositingRenderer.cs

@@ -20,15 +20,17 @@ public class CompositingRenderer : IRendererWithCompositor
 {
     private readonly IRenderRoot _root;
     private readonly Compositor _compositor;
-    CompositionDrawingContext _recorder = new();
-    DrawingContext _recordingContext;
-    private HashSet<Visual> _dirty = new();
-    private HashSet<Visual> _recalculateChildren = new();
+    private readonly CompositionDrawingContext _recorder = new();
+    private readonly DrawingContext _recordingContext;
+    private readonly HashSet<Visual> _dirty = new();
+    private readonly HashSet<Visual> _recalculateChildren = new();
+    private readonly Action _update;
+
     private bool _queuedUpdate;
-    private Action _update;
     private bool _updating;
+    private bool _isDisposed;
 
-    internal CompositionTarget CompositionTarget;
+    internal CompositionTarget CompositionTarget { get; }
     
     /// <summary>
     /// Asks the renderer to only draw frames on the render thread. Makes Paint to wait until frame is rendered.
@@ -38,6 +40,17 @@ public class CompositingRenderer : IRendererWithCompositor
     /// <inheritdoc/>
     public RendererDiagnostics Diagnostics { get; }
 
+    /// <inheritdoc />
+    public Compositor Compositor => _compositor;
+
+    /// <summary>
+    /// Initializes a new instance of <see cref="CompositingRenderer"/>
+    /// </summary>
+    /// <param name="root">The render root using this renderer.</param>
+    /// <param name="compositor">The associated compositors.</param>
+    /// <param name="surfaces">
+    /// A function returning the list of native platform's surfaces that can be consumed by rendering subsystems.
+    /// </param>
     public CompositingRenderer(IRenderRoot root, Compositor compositor, Func<IEnumerable<object>> surfaces)
     {
         _root = root;
@@ -66,7 +79,7 @@ public class CompositingRenderer : IRendererWithCompositor
     /// <inheritdoc/>
     public event EventHandler<SceneInvalidatedEventArgs>? SceneInvalidated;
 
-    void QueueUpdate()
+    private void QueueUpdate()
     {
         if(_queuedUpdate)
             return;
@@ -77,9 +90,11 @@ public class CompositingRenderer : IRendererWithCompositor
     /// <inheritdoc/>
     public void AddDirty(Visual visual)
     {
+        if (_isDisposed)
+            return;
         if (_updating)
             throw new InvalidOperationException("Visual was invalidated during the render pass");
-        _dirty.Add((Visual)visual);
+        _dirty.Add(visual);
         QueueUpdate();
     }
 
@@ -126,9 +141,11 @@ public class CompositingRenderer : IRendererWithCompositor
     /// <inheritdoc/>
     public void RecalculateChildren(Visual visual)
     {
+        if (_isDisposed)
+            return;
         if (_updating)
             throw new InvalidOperationException("Visual was invalidated during the render pass");
-        _recalculateChildren.Add((Visual)visual);
+        _recalculateChildren.Add(visual);
         QueueUpdate();
     }
 
@@ -171,7 +188,7 @@ public class CompositingRenderer : IRendererWithCompositor
             if (sortedChildren != null)
                 for (var c = 0; c < visualChildren.Count; c++)
                 {
-                    if (!ReferenceEquals(compositionChildren[c], ((Visual)sortedChildren[c].visual).CompositionVisual))
+                    if (!ReferenceEquals(compositionChildren[c], sortedChildren[c].visual.CompositionVisual))
                     {
                         mismatch = true;
                         break;
@@ -179,7 +196,7 @@ public class CompositingRenderer : IRendererWithCompositor
                 }
             else
                 for (var c = 0; c < visualChildren.Count; c++)
-                    if (!ReferenceEquals(compositionChildren[c], ((Visual)visualChildren[c]).CompositionVisual))
+                    if (!ReferenceEquals(compositionChildren[c], visualChildren[c].CompositionVisual))
                     {
                         mismatch = true;
                         break;
@@ -201,7 +218,7 @@ public class CompositingRenderer : IRendererWithCompositor
         {
             foreach (var ch in sortedChildren)
             {
-                var compositionChild = ((Visual)ch.visual).CompositionVisual;
+                var compositionChild = ch.visual.CompositionVisual;
                 if (compositionChild != null)
                     compositionChildren.Add(compositionChild);
             }
@@ -210,7 +227,7 @@ public class CompositingRenderer : IRendererWithCompositor
         else
             foreach (var ch in v.GetVisualChildren())
             {
-                var compositionChild = ((Visual)ch).CompositionVisual;
+                var compositionChild = ch.CompositionVisual;
                 if (compositionChild != null)
                     compositionChildren.Add(compositionChild);
             }
@@ -289,13 +306,18 @@ public class CompositingRenderer : IRendererWithCompositor
             _updating = false;
         }
     }
-    
+
+    /// <inheritdoc />
     public void Resized(Size size)
     {
     }
 
+    /// <inheritdoc />
     public void Paint(Rect rect)
     {
+        if (_isDisposed)
+            return;
+
         QueueUpdate();
         CompositionTarget.RequestRedraw();
         if(RenderOnlyOnRenderThread && Compositor.Loop.RunsInBackground)
@@ -304,17 +326,34 @@ public class CompositingRenderer : IRendererWithCompositor
             CompositionTarget.ImmediateUIThreadRender();
     }
 
-    public void Start() => CompositionTarget.IsEnabled = true;
-
-    public void Stop()
+    /// <inheritdoc />
+    public void Start()
     {
-        CompositionTarget.IsEnabled = false;
+        if (_isDisposed)
+            return;
+
+        CompositionTarget.IsEnabled = true;
     }
 
-    public ValueTask<object?> TryGetRenderInterfaceFeature(Type featureType) => Compositor.TryGetRenderInterfaceFeature(featureType);
+    /// <inheritdoc />
+    public void Stop()
+        => CompositionTarget.IsEnabled = false;
+
+    /// <inheritdoc />
+    public ValueTask<object?> TryGetRenderInterfaceFeature(Type featureType)
+        => Compositor.TryGetRenderInterfaceFeature(featureType);
 
+    /// <inheritdoc />
     public void Dispose()
     {
+        if (_isDisposed)
+            return;
+
+        _isDisposed = true;
+        _dirty.Clear();
+        _recalculateChildren.Clear();
+        SceneInvalidated = null;
+
         Stop();
         CompositionTarget.Dispose();
         
@@ -323,9 +362,4 @@ public class CompositingRenderer : IRendererWithCompositor
         if (Compositor.Loop.RunsInBackground)
             _compositor.Commit().Wait();
     }
-
-    /// <summary>
-    /// The associated <see cref="Avalonia.Rendering.Composition.Compositor"/> object
-    /// </summary>
-    public Compositor Compositor => _compositor;
 }

src/Avalonia.Base/Rendering/Composition/CompositionDrawingSurface.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Threading.Tasks;
 using Avalonia.Rendering.Composition.Server;
 using Avalonia.Threading;
@@ -7,7 +6,7 @@ namespace Avalonia.Rendering.Composition;
 
 public class CompositionDrawingSurface : CompositionSurface
 {
-    internal new ServerCompositionDrawingSurface Server => (ServerCompositionDrawingSurface)base.Server;
+    internal new ServerCompositionDrawingSurface Server => (ServerCompositionDrawingSurface)base.Server!;
     internal CompositionDrawingSurface(Compositor compositor) : base(compositor, new ServerCompositionDrawingSurface(compositor.Server))
     {
     }

src/Avalonia.Base/Rendering/Composition/CompositionObject.cs

@@ -22,7 +22,7 @@ namespace Avalonia.Rendering.Composition
         public ImplicitAnimationCollection? ImplicitAnimations { get; set; }
 
         private protected InlineDictionary<CompositionProperty, IAnimationInstance> PendingAnimations;
-        internal CompositionObject(Compositor compositor, ServerObject server)
+        internal CompositionObject(Compositor compositor, ServerObject? server)
         {
             Compositor = compositor;
             Server = server;
@@ -32,7 +32,7 @@ namespace Avalonia.Rendering.Composition
         /// The associated Compositor
         /// </summary>
         public Compositor Compositor { get; }
-        internal ServerObject Server { get; }
+        internal ServerObject? Server { get; }
         public bool IsDisposed { get; private set; }
         private bool _registeredForSerialization;
 

src/Avalonia.Base/Rendering/Composition/CompositionPropertySet.cs

@@ -23,7 +23,7 @@ namespace Avalonia.Rendering.Composition
         private readonly Dictionary<string, ExpressionVariant> _variants = new Dictionary<string, ExpressionVariant>();
         private readonly Dictionary<string, CompositionObject> _objects = new Dictionary<string, CompositionObject>();
         
-        internal CompositionPropertySet(Compositor compositor) : base(compositor, null!)
+        internal CompositionPropertySet(Compositor compositor) : base(compositor, null)
         {
         }
 

src/Avalonia.Base/Rendering/Composition/Drawing/CompositionDrawingContext.cs

@@ -88,8 +88,13 @@ internal class CompositionDrawingContext : IDrawingContextImpl, IDrawingContextW
     }
 
     /// <inheritdoc/>
-    public void DrawLine(IPen pen, Point p1, Point p2)
+    public void DrawLine(IPen? pen, Point p1, Point p2)
     {
+        if (pen is null)
+        {
+            return;
+        }
+
         var next = NextDrawAs<LineNode>();
 
         if (next == null || !next.Item.Equals(Transform, pen, p1, p2))
@@ -159,8 +164,13 @@ internal class CompositionDrawingContext : IDrawingContextImpl, IDrawingContextW
     public object? GetFeature(Type t) => null;
 
     /// <inheritdoc/>
-    public void DrawGlyphRun(IBrush foreground, IRef<IGlyphRunImpl> glyphRun)
+    public void DrawGlyphRun(IBrush? foreground, IRef<IGlyphRunImpl> glyphRun)
     {
+        if (foreground is null)
+        {
+            return;
+        }
+
         var next = NextDrawAs<GlyphRunNode>();
 
         if (next == null || !next.Item.Equals(Transform, foreground, glyphRun))

src/Avalonia.Base/Rendering/Composition/Expressions/Expression.cs

@@ -165,8 +165,6 @@ namespace Avalonia.Rendering.Composition.Expressions
         
         public override ExpressionVariant Evaluate(ref ExpressionEvaluationContext context)
         {
-            if (context.ForeignFunctionInterface == null)
-                return default;
             var args = new List<ExpressionVariant>();
             foreach (var expr in Parameters)
                 args.Add(expr.Evaluate(ref context));

src/Avalonia.Base/Rendering/Composition/Expressions/ExpressionEvaluationContext.cs

@@ -1,5 +1,4 @@
 using System.Collections.Generic;
-using Avalonia.Rendering.Composition.Server;
 
 // Special license applies <see href="https://raw.githubusercontent.com/AvaloniaUI/Avalonia/master/src/Avalonia.Base/Rendering/Composition/License.md">License.md</see>
 

src/Avalonia.Base/Rendering/Composition/Server/DrawingContextProxy.cs

@@ -66,7 +66,7 @@ internal class CompositorDrawingContextProxy : IDrawingContextImpl, IDrawingCont
         _impl.DrawBitmap(source, opacityMask, opacityMaskRect, destRect);
     }
 
-    public void DrawLine(IPen pen, Point p1, Point p2)
+    public void DrawLine(IPen? pen, Point p1, Point p2)
     {
         _impl.DrawLine(pen, p1, p2);
     }
@@ -86,7 +86,7 @@ internal class CompositorDrawingContextProxy : IDrawingContextImpl, IDrawingCont
         _impl.DrawEllipse(brush, pen, rect);
     }
 
-    public void DrawGlyphRun(IBrush foreground, IRef<IGlyphRunImpl> glyphRun)
+    public void DrawGlyphRun(IBrush? foreground, IRef<IGlyphRunImpl> glyphRun)
     {
         _impl.DrawGlyphRun(foreground, glyphRun);
     }

src/Avalonia.Base/Rendering/IRenderRoot.cs

@@ -1,6 +1,4 @@
 using Avalonia.Metadata;
-using Avalonia.Platform;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Rendering
 {

src/Avalonia.Base/Rendering/IRenderer.cs

@@ -90,6 +90,9 @@ namespace Avalonia.Rendering
     
     public interface IRendererWithCompositor : IRenderer
     {
+        /// <summary>
+        /// The associated <see cref="Avalonia.Rendering.Composition.Compositor"/> object
+        /// </summary>
         Compositor Compositor { get; }
     }
 }

src/Avalonia.Base/Rendering/ImmediateRenderer.cs

@@ -48,8 +48,10 @@ namespace Avalonia.Rendering
         /// <inheritdoc/>
         void IVisualBrushRenderer.RenderVisualBrush(IDrawingContextImpl context, IVisualBrush brush)
         {
-            var visual = brush.Visual;
-            Render(new DrawingContext(context), visual, visual.Bounds);
+            if (brush.Visual is { } visual)
+            {
+                Render(new DrawingContext(context), visual, visual.Bounds);
+            }
         }
 
         internal static void Render(Visual visual, DrawingContext context, bool updateTransformedBounds)

src/Avalonia.Base/Rendering/SceneGraph/ExperimentalAcrylicNode.cs

@@ -80,11 +80,8 @@ namespace Avalonia.Rendering.SceneGraph
             {
                 p *= Transform.Invert();
 
-                if (Material != null)
-                {
-                    var rect = Rect.Rect;
-                    return rect.ContainsExclusive(p);
-                }
+                var rect = Rect.Rect;
+                return rect.ContainsExclusive(p);
             }
 
             return false;

src/Avalonia.Base/Utilities/TypeUtilities.cs

@@ -212,7 +212,7 @@ namespace Avalonia.Utilities
 
             var toTypeConverter = TypeDescriptor.GetConverter(toUnderl);
 
-            if (toTypeConverter.CanConvertFrom(from) == true)
+            if (toTypeConverter.CanConvertFrom(from))
             {
                 result = toTypeConverter.ConvertFrom(null, culture, value);
                 return true;
@@ -220,7 +220,7 @@ namespace Avalonia.Utilities
 
             var fromTypeConverter = TypeDescriptor.GetConverter(from);
 
-            if (fromTypeConverter.CanConvertTo(toUnderl) == true)
+            if (fromTypeConverter.CanConvertTo(toUnderl))
             {
                 result = fromTypeConverter.ConvertTo(null, culture, value, toUnderl);
                 return true;
@@ -329,7 +329,7 @@ namespace Avalonia.Utilities
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.ImplicitTypeConvertionRequiresUnreferencedCodeMessage)]
-        public static T ConvertImplicit<T>(object value)
+        public static T ConvertImplicit<T>(object? value)
         {
             if (TryConvertImplicit(typeof(T), value, out var result))
             {
@@ -369,11 +369,6 @@ namespace Avalonia.Utilities
         /// </remarks>
         public static bool IsNumeric(Type type)
         {
-            if (type == null)
-            {
-                return false;
-            }
-
             var underlyingType = Nullable.GetUnderlyingType(type);
 
             if (underlyingType != null)

src/Avalonia.Base/Utilities/WeakEvent.cs

@@ -1,8 +1,4 @@
 using System;
-using System.Collections.Generic;
-using System.Diagnostics.CodeAnalysis;
-using System.Linq;
-using System.Reflection;
 using System.Runtime.CompilerServices;
 using Avalonia.Threading;
 
@@ -15,7 +11,7 @@ public class WeakEvent<TSender, TEventArgs> : WeakEvent where TEventArgs : Event
 {
     private readonly Func<TSender, EventHandler<TEventArgs>, Action> _subscribe;
 
-    readonly ConditionalWeakTable<object, Subscription> _subscriptions = new();
+    private readonly ConditionalWeakTable<object, Subscription> _subscriptions = new();
 
     internal WeakEvent(
         Action<TSender, EventHandler<TEventArgs>> subscribe,
@@ -51,56 +47,6 @@ public class WeakEvent<TSender, TEventArgs> : WeakEvent where TEventArgs : Event
         private readonly WeakEvent<TSender, TEventArgs> _ev;
         private readonly TSender _target;
         private readonly Action _compact;
-
-        struct Entry
-        {
-            WeakReference<IWeakEventSubscriber<TEventArgs>>? _reference;
-            int _hashCode;
-
-            public Entry(IWeakEventSubscriber<TEventArgs> r)
-            {
-                if (r == null)
-                {
-                    _reference = null;
-                    _hashCode = 0;
-                    return;
-                }
-
-                _hashCode = r.GetHashCode();
-                _reference = new WeakReference<IWeakEventSubscriber<TEventArgs>>(r);
-            }
-
-            public bool IsEmpty
-            {
-                get
-                {
-                    if (_reference == null)
-                        return true;
-                    if (_reference.TryGetTarget(out _))
-                        return false;
-                    _reference = null;
-                    return true;
-                }
-            }
-
-            public bool TryGetTarget([MaybeNullWhen(false)]out IWeakEventSubscriber<TEventArgs> target)
-            {
-                if (_reference == null)
-                {
-                    target = null!;
-                    return false;
-                }
-                return _reference.TryGetTarget(out target);
-            }
-
-            public bool Equals(IWeakEventSubscriber<TEventArgs> r)
-            {
-                if (_reference == null || r.GetHashCode() != _hashCode)
-                    return false;
-                return _reference.TryGetTarget(out var target) && target == r;
-            }
-        }
-
         private readonly Action _unsubscribe;
         private readonly WeakHashList<IWeakEventSubscriber<TEventArgs>> _list = new();
         private bool _compactScheduled;
@@ -114,7 +60,7 @@ public class WeakEvent<TSender, TEventArgs> : WeakEvent where TEventArgs : Event
             _unsubscribe = ev._subscribe(target, OnEvent);
         }
 
-        void Destroy()
+        private void Destroy()
         {
             if(_destroyed)
                 return;
@@ -134,15 +80,15 @@ public class WeakEvent<TSender, TEventArgs> : WeakEvent where TEventArgs : Event
                 ScheduleCompact();
         }
 
-        void ScheduleCompact()
+        private void ScheduleCompact()
         {
             if(_compactScheduled || _destroyed)
                 return;
             _compactScheduled = true;
             Dispatcher.UIThread.Post(_compact, DispatcherPriority.Background);
         }
-        
-        void Compact()
+
+        private void Compact()
         {
             if(!_compactScheduled)
                 return;
@@ -152,7 +98,7 @@ public class WeakEvent<TSender, TEventArgs> : WeakEvent where TEventArgs : Event
                 Destroy();
         }
 
-        void OnEvent(object? sender, TEventArgs eventArgs)
+        private void OnEvent(object? sender, TEventArgs eventArgs)
         {
             var alive = _list.GetAlive();
             if(alive == null)
@@ -196,4 +142,4 @@ public class WeakEvent
             return () => unsubscribe(s, handler);
         });
     }
-}
+}

src/Avalonia.Base/Utilities/WeakEventHandlerManager.cs

@@ -60,8 +60,7 @@ namespace Avalonia.Utilities
         private static class SubscriptionTypeStorage<TArgs, TSubscriber>
             where TArgs : EventArgs where TSubscriber : class
         {
-            public static readonly ConditionalWeakTable<object, SubscriptionDic<TArgs, TSubscriber>> Subscribers
-                = new ConditionalWeakTable<object, SubscriptionDic<TArgs, TSubscriber>>();
+            public static readonly ConditionalWeakTable<object, SubscriptionDic<TArgs, TSubscriber>> Subscribers = new();
         }
 
         private class SubscriptionDic<T, TSubscriber> : Dictionary<string, Subscription<T, TSubscriber>>
@@ -69,8 +68,7 @@ namespace Avalonia.Utilities
         {
         }
 
-        private static readonly Dictionary<Type, Dictionary<string, EventInfo>> Accessors
-            = new Dictionary<Type, Dictionary<string, EventInfo>>();
+        private static readonly Dictionary<Type, Dictionary<string, EventInfo>> s_accessors = new();
 
         private class Subscription<T, TSubscriber> where T : EventArgs where TSubscriber : class
         {
@@ -81,18 +79,17 @@ namespace Avalonia.Utilities
             private readonly Delegate _delegate;
 
             private Descriptor[] _data = new Descriptor[2];
-            private int _count = 0;
+            private int _count;
 
-            delegate void CallerDelegate(TSubscriber s, object sender, T args);
-            
-            struct Descriptor
+            private delegate void CallerDelegate(TSubscriber s, object? sender, T args);
+
+            private struct Descriptor
             {
-                public WeakReference<TSubscriber> Subscriber;
-                public CallerDelegate Caller;
+                public WeakReference<TSubscriber>? Subscriber;
+                public CallerDelegate? Caller;
             }
 
-            private static Dictionary<MethodInfo, CallerDelegate> s_Callers =
-                new Dictionary<MethodInfo, CallerDelegate>();
+            private static readonly Dictionary<MethodInfo, CallerDelegate> s_callers = new();
             
             public Subscription(SubscriptionDic<T, TSubscriber> sdic,
                 [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicEvents | DynamicallyAccessedMemberTypes.NonPublicEvents)] Type targetType,
@@ -101,8 +98,8 @@ namespace Avalonia.Utilities
                 _sdic = sdic;
                 _target = target;
                 _eventName = eventName;
-                if (!Accessors.TryGetValue(targetType, out var evDic))
-                    Accessors[targetType] = evDic = new Dictionary<string, EventInfo>();
+                if (!s_accessors.TryGetValue(targetType, out var evDic))
+                    s_accessors[targetType] = evDic = new Dictionary<string, EventInfo>();
 
                 if (evDic.TryGetValue(eventName, out var info))
                 {
@@ -123,12 +120,12 @@ namespace Avalonia.Utilities
 
                 var del = new Action<object, T>(OnEvent);
                 _delegate = del.GetMethodInfo().CreateDelegate(_info.EventHandlerType!, del.Target);
-                _info.AddMethod!.Invoke(target, new[] { _delegate });
+                _info.AddMethod!.Invoke(target, new object?[] { _delegate });
             }
 
-            void Destroy()
+            private void Destroy()
             {
-                _info.RemoveMethod!.Invoke(_target, new[] { _delegate });
+                _info.RemoveMethod!.Invoke(_target, new object?[] { _delegate });
                 _sdic.Remove(_eventName);
             }
 
@@ -146,8 +143,8 @@ namespace Avalonia.Utilities
                 MethodInfo method = s.Method;
 
                 var subscriber = (TSubscriber)s.Target!;
-                if (!s_Callers.TryGetValue(method, out var caller))
-                    s_Callers[method] = caller =
+                if (!s_callers.TryGetValue(method, out var caller))
+                    s_callers[method] = caller =
                         (CallerDelegate)Delegate.CreateDelegate(typeof(CallerDelegate), null, method);
                 _data[_count] = new Descriptor
                 {
@@ -178,7 +175,7 @@ namespace Avalonia.Utilities
                 }
             }
 
-            void Compact(bool preventDestroy = false)
+            private void Compact(bool preventDestroy = false)
             {
                 int empty = -1;
                 for (int c = 0; c < _count; c++)
@@ -206,15 +203,15 @@ namespace Avalonia.Utilities
                     Destroy();
             }
 
-            void OnEvent(object sender, T eventArgs)
+            private void OnEvent(object? sender, T eventArgs)
             {
                 var needCompact = false;
-                for(var c=0; c<_count; c++)
+                for (var c = 0; c < _count; c++)
                 {
-                    var r = _data[c].Subscriber;
+                    var r = _data[c].Subscriber!;
                     if (r.TryGetTarget(out var sub))
                     {
-                        _data[c].Caller(sub, sender, eventArgs);
+                        _data[c].Caller!(sub, sender, eventArgs);
                     }
                     else
                         needCompact = true;

src/Avalonia.Base/Visual.cs

@@ -348,7 +348,7 @@ namespace Avalonia
         /// </summary>
         public void InvalidateVisual()
         {
-            VisualRoot?.Renderer?.AddDirty(this);
+            VisualRoot?.Renderer.AddDirty(this);
         }
 
         /// <summary>
@@ -449,7 +449,7 @@ namespace Avalonia
         protected override void LogicalChildrenCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             base.LogicalChildrenCollectionChanged(sender, e);
-            VisualRoot?.Renderer?.RecalculateChildren(this);
+            VisualRoot?.Renderer.RecalculateChildren(this);
         }
 
         /// <summary>
@@ -477,23 +477,19 @@ namespace Avalonia
             OnAttachedToVisualTree(e);
             AttachedToVisualTree?.Invoke(this, e);
             InvalidateVisual();
-            _visualRoot.Renderer?.RecalculateChildren(_visualParent!);
+            _visualRoot.Renderer.RecalculateChildren(_visualParent!);
 
             if (ZIndex != 0 && VisualParent is Visual parent)
                 parent.HasNonUniformZIndexChildren = true;
 
             var visualChildren = VisualChildren;
+            var visualChildrenCount = visualChildren.Count;
 
-            if (visualChildren != null)
+            for (var i = 0; i < visualChildrenCount; i++)
             {
-                var visualChildrenCount = visualChildren.Count;
-
-                for (var i = 0; i < visualChildrenCount; i++)
+                if (visualChildren[i] is { } child)
                 {
-                    if (visualChildren[i] is Visual child)
-                    {
-                        child.OnAttachedToVisualTreeCore(e);
-                    }
+                    child.OnAttachedToVisualTreeCore(e);
                 }
             }
         }
@@ -540,20 +536,16 @@ namespace Avalonia
             }
 
             DetachedFromVisualTree?.Invoke(this, e);
-            e.Root?.Renderer?.AddDirty(this);
+            e.Root.Renderer.AddDirty(this);
 
             var visualChildren = VisualChildren;
+            var visualChildrenCount = visualChildren.Count;
 
-            if (visualChildren != null)
+            for (var i = 0; i < visualChildrenCount; i++)
             {
-                var visualChildrenCount = visualChildren.Count;
-
-                for (var i = 0; i < visualChildrenCount; i++)
+                if (visualChildren[i] is { } child)
                 {
-                    if (visualChildren[i] is Visual child)
-                    {
-                        child.OnDetachedFromVisualTreeCore(e);
-                    }
+                    child.OnDetachedFromVisualTreeCore(e);
                 }
             }
         }
@@ -659,7 +651,7 @@ namespace Avalonia
                 parentVisual.HasNonUniformZIndexChildren = true;
             
             sender?.InvalidateVisual();
-            parent?.VisualRoot?.Renderer?.RecalculateChildren(parent);
+            parent?.VisualRoot?.Renderer.RecalculateChildren(parent);
         }
 
         /// <summary>

src/Avalonia.Base/VisualTree/VisualExtensions.cs

@@ -46,7 +46,7 @@ namespace Avalonia.VisualTree
             Visual? v = visual ?? throw new ArgumentNullException(nameof(visual));
             var result = 0;
 
-            v = v?.VisualParent;
+            v = v.VisualParent;
 
             while (v != null)
             {
@@ -64,17 +64,13 @@ namespace Avalonia.VisualTree
         /// <param name="visual">The first visual.</param>
         /// <param name="target">The second visual.</param>
         /// <returns>The common ancestor, or null if not found.</returns>
-        public static Visual? FindCommonVisualAncestor(this Visual visual, Visual target)
+        public static Visual? FindCommonVisualAncestor(this Visual? visual, Visual? target)
         {
-            Visual? v = visual ?? throw new ArgumentNullException(nameof(visual));
-
-            if (target is null)
+            if (visual is null || target is null)
             {
                 return null;
             }
 
-            Visual? t = target;
-
             void GoUpwards(ref Visual? node, int count)
             {
                 for (int i = 0; i < count; ++i)
@@ -83,6 +79,9 @@ namespace Avalonia.VisualTree
                 }
             }
 
+            Visual? v = visual;
+            Visual? t = target;
+
             // We want to find lowest node first, then make sure that both nodes are at the same height.
             // By doing that we can sometimes find out that other node is our lowest common ancestor.
             var firstHeight = CalculateDistanceFromRoot(v);
@@ -144,7 +143,7 @@ namespace Avalonia.VisualTree
         /// <param name="visual">The visual.</param>
         /// <param name="includeSelf">If given visual should be included in search.</param>
         /// <returns>First ancestor of given type.</returns>
-        public static T? FindAncestorOfType<T>(this Visual visual, bool includeSelf = false) where T : class
+        public static T? FindAncestorOfType<T>(this Visual? visual, bool includeSelf = false) where T : class
         {
             if (visual is null)
             {
@@ -173,7 +172,7 @@ namespace Avalonia.VisualTree
         /// <param name="visual">The visual.</param>
         /// <param name="includeSelf">If given visual should be included in search.</param>
         /// <returns>First descendant of given type.</returns>
-        public static T? FindDescendantOfType<T>(this Visual visual, bool includeSelf = false) where T : class
+        public static T? FindDescendantOfType<T>(this Visual? visual, bool includeSelf = false) where T : class
         {
             if (visual is null)
             {
@@ -392,7 +391,7 @@ namespace Avalonia.VisualTree
         /// True if <paramref name="visual"/> is an ancestor of <paramref name="target"/>;
         /// otherwise false.
         /// </returns>
-        public static bool IsVisualAncestorOf(this Visual visual, Visual target)
+        public static bool IsVisualAncestorOf(this Visual? visual, Visual? target)
         {
             Visual? current = target?.VisualParent;
 

src/Avalonia.Controls.DataGrid/DataGrid.cs

@@ -3979,7 +3979,7 @@ namespace Avalonia.Controls
                     {
                         if (focusedObject is Control element)
                         {
-                            parent = element.Parent;
+                            parent = element.VisualParent;
                             if (parent != null)
                             {
                                 dataGridWillReceiveRoutedEvent = false;

src/Avalonia.Controls.DataGrid/Utils/TreeHelper.cs

@@ -36,7 +36,7 @@ namespace Avalonia.Controls.Utils
                     {
                         if (child is Control childElement)
                         {
-                            parent = childElement.Parent;
+                            parent = childElement.VisualParent;
                         }
                     }
                     child = parent;

src/Avalonia.Controls/AutoCompleteBox/AutoCompleteBox.cs

@@ -792,7 +792,7 @@ namespace Avalonia.Controls
                     Control? element = focused as Control;
                     if (element != null)
                     {
-                        parent = element.Parent;
+                        parent = element.VisualParent;
                     }
                 }
                 focused = parent;

src/Avalonia.Controls/Button.cs

@@ -394,10 +394,10 @@ namespace Avalonia.Controls
             if (e.GetCurrentPoint(this).Properties.IsLeftButtonPressed)
             {
                 IsPressed = true;
+                e.Handled = true;
 
                 if (ClickMode == ClickMode.Press)
                 {
-                    e.Handled = true;
                     OnClick();
                 }
             }
@@ -411,11 +411,11 @@ namespace Avalonia.Controls
             if (IsPressed && e.InitialPressMouseButton == MouseButton.Left)
             {
                 IsPressed = false;
+                e.Handled = true;
 
                 if (ClickMode == ClickMode.Release &&
                     this.GetVisualsAt(e.GetPosition(this)).Any(c => this == c || this.IsVisualAncestorOf(c)))
                 {
-                    e.Handled = true;
                     OnClick();
                 }
             }

src/Avalonia.Controls/Control.cs

@@ -2,14 +2,12 @@ using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using Avalonia.Automation.Peers;
-using Avalonia.Controls.Documents;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
 using Avalonia.Input;
 using Avalonia.Input.Platform;
 using Avalonia.Interactivity;
 using Avalonia.LogicalTree;
-using Avalonia.Media;
 using Avalonia.Rendering;
 using Avalonia.Styling;
 using Avalonia.Threading;
@@ -211,8 +209,6 @@ namespace Avalonia.Controls
             remove => RemoveHandler(SizeChangedEvent, value);
         }
 
-        public new Control? Parent => (Control?)base.Parent;
-
         /// <inheritdoc/>
         bool IDataTemplateHost.IsDataTemplatesInitialized => _dataTemplates != null;
 

src/Avalonia.Controls/Documents/InlineUIContainer.cs

@@ -64,5 +64,23 @@ namespace Avalonia.Controls.Documents
         internal override void AppendText(StringBuilder stringBuilder)
         {
         }
+
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
+        {
+            base.OnPropertyChanged(change);
+
+            if (change.Property == ChildProperty)
+            {
+                if(change.OldValue is Control oldChild)
+                {
+                    LogicalChildren.Remove(oldChild);
+                }
+
+                if(change.NewValue is Control newChild)
+                {
+                    LogicalChildren.Add(newChild);
+                }
+            }
+        }
     }
 }

src/Avalonia.Controls/ListBox.cs

@@ -104,6 +104,7 @@ namespace Avalonia.Controls
         public void UnselectAll() => Selection.Clear();
 
         protected internal override Control CreateContainerForItemOverride() => new ListBoxItem();
+        protected internal override bool IsItemItsOwnContainerOverride(Control item) => item is ListBoxItem;
 
         /// <inheritdoc/>
         protected override void OnGotFocus(GotFocusEventArgs e)

src/Avalonia.Controls/Platform/DefaultMenuInteractionHandler.cs

@@ -553,7 +553,7 @@ namespace Avalonia.Controls.Platform
             }
         }
 
-        protected static IMenuItem? GetMenuItem(Control? item)
+        protected static IMenuItem? GetMenuItem(StyledElement? item)
         {
             while (true)
             {

src/Avalonia.Controls/Primitives/OverlayPopupHost.cs

@@ -48,7 +48,7 @@ namespace Avalonia.Controls.Primitives
             set { /* Not currently supported in overlay popups */ }
         }
 
-        protected internal override Interactive? InteractiveParent => Parent;
+        protected internal override Interactive? InteractiveParent => (Interactive?)VisualParent;
 
         public void Dispose() => Hide();
 

src/Avalonia.Controls/Primitives/Popup.cs

@@ -723,7 +723,7 @@ namespace Avalonia.Controls.Primitives
 
                     while (e is object && (!e.Focusable || !e.IsEffectivelyEnabled || !e.IsVisible))
                     {
-                        e = e.Parent;
+                        e = e.VisualParent as Control;
                     }
 
                     if (e is object)

src/Avalonia.Controls/Primitives/PopupRoot.cs

@@ -72,12 +72,12 @@ namespace Avalonia.Controls.Primitives
         /// <remarks>
         /// Popup events are passed to their parent window. This facilitates this.
         /// </remarks>
-        protected internal override Interactive? InteractiveParent => Parent;
+        protected internal override Interactive? InteractiveParent => (Interactive?)Parent;
 
         /// <summary>
         /// Gets the control that is hosting the popup root.
         /// </summary>
-        Visual? IHostedVisualTreeRoot.Host => Parent;
+        Visual? IHostedVisualTreeRoot.Host => VisualParent;
 
         /// <summary>
         /// Gets the styling parent of the popup root.

src/Avalonia.Controls/Primitives/ToggleButton.cs

@@ -20,7 +20,7 @@ namespace Avalonia.Controls.Primitives
                 nameof(IsChecked),
                 o => o.IsChecked,
                 (o, v) => o.IsChecked = v,
-                unsetValue: null,
+                unsetValue: false,
                 defaultBindingMode: BindingMode.TwoWay);
 
         /// <summary>

src/Avalonia.Controls/ProgressBar.cs

@@ -231,7 +231,7 @@ namespace Avalonia.Controls
         private void UpdateIndicator()
         {
             // Gets the size of the parent indicator container
-            var barSize = _indicator?.Parent?.Bounds.Size ?? Bounds.Size;
+            var barSize = _indicator?.VisualParent?.Bounds.Size ?? Bounds.Size;
 
             if (_indicator != null)
             {

src/Avalonia.Controls/TextBlock.cs

@@ -673,8 +673,6 @@ namespace Avalonia.Controls
                             controlRun.Control is Control control)
                         {
                             VisualChildren.Remove(control);
-
-                            LogicalChildren.Remove(control);
                         }
                     }
                 }
@@ -693,8 +691,6 @@ namespace Avalonia.Controls
                     {
                         VisualChildren.Add(control);
 
-                        LogicalChildren.Add(control);
-
                         control.Measure(Size.Infinity);
                     }
                 }

src/Avalonia.Controls/TopLevel.cs

@@ -94,7 +94,6 @@ namespace Avalonia.Controls
         private readonly IInputManager? _inputManager;
         private readonly IAccessKeyHandler? _accessKeyHandler;
         private readonly IKeyboardNavigationHandler? _keyboardNavigationHandler;
-        private readonly IPlatformRenderInterface? _renderInterface;
         private readonly IGlobalStyles? _globalStyles;
         private readonly IGlobalThemeVariantProvider? _applicationThemeHost;
         private readonly PointerOverPreProcessor? _pointerOverPreProcessor;
@@ -136,36 +135,21 @@ namespace Avalonia.Controls
         /// </param>
         public TopLevel(ITopLevelImpl impl, IAvaloniaDependencyResolver? dependencyResolver)
         {
-            if (impl == null)
-            {
-                throw new InvalidOperationException(
-                    "Could not create window implementation: maybe no windowing subsystem was initialized?");
-            }
-
-            PlatformImpl = impl;
+            PlatformImpl = impl ?? throw new InvalidOperationException(
+                "Could not create window implementation: maybe no windowing subsystem was initialized?");
 
             _actualTransparencyLevel = PlatformImpl.TransparencyLevel;            
 
-            dependencyResolver = dependencyResolver ?? AvaloniaLocator.Current;
+            dependencyResolver ??= AvaloniaLocator.Current;
 
             _accessKeyHandler = TryGetService<IAccessKeyHandler>(dependencyResolver);
             _inputManager = TryGetService<IInputManager>(dependencyResolver);
             _keyboardNavigationHandler = TryGetService<IKeyboardNavigationHandler>(dependencyResolver);
-            _renderInterface = TryGetService<IPlatformRenderInterface>(dependencyResolver);
             _globalStyles = TryGetService<IGlobalStyles>(dependencyResolver);
             _applicationThemeHost = TryGetService<IGlobalThemeVariantProvider>(dependencyResolver);
 
             Renderer = impl.CreateRenderer(this);
-
-            if (Renderer != null)
-            {
-                Renderer.SceneInvalidated += SceneInvalidated;
-            }
-            else
-            {
-                // Prevent nullable error.
-                Renderer = null!;
-            }
+            Renderer.SceneInvalidated += SceneInvalidated;
 
             impl.SetInputRoot(this);
 
@@ -216,7 +200,7 @@ namespace Avalonia.Controls
 
             if(impl.TryGetFeature<ISystemNavigationManagerImpl>() is {} systemNavigationManager)
             {
-                systemNavigationManager.BackRequested += (s, e) =>
+                systemNavigationManager.BackRequested += (_, e) =>
                 {
                     e.RoutedEvent = BackRequestedEvent;
                     RaiseEvent(e);
@@ -337,7 +321,7 @@ namespace Avalonia.Controls
                 {
                     _layoutManager = CreateLayoutManager();
 
-                    if (_layoutManager is LayoutManager typedLayoutManager && Renderer is not null)
+                    if (_layoutManager is LayoutManager typedLayoutManager)
                     {
                         _layoutDiagnosticBridge = new LayoutDiagnosticBridge(Renderer.Diagnostics, typedLayoutManager);
                         _layoutDiagnosticBridge.SetupBridge();
@@ -356,7 +340,7 @@ namespace Avalonia.Controls
         /// <summary>
         /// Gets the renderer for the window.
         /// </summary>
-        public IRenderer Renderer { get; private set; }
+        public IRenderer Renderer { get; }
 
         internal PixelPoint? LastPointerPosition => _pointerOverPreProcessor?.LastPosition;
         
@@ -450,7 +434,7 @@ namespace Avalonia.Controls
         /// <param name="rect">The dirty area.</param>
         protected virtual void HandlePaint(Rect rect)
         {
-            Renderer?.Paint(rect);
+            Renderer.Paint(rect);
         }
 
         /// <summary>
@@ -468,8 +452,8 @@ namespace Avalonia.Controls
                 _applicationThemeHost.ActualThemeVariantChanged -= GlobalActualThemeVariantChanged;
             }
 
-            Renderer?.Dispose();
-            Renderer = null!;
+            Renderer.SceneInvalidated -= SceneInvalidated;
+            Renderer.Dispose();
 
             _layoutDiagnosticBridge?.Dispose();
             _layoutDiagnosticBridge = null;
@@ -488,7 +472,7 @@ namespace Avalonia.Controls
             
             OnClosed(EventArgs.Empty);
 
-            LayoutManager?.Dispose();
+            LayoutManager.Dispose();
         }
 
         /// <summary>
@@ -503,7 +487,7 @@ namespace Avalonia.Controls
             Width = clientSize.Width;
             Height = clientSize.Height;
             LayoutManager.ExecuteLayoutPass();
-            Renderer?.Resized(clientSize);
+            Renderer.Resized(clientSize);
         }
 
         /// <summary>

src/Avalonia.Controls/Window.cs

@@ -573,7 +573,7 @@ namespace Avalonia.Controls
                     return;
                 }
 
-                Renderer?.Stop();
+                Renderer.Stop();
 
                 if (Owner is Window owner)
                 {
@@ -721,7 +721,7 @@ namespace Avalonia.Controls
                 SetWindowStartupLocation(owner?.PlatformImpl);
 
                 PlatformImpl?.Show(ShowActivated, false);
-                Renderer?.Start();
+                Renderer.Start();
                 OnOpened(EventArgs.Empty);
             }
         }
@@ -798,7 +798,7 @@ namespace Avalonia.Controls
 
                 PlatformImpl?.Show(ShowActivated, true);
 
-                Renderer?.Start();
+                Renderer.Start();
 
                 Observable.FromEventPattern(
                         x => Closed += x,

src/Avalonia.Controls/WindowBase.cs

@@ -129,7 +129,7 @@ namespace Avalonia.Controls
         {
             using (FreezeVisibilityChangeHandling())
             {
-                Renderer?.Stop();
+                Renderer.Stop();
                 PlatformImpl?.Hide();
                 IsVisible = false;
             }
@@ -153,7 +153,7 @@ namespace Avalonia.Controls
                 }
 
                 PlatformImpl?.Show(true, false);
-                Renderer?.Start();
+                Renderer.Start();
                 OnOpened(EventArgs.Empty);
             }
         }
@@ -219,7 +219,7 @@ namespace Avalonia.Controls
             {
                 ClientSize = clientSize;
                 LayoutManager.ExecuteLayoutPass();
-                Renderer?.Resized(clientSize);
+                Renderer.Resized(clientSize);
             }
         }
 

src/Avalonia.Diagnostics/Diagnostics/Controls/Application.cs

@@ -33,7 +33,7 @@ namespace Avalonia.Diagnostics.Controls
             RendererRoot = application.ApplicationLifetime switch
             {
                 Lifetimes.IClassicDesktopStyleApplicationLifetime classic => classic.MainWindow?.Renderer,
-                Lifetimes.ISingleViewApplicationLifetime single => (single.MainView as Visual)?.VisualRoot?.Renderer,
+                Lifetimes.ISingleViewApplicationLifetime single => single.MainView?.VisualRoot?.Renderer,
                 _ => null
             };
 

src/Avalonia.Diagnostics/Diagnostics/ViewModels/EventTreeNode.cs

@@ -115,7 +115,7 @@ namespace Avalonia.Diagnostics.ViewModels
                     var link = _currentEvent.EventChain[linkIndex];
 
                     link.Handled = true;
-                    _currentEvent.HandledBy = link;
+                    _currentEvent.HandledBy ??= link;
                 }
             }
 

src/Avalonia.Diagnostics/Diagnostics/Views/EventsPageView.xaml

@@ -29,6 +29,7 @@
 
     <Style Selector="ListBoxItem.handled" >
       <Setter Property="Background" Value="#d9ffdc" />
+      <Setter Property="Foreground" Value="Black" />
     </Style>
   </UserControl.Styles>
 

src/Avalonia.Headless/HeadlessPlatformRenderInterface.cs

@@ -141,9 +141,7 @@ namespace Avalonia.Headless
             }
 
             public IReadOnlyList<float> GetIntersections(float lowerBound, float upperBound)
-            {
-                return null;
-            }
+                => Array.Empty<float>();
         }
 
         class HeadlessGeometryStub : IGeometryImpl

src/Avalonia.Native/WindowImpl.cs

@@ -119,7 +119,8 @@ namespace Avalonia.Native
             {
                 if(e.Type == RawPointerEventType.LeftButtonDown)
                 {
-                    var visual = (_inputRoot as Window).Renderer.HitTestFirst(e.Position, _inputRoot as Window, x =>
+                    var window = _inputRoot as Window;
+                    var visual = window?.Renderer.HitTestFirst(e.Position, window, x =>
                             {
                                 if (x is IInputElement ie && (!ie.IsHitTestVisible || !ie.IsEffectivelyVisible))
                                 {

src/Skia/Avalonia.Skia/DrawingContextImpl.cs

@@ -208,6 +208,12 @@ namespace Avalonia.Skia
         public void DrawLine(IPen pen, Point p1, Point p2)
         {
             CheckLease();
+
+            if (pen is null)
+            {
+                return;
+            }
+
             using (var paint = CreatePaint(_strokePaint, pen, new Size(Math.Abs(p2.X - p1.X), Math.Abs(p2.Y - p1.Y))))
             {
                 if (paint.Paint is object)
@@ -495,6 +501,12 @@ namespace Avalonia.Skia
         public void DrawGlyphRun(IBrush foreground, IRef<IGlyphRunImpl> glyphRun)
         {
             CheckLease();
+
+            if (foreground is null)
+            {
+                return;
+            }
+
             using (var paintWrapper = CreatePaint(_fillPaint, foreground, glyphRun.Item.Size))
             {
                 var glyphRunImpl = (GlyphRunImpl)glyphRun.Item;

src/Windows/Avalonia.Direct2D1/Media/GlyphRunImpl.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using Avalonia.Platform;
 using SharpDX.DirectWrite;
 
@@ -25,8 +26,6 @@ namespace Avalonia.Direct2D1.Media
         }
 
         public IReadOnlyList<float> GetIntersections(float lowerBound, float upperBound)
-        {
-            return null;
-        }
+            => Array.Empty<float>();
     }
 }

tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.cs

@@ -78,18 +78,6 @@ namespace Avalonia.Base.UnitTests.Data.Core
             GC.KeepAlive(data);
         }
 
-        [Fact]
-        public async Task Should_Coerce_Get_Null_Double_String_To_UnsetValue()
-        {
-            var data = new Class1 { StringValue = null };
-            var target = new BindingExpression(ExpressionObserver.Create(data, o => o.StringValue), typeof(double));
-            var result = await target.Take(1);
-
-            Assert.Equal(AvaloniaProperty.UnsetValue, result);
-
-            GC.KeepAlive(data);
-        }
-
         [Fact]
         public void Should_Convert_Set_String_To_Double()
         {
@@ -249,19 +237,6 @@ namespace Avalonia.Base.UnitTests.Data.Core
             GC.KeepAlive(data);
         }
 
-        [Fact]
-        public void Should_Coerce_Setting_Null_Double_To_Default_Value()
-        {
-            var data = new Class1 { DoubleValue = 5.6 };
-            var target = new BindingExpression(ExpressionObserver.Create(data, o => o.DoubleValue), typeof(string));
-
-            target.OnNext(null);
-
-            Assert.Equal(0, data.DoubleValue);
-
-            GC.KeepAlive(data);
-        }
-
         [Fact]
         public void Should_Coerce_Setting_UnsetValue_Double_To_Default_Value()
         {

tests/Avalonia.Base.UnitTests/Rendering/SceneGraph/DrawOperationTests.cs

@@ -29,7 +29,7 @@ namespace Avalonia.Base.UnitTests.Rendering.SceneGraph
             double height,
             double scaleX,
             double scaleY,
-            double? penThickness,
+            double penThickness,
             double expectedX,
             double expectedY,
             double expectedWidth,
@@ -38,7 +38,7 @@ namespace Avalonia.Base.UnitTests.Rendering.SceneGraph
             var target = new TestRectangleDrawOperation(
                 new Rect(x, y, width, height),
                 Matrix.CreateScale(scaleX, scaleY),
-                penThickness.HasValue ? new Pen(Brushes.Black, penThickness.Value) : null);
+                new Pen(Brushes.Black, penThickness));
             Assert.Equal(new Rect(expectedX, expectedY, expectedWidth, expectedHeight), target.Bounds);
         }
 

tests/Avalonia.Benchmarks/Avalonia.Benchmarks.csproj

@@ -14,7 +14,7 @@
     <ProjectReference Include="..\Avalonia.UnitTests\Avalonia.UnitTests.csproj" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.13.1" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.13.4" />
   </ItemGroup>
   <ItemGroup>
     <Folder Include="Properties\" />

tests/Avalonia.Controls.UnitTests/ButtonTests.cs

@@ -140,10 +140,9 @@ namespace Avalonia.Controls.UnitTests
                 .Returns<Point, Visual, Func<Visual, bool>>((p, r, f) =>
                     r.Bounds.Contains(p) ? new Visual[] { r } : new Visual[0]);
 
-            var target = new TestButton()
+            var target = new TestButton(renderer.Object)
             {
-                Bounds = new Rect(0, 0, 100, 100),
-                Renderer = renderer.Object
+                Bounds = new Rect(0, 0, 100, 100)
             };
 
             bool clicked = false;
@@ -172,10 +171,9 @@ namespace Avalonia.Controls.UnitTests
                 .Returns<Point, Visual, Func<Visual, bool>>((p, r, f) =>
                     r.Bounds.Contains(p) ? new Visual[] { r } : new Visual[0]);
 
-            var target = new TestButton()
+            var target = new TestButton(renderer.Object)
             {
-                Bounds = new Rect(0, 0, 100, 100),
-                Renderer = renderer.Object
+                Bounds = new Rect(0, 0, 100, 100)
             };
 
             bool clicked = false;
@@ -206,11 +204,10 @@ namespace Avalonia.Controls.UnitTests
                     r.Bounds.Contains(p.Transform(r.RenderTransform.Value.Invert())) ?
                     new Visual[] { r } : new Visual[0]);
 
-            var target = new TestButton()
+            var target = new TestButton(renderer.Object)
             {
                 Bounds = new Rect(0, 0, 100, 100),
-                RenderTransform = new TranslateTransform { X = 100, Y = 0 },
-                Renderer = renderer.Object
+                RenderTransform = new TranslateTransform { X = 100, Y = 0 }
             };
 
             //actual bounds of button should  be 100,0,100,100 x -> translated 100 pixels
@@ -386,9 +383,10 @@ namespace Avalonia.Controls.UnitTests
 
         private class TestButton : Button, IRenderRoot
         {
-            public TestButton()
+            public TestButton(IRenderer renderer)
             {
                 IsVisible = true;
+                Renderer = renderer;
             }
 
             public new Rect Bounds
@@ -399,7 +397,7 @@ namespace Avalonia.Controls.UnitTests
 
             public Size ClientSize => throw new NotImplementedException();
 
-            public IRenderer Renderer { get; set; }
+            public IRenderer Renderer { get; }
 
             public double RenderScaling => throw new NotImplementedException();
 

tests/Avalonia.Controls.UnitTests/TopLevelTests.cs

@@ -6,6 +6,7 @@ using Avalonia.Input.Raw;
 using Avalonia.Layout;
 using Avalonia.LogicalTree;
 using Avalonia.Platform;
+using Avalonia.Rendering;
 using Avalonia.Styling;
 using Avalonia.UnitTests;
 using Moq;
@@ -20,7 +21,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 var target = new TestTopLevel(impl.Object);
 
                 Assert.True(((ILogical)target).IsAttachedToLogicalTree);
@@ -32,7 +33,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.Setup(x => x.ClientSize).Returns(new Size(123, 456));
 
                 var target = new TestTopLevel(impl.Object);
@@ -46,7 +47,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.Setup(x => x.ClientSize).Returns(new Size(123, 456));
 
                 var target = new TestTopLevel(impl.Object);
@@ -60,7 +61,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.Setup(x => x.ClientSize).Returns(new Size(123, 456));
 
                 var target = new TestTopLevel(impl.Object);
@@ -76,7 +77,7 @@ namespace Avalonia.Controls.UnitTests
 
             using (UnitTestApplication.Start(services))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 
                 var target = new TestTopLevel(impl.Object, Mock.Of<ILayoutManager>());
 
@@ -91,7 +92,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupProperty(x => x.Resized);
                 impl.SetupGet(x => x.RenderScaling).Returns(1);
 
@@ -117,7 +118,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.Setup(x => x.ClientSize).Returns(new Size(123, 456));
 
                 var target = new TestTopLevel(impl.Object);
@@ -133,7 +134,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
                 impl.Setup(x => x.ClientSize).Returns(new Size(123, 456));
 
@@ -151,7 +152,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
 
                 bool raised = false;
@@ -169,7 +170,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
 
                 var target = new TestTopLevel(impl.Object);
@@ -200,7 +201,7 @@ namespace Avalonia.Controls.UnitTests
 
             using (UnitTestApplication.Start(services))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
 
                 var target = new TestTopLevel(impl.Object);
@@ -222,7 +223,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
                 var target = new TestTopLevel(impl.Object);
                 var child = new TestTopLevel(impl.Object);
@@ -240,7 +241,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
                 var target = new TestTopLevel(impl.Object);
                 var raised = false;
@@ -257,7 +258,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
 
                 var layoutManager = new Mock<ILayoutManager>();
@@ -274,7 +275,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupGet(x => x.RenderScaling).Returns(1);
 
                 var child = new Border { Classes = { "foo" } };
@@ -317,6 +318,14 @@ namespace Avalonia.Controls.UnitTests
                 }.RegisterInNameScope(scope));
         }
 
+        private static Mock<ITopLevelImpl> CreateMockTopLevelImpl()
+        {
+            var renderer = new Mock<ITopLevelImpl>();
+            renderer.Setup(r => r.CreateRenderer(It.IsAny<IRenderRoot>()))
+                .Returns(RendererMocks.CreateRenderer().Object);
+            return renderer;
+        }
+
         private class TestTopLevel : TopLevel
         {
             private readonly ILayoutManager _layoutManager;

tests/Avalonia.Controls.UnitTests/Utils/HotKeyManagerTests.cs

@@ -4,9 +4,7 @@ using Avalonia.Controls.Templates;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
 using Avalonia.Platform;
-using Avalonia.Styling;
 using Avalonia.UnitTests;
-using Moq;
 using Xunit;
 using Factory = System.Func<int, System.Action<object>, Avalonia.Controls.Window, Avalonia.AvaloniaObject>;
 
@@ -20,7 +18,7 @@ namespace Avalonia.Controls.UnitTests.Utils
             using (AvaloniaLocator.EnterScope())
             {
                 AvaloniaLocator.CurrentMutable
-                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock());
+                    .Bind<IWindowingPlatform>().ToConstant(new MockWindowingPlatform());
 
                 var gesture1 = new KeyGesture(Key.A, KeyModifiers.Control);
                 var gesture2 = new KeyGesture(Key.B, KeyModifiers.Control);
@@ -64,7 +62,7 @@ namespace Avalonia.Controls.UnitTests.Utils
                 var commandResult = 0;
                 var expectedParameter = 1;
                 AvaloniaLocator.CurrentMutable
-                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock());
+                    .Bind<IWindowingPlatform>().ToConstant(new MockWindowingPlatform());
 
                 var gesture = new KeyGesture(Key.A, KeyModifiers.Control);
 
@@ -106,7 +104,7 @@ namespace Avalonia.Controls.UnitTests.Utils
                 var target = new KeyboardDevice();
                 var isExecuted = false;
                 AvaloniaLocator.CurrentMutable
-                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock());
+                    .Bind<IWindowingPlatform>().ToConstant(new MockWindowingPlatform());
 
                 var gesture = new KeyGesture(Key.A, KeyModifiers.Control);
 
@@ -146,7 +144,7 @@ namespace Avalonia.Controls.UnitTests.Utils
                 var target = new KeyboardDevice();
                 var clickExecutedCount = 0;
                 AvaloniaLocator.CurrentMutable
-                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock());
+                    .Bind<IWindowingPlatform>().ToConstant(new MockWindowingPlatform());
 
                 var gesture = new KeyGesture(Key.A, KeyModifiers.Control);
 
@@ -199,7 +197,7 @@ namespace Avalonia.Controls.UnitTests.Utils
                 var clickExecutedCount = 0;
                 var commandExecutedCount = 0;
                 AvaloniaLocator.CurrentMutable
-                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock());
+                    .Bind<IWindowingPlatform>().ToConstant(new MockWindowingPlatform());
 
                 var gesture = new KeyGesture(Key.A, KeyModifiers.Control);
 

tests/Avalonia.Controls.UnitTests/WindowBaseTests.cs

@@ -22,7 +22,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<IWindowBaseImpl>();
+                var impl = CreateMockWindowBaseImpl();
                 var target = new TestWindowBase(impl.Object);
 
                 target.Activate();
@@ -36,7 +36,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<IWindowBaseImpl>();
+                var impl = CreateMockWindowBaseImpl();
                 impl.SetupAllProperties();
 
                 bool raised = false;
@@ -55,7 +55,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<IWindowBaseImpl>();
+                var impl = CreateMockWindowBaseImpl();
                 impl.SetupAllProperties();
 
                 bool raised = false;
@@ -241,6 +241,14 @@ namespace Avalonia.Controls.UnitTests
                 }.RegisterInNameScope(scope));
         }
 
+        private static Mock<IWindowBaseImpl> CreateMockWindowBaseImpl()
+        {
+            var renderer = new Mock<IWindowBaseImpl>();
+            renderer.Setup(r => r.CreateRenderer(It.IsAny<IRenderRoot>()))
+                .Returns(RendererMocks.CreateRenderer().Object);
+            return renderer;
+        }
+
         private class TestWindowBase : WindowBase
         {
             public bool IsClosed { get; private set; }

tests/Avalonia.Controls.UnitTests/WindowTests.cs

@@ -15,6 +15,8 @@ namespace Avalonia.Controls.UnitTests
         public void Setting_Title_Should_Set_Impl_Title()
         {
             var windowImpl = new Mock<IWindowImpl>();
+            windowImpl.Setup(r => r.CreateRenderer(It.IsAny<IRenderRoot>()))
+                .Returns(RendererMocks.CreateRenderer().Object);
             var windowingPlatform = new MockWindowingPlatform(() => windowImpl.Object);
 
             using (UnitTestApplication.Start(new TestServices(windowingPlatform: windowingPlatform)))

tests/Avalonia.Controls.UnitTests/WindowingPlatformMock.cs

@@ -1,35 +0,0 @@
-using System;
-using Moq;
-using Avalonia.Platform;
-
-namespace Avalonia.Controls.UnitTests
-{
-    public class WindowingPlatformMock : IWindowingPlatform
-    {
-        private readonly Func<IWindowImpl> _windowImpl;
-        private readonly Func<IPopupImpl> _popupImpl;
-
-        public WindowingPlatformMock(Func<IWindowImpl> windowImpl = null, Func<IPopupImpl> popupImpl = null )
-        {
-            _windowImpl = windowImpl;
-            _popupImpl = popupImpl;
-        }
-
-        public IWindowImpl CreateWindow()
-        {
-            return _windowImpl?.Invoke() ?? Mock.Of<IWindowImpl>(x => x.RenderScaling == 1);
-        }
-
-        public IWindowImpl CreateEmbeddableWindow()
-        {
-            throw new NotImplementedException();
-        }
-
-        public ITrayIconImpl CreateTrayIcon()
-        {
-            return null;
-        }
-
-        public IPopupImpl CreatePopup() => _popupImpl?.Invoke() ?? Mock.Of<IPopupImpl>(x => x.RenderScaling == 1);
-    }
-}

tests/Avalonia.IntegrationTests.Appium/Avalonia.IntegrationTests.Appium.csproj

@@ -10,7 +10,7 @@
   </ItemGroup>
   
   <ItemGroup>
-    <PackageReference Include="Appium.WebDriver" Version="4.3.1" />
+    <PackageReference Include="Appium.WebDriver" Version="4.4.0" />
     <PackageReference Include="Xunit.Extensions.Ordering" Version="1.4.5" />
   </ItemGroup>
 

tests/Avalonia.LeakTests/Avalonia.LeakTests.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net461</TargetFrameworks>
+    <TargetFrameworks>net462</TargetFrameworks>
   </PropertyGroup>
   <Import Project="..\..\build\JetBrains.dotMemoryUnit.props" />
   <Import Project="..\..\build\Moq.props" />

tests/Avalonia.Markup.UnitTests/Data/BindingTests.cs

@@ -648,16 +648,69 @@ namespace Avalonia.Markup.UnitTests.Data
             };
         }
 
+        [Fact]
+        public void Binding_Producing_Default_Value_Should_Result_In_Correct_Priority()
+        {
+            var defaultValue = StyledPropertyClass.NullableDoubleProperty.GetDefaultValue(typeof(StyledPropertyClass));
+
+            var vm = new NullableValuesViewModel() { NullableDouble = defaultValue };
+            var target = new StyledPropertyClass();
+
+            target.Bind(StyledPropertyClass.NullableDoubleProperty, new Binding(nameof(NullableValuesViewModel.NullableDouble)) { Source = vm });
+
+            Assert.Equal(BindingPriority.LocalValue, target.GetDiagnosticInternal(StyledPropertyClass.NullableDoubleProperty).Priority);
+            Assert.Equal(defaultValue, target.GetValue(StyledPropertyClass.NullableDoubleProperty));
+        }
+
+        [Fact]
+        public void Binding_Non_Nullable_ValueType_To_Null_Reverts_To_Default_Value()
+        {
+            var source = new NullableValuesViewModel { NullableDouble = 42 };
+            var target = new StyledPropertyClass();
+            var binding = new Binding(nameof(source.NullableDouble)) { Source = source };
+
+            target.Bind(StyledPropertyClass.DoubleValueProperty, binding);
+            Assert.Equal(42, target.DoubleValue);
+
+            source.NullableDouble = null;
+
+            Assert.Equal(12.3, target.DoubleValue);
+        }
+
+        [Fact]
+        public void Binding_Nullable_ValueType_To_Null_Sets_Value_To_Null()
+        {
+            var source = new NullableValuesViewModel { NullableDouble = 42 };
+            var target = new StyledPropertyClass();
+            var binding = new Binding(nameof(source.NullableDouble)) { Source = source };
+
+            target.Bind(StyledPropertyClass.NullableDoubleProperty, binding);
+            Assert.Equal(42, target.NullableDouble);
+
+            source.NullableDouble = null;
+
+            Assert.Null(target.NullableDouble);
+        }
+
         private class StyledPropertyClass : AvaloniaObject
         {
             public static readonly StyledProperty<double> DoubleValueProperty =
-                        AvaloniaProperty.Register<StyledPropertyClass, double>(nameof(DoubleValue));
+                        AvaloniaProperty.Register<StyledPropertyClass, double>(nameof(DoubleValue), 12.3);
 
             public double DoubleValue
             {
                 get { return GetValue(DoubleValueProperty); }
                 set { SetValue(DoubleValueProperty, value); }
             }
+            
+            public static StyledProperty<double?> NullableDoubleProperty = 
+                AvaloniaProperty.Register<StyledPropertyClass, double?>(nameof(NullableDoubleProperty), -1);
+
+            public double? NullableDouble
+            {
+                get => GetValue(NullableDoubleProperty);
+                set => SetValue(NullableDoubleProperty, value);
+            }
         }
 
         private class DirectPropertyClass : AvaloniaObject
@@ -676,6 +729,21 @@ namespace Avalonia.Markup.UnitTests.Data
             }
         }
 
+        private class NullableValuesViewModel : INotifyPropertyChanged
+        {
+            public event PropertyChangedEventHandler PropertyChanged;
+
+            private double? _nullableDouble;
+            public double? NullableDouble
+            {
+                get => _nullableDouble; set
+                {
+                    _nullableDouble = value;
+                    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(NullableDouble)));
+                }
+            }
+        }
+
         private class TestStackOverflowViewModel : INotifyPropertyChanged
         {
             public int SetterInvokedCount { get; private set; }

tests/Avalonia.UnitTests/MockGlyphRun.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using Avalonia.Media.TextFormatting;
 using Avalonia.Platform;
 
@@ -24,12 +25,9 @@ namespace Avalonia.UnitTests
 
         public void Dispose()
         {
-            
         }
 
         public IReadOnlyList<float> GetIntersections(float lowerBound, float upperBound)
-        {
-            return null;
-        }
+            => Array.Empty<float>();
     }
 }

tests/Avalonia.UnitTests/TestTemplatedRoot.cs

@@ -1,54 +0,0 @@
-using System;
-using Avalonia.Controls;
-using Avalonia.Controls.Presenters;
-using Avalonia.Controls.Templates;
-using Avalonia.Layout;
-using Avalonia.LogicalTree;
-using Avalonia.Platform;
-using Avalonia.Rendering;
-using Avalonia.Styling;
-
-namespace Avalonia.UnitTests
-{
-    public class TestTemplatedRoot : ContentControl, ILayoutRoot, IRenderRoot, ILogicalRoot
-    {
-        private readonly NameScope _nameScope = new NameScope();
-
-        public TestTemplatedRoot()
-        {
-            LayoutManager = new LayoutManager(this);
-            Template = new FuncControlTemplate<TestTemplatedRoot>((x, scope) => new ContentPresenter
-            {
-                Name = "PART_ContentPresenter",
-            }.RegisterInNameScope(scope));
-        }
-
-        public Size ClientSize => new Size(100, 100);
-
-        public Size MaxClientSize => Size.Infinity;
-
-        public double LayoutScaling => 1;
-
-        public ILayoutManager LayoutManager { get; set; }
-
-        public double RenderScaling => 1;
-
-        public IRenderTarget RenderTarget => null;
-
-        public IRenderer Renderer => null;
-
-        public IRenderTarget CreateRenderTarget()
-        {
-            throw new NotImplementedException();
-        }
-
-        public void Invalidate(Rect rect)
-        {
-            throw new NotImplementedException();
-        }
-
-        public Point PointToClient(PixelPoint p) => p.ToPoint(1);
-
-        public PixelPoint PointToScreen(Point p) => PixelPoint.FromPoint(p, 1);
-    }
-}