Merge branch 'master' of https://github.com/AvaloniaUI/Avalonia

readme.md

@@ -31,7 +31,9 @@ Install-Package Avalonia.Desktop
 Examples of UIs built with Avalonia
 ![image](https://user-images.githubusercontent.com/4672627/84707589-5b69a880-af35-11ea-87a6-7ad57a31d314.png)
 
-![image](https://user-images.githubusercontent.com/4672627/84708576-28281900-af37-11ea-8c88-e29dfcfa0558.png)
+![image](https://user-images.githubusercontent.com/4672627/85069644-d8419000-b18a-11ea-8732-be9055bb61fd.PNG)
+
+![image](https://user-images.githubusercontent.com/4672627/85069659-dc6dad80-b18a-11ea-8375-39ef95315b5c.PNG)
 
 ![image](https://user-images.githubusercontent.com/4672627/84708947-c3b98980-af37-11ea-8c9d-503334615bbf.png)
 

samples/ControlCatalog/MainView.xaml

@@ -55,6 +55,7 @@
       <TabItem Header="Pointers (Touch)"><pages:PointersPage/></TabItem>
       <TabItem Header="ProgressBar"><pages:ProgressBarPage/></TabItem>
       <TabItem Header="RadioButton"><pages:RadioButtonPage/></TabItem>
+      <TabItem Header="ScrollViewer"><pages:ScrollViewerPage/></TabItem>
       <TabItem Header="Slider"><pages:SliderPage/></TabItem>
       <TabItem Header="TabControl"><pages:TabControlPage/></TabItem>
       <TabItem Header="TabStrip"><pages:TabStripPage/></TabItem>

samples/ControlCatalog/Pages/ItemsRepeaterPage.xaml

@@ -16,6 +16,8 @@
       <Button Command="{Binding AddItem}">Add Item</Button>
       <Button Command="{Binding RandomizeHeights}">Randomize Heights</Button>
       <Button Command="{Binding ResetItems}">Reset items</Button>
+      <Button x:Name="scrollToLast">Scroll to Last</Button>
+      <Button x:Name="scrollToRandom">Scroll to Random</Button>
     </StackPanel>
     <Border BorderThickness="1" BorderBrush="{DynamicResource ThemeBorderMidBrush}" Margin="0 0 0 16">
       <ScrollViewer Name="scroller"
@@ -24,7 +26,10 @@
         <ItemsRepeater Name="repeater" Background="Transparent" Items="{Binding Items}">
           <ItemsRepeater.ItemTemplate>
             <DataTemplate>
-              <TextBlock Focusable="True" Height="{Binding Height}" Text="{Binding Text}"/>
+              <TextBlock Focusable="True"
+                         Background="{Binding Background}"
+                         Height="{Binding Height}"
+                         Text="{Binding Text}"/>
             </DataTemplate>
           </ItemsRepeater.ItemTemplate>
         </ItemsRepeater>

samples/ControlCatalog/Pages/ItemsRepeaterPage.xaml.cs

@@ -5,23 +5,32 @@ using Avalonia.Controls.Primitives;
 using Avalonia.Input;
 using Avalonia.Layout;
 using Avalonia.Markup.Xaml;
+using Avalonia.VisualTree;
 using ControlCatalog.ViewModels;
 
 namespace ControlCatalog.Pages
 {
     public class ItemsRepeaterPage : UserControl
     {
+        private readonly ItemsRepeaterPageViewModel _viewModel;
         private ItemsRepeater _repeater;
         private ScrollViewer _scroller;
+        private Button _scrollToLast;
+        private Button _scrollToRandom;
+        private Random _random = new Random(0);
 
         public ItemsRepeaterPage()
         {
             this.InitializeComponent();
             _repeater = this.FindControl<ItemsRepeater>("repeater");
             _scroller = this.FindControl<ScrollViewer>("scroller");
+            _scrollToLast = this.FindControl<Button>("scrollToLast");
+            _scrollToRandom = this.FindControl<Button>("scrollToRandom");
             _repeater.PointerPressed += RepeaterClick;
             _repeater.KeyDown += RepeaterOnKeyDown;
-            DataContext = new ItemsRepeaterPageViewModel();
+            _scrollToLast.Click += scrollToLast_Click;
+            _scrollToRandom.Click += scrollToRandom_Click;
+            DataContext = _viewModel = new ItemsRepeaterPageViewModel();
         }
 
         private void InitializeComponent()
@@ -73,18 +82,37 @@ namespace ControlCatalog.Pages
             }
         }
 
+        private void ScrollTo(int index)
+        {
+            System.Diagnostics.Debug.WriteLine("Scroll to " + index);
+            var layoutManager = ((Window)this.GetVisualRoot()).LayoutManager;
+            var element = _repeater.GetOrCreateElement(index);
+            layoutManager.ExecuteLayoutPass();
+            element.BringIntoView();
+        }
+
         private void RepeaterClick(object sender, PointerPressedEventArgs e)
         {
             var item = (e.Source as TextBlock)?.DataContext as ItemsRepeaterPageViewModel.Item;
-            ((ItemsRepeaterPageViewModel)DataContext).SelectedItem = item;
+            _viewModel.SelectedItem = item;
         }
 
         private void RepeaterOnKeyDown(object sender, KeyEventArgs e)
         {
             if (e.Key == Key.F5)
             {
-                ((ItemsRepeaterPageViewModel)DataContext).ResetItems();
+                _viewModel.ResetItems();
             }
         }
+
+        private void scrollToLast_Click(object sender, Avalonia.Interactivity.RoutedEventArgs e)
+        {
+            ScrollTo(_viewModel.Items.Count - 1);
+        }
+
+        private void scrollToRandom_Click(object sender, Avalonia.Interactivity.RoutedEventArgs e)
+        {
+            ScrollTo(_random.Next(_viewModel.Items.Count - 1));
+        }
     }
 }

samples/ControlCatalog/Pages/ScrollViewerPage.xaml

@@ -0,0 +1,35 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="ControlCatalog.Pages.ScrollViewerPage">
+  <StackPanel Orientation="Vertical" Spacing="4">
+    <TextBlock Classes="h1">ScrollViewer</TextBlock>
+    <TextBlock Classes="h2">Allows for horizontal and vertical content scrolling.</TextBlock>
+
+    <Grid ColumnDefinitions="Auto, *">
+      <StackPanel Orientation="Vertical" Spacing="4">
+        <ToggleSwitch IsChecked="{Binding AllowAutoHide}" Content="Allow auto hide" />
+
+        <StackPanel Orientation="Vertical" Spacing="4">
+          <TextBlock Text="Horizontal Scroll" />
+          <ComboBox Items="{Binding AvailableVisibility}" SelectedItem="{Binding HorizontalScrollVisibility}" />
+        </StackPanel>
+
+        <StackPanel Orientation="Vertical" Spacing="4">
+          <TextBlock Text="Vertical Scroll" />
+          <ComboBox Items="{Binding AvailableVisibility}" SelectedItem="{Binding VerticalScrollVisibility}" />
+        </StackPanel>
+      </StackPanel>
+
+      <ScrollViewer x:Name="ScrollViewer"
+                    Grid.Column="1"
+                    Width="400" Height="400"
+                    AllowAutoHide="{Binding AllowAutoHide}"
+                    HorizontalScrollBarVisibility="{Binding HorizontalScrollVisibility}"
+                    VerticalScrollBarVisibility="{Binding VerticalScrollVisibility}">
+        <Image Width="800" Height="800" Stretch="UniformToFill"
+               Source="/Assets/delicate-arch-896885_640.jpg" />
+      </ScrollViewer>
+    </Grid>
+
+  </StackPanel>
+</UserControl>

samples/ControlCatalog/Pages/ScrollViewerPage.xaml.cs

@@ -0,0 +1,65 @@
+using System.Collections.Generic;
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Markup.Xaml;
+using ReactiveUI;
+
+namespace ControlCatalog.Pages
+{
+    public class ScrollViewerPageViewModel : ReactiveObject
+    {
+        private bool _allowAutoHide;
+        private ScrollBarVisibility _horizontalScrollVisibility;
+        private ScrollBarVisibility _verticalScrollVisibility;
+
+        public ScrollViewerPageViewModel()
+        {
+            AvailableVisibility = new List<ScrollBarVisibility>
+            {
+                ScrollBarVisibility.Auto,
+                ScrollBarVisibility.Visible,
+                ScrollBarVisibility.Hidden,
+                ScrollBarVisibility.Disabled,
+            };
+
+            HorizontalScrollVisibility = ScrollBarVisibility.Auto;
+            VerticalScrollVisibility = ScrollBarVisibility.Auto;
+            AllowAutoHide = true;
+        }
+
+        public bool AllowAutoHide
+        {
+            get => _allowAutoHide;
+            set => this.RaiseAndSetIfChanged(ref _allowAutoHide, value);
+        }
+
+        public ScrollBarVisibility HorizontalScrollVisibility
+        {
+            get => _horizontalScrollVisibility;
+            set => this.RaiseAndSetIfChanged(ref _horizontalScrollVisibility, value);
+        }
+
+        public ScrollBarVisibility VerticalScrollVisibility
+        {
+            get => _verticalScrollVisibility;
+            set => this.RaiseAndSetIfChanged(ref _verticalScrollVisibility, value);
+        }
+
+        public List<ScrollBarVisibility> AvailableVisibility { get; }
+    }
+
+    public class ScrollViewerPage : UserControl
+    {
+        public ScrollViewerPage()
+        {
+            InitializeComponent();
+
+            DataContext = new ScrollViewerPageViewModel();
+        }
+
+        private void InitializeComponent()
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
+    }
+}

samples/ControlCatalog/ViewModels/ItemsRepeaterPageViewModel.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.ObjectModel;
 using System.Linq;
+using Avalonia.Media;
 using ReactiveUI;
 
 namespace ControlCatalog.ViewModels
@@ -27,7 +28,7 @@ namespace ControlCatalog.ViewModels
         public void AddItem()
         {
             var index = SelectedItem != null ? Items.IndexOf(SelectedItem) : -1;
-            Items.Insert(index + 1, new Item { Text = $"New Item {_newItemIndex++}" });
+            Items.Insert(index + 1, new Item(index + 1) { Text = $"New Item {_newItemIndex++}" });
         }
 
         public void RandomizeHeights()
@@ -52,7 +53,7 @@ namespace ControlCatalog.ViewModels
             _newGenerationIndex++;
 
             return new ObservableCollection<Item>(
-                Enumerable.Range(1, 100000).Select(i => new Item
+                Enumerable.Range(1, 100000).Select(i => new Item(i)
                 {
                     Text = $"Item {i.ToString()} {suffix}"
                 }));
@@ -61,6 +62,12 @@ namespace ControlCatalog.ViewModels
         public class Item : ReactiveObject
         {
             private double _height = double.NaN;
+            private int _index;
+
+            public Item(int index)
+            {
+                _index = index;
+            }
 
             public string Text { get; set; }
             
@@ -69,6 +76,8 @@ namespace ControlCatalog.ViewModels
                 get => _height;
                 set => this.RaiseAndSetIfChanged(ref _height, value);
             }
+
+            public IBrush Background => ((_index % 2) == 0) ? Brushes.Yellow : Brushes.Wheat;
         }
     }
 }

src/Avalonia.Base/Utilities/MathUtilities.cs

@@ -206,39 +206,6 @@ namespace Avalonia.Utilities
             }
         }
 
-        /// <summary>
-        /// Calculates the value to be used for layout rounding at high DPI.
-        /// </summary>
-        /// <param name="value">Input value to be rounded.</param>
-        /// <param name="dpiScale">Ratio of screen's DPI to layout DPI</param>
-        /// <returns>Adjusted value that will produce layout rounding on screen at high dpi.</returns>
-        /// <remarks>This is a layout helper method. It takes DPI into account and also does not return
-        /// the rounded value if it is unacceptable for layout, e.g. Infinity or NaN. It's a helper associated with
-        /// UseLayoutRounding  property and should not be used as a general rounding utility.</remarks>
-        public static double RoundLayoutValue(double value, double dpiScale)
-        {
-            double newValue;
-
-            // If DPI == 1, don't use DPI-aware rounding.
-            if (!MathUtilities.IsOne(dpiScale))
-            {
-                newValue = Math.Round(value * dpiScale) / dpiScale;
-                // If rounding produces a value unacceptable to layout (NaN, Infinity or MaxValue), use the original value.
-                if (double.IsNaN(newValue) ||
-                    double.IsInfinity(newValue) ||
-                    MathUtilities.AreClose(newValue, double.MaxValue))
-                {
-                    newValue = value;
-                }
-            }
-            else
-            {
-                newValue = Math.Round(value);
-            }
-
-            return newValue;
-        }
-
         /// <summary>
         /// Clamps a value between a minimum and maximum value.
         /// </summary>

src/Avalonia.Controls/Grid.cs

@@ -8,10 +8,8 @@ using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.Diagnostics;
-using System.Linq;
 using System.Threading;
-using Avalonia;
-using Avalonia.Collections;
+using Avalonia.Layout;
 using Avalonia.Media;
 using Avalonia.Utilities;
 using Avalonia.VisualTree;
@@ -2103,7 +2101,7 @@ namespace Avalonia.Controls
                 for (int i = 0; i < definitions.Count; ++i)
                 {
                     DefinitionBase def = definitions[i];
-                    double roundedSize = MathUtilities.RoundLayoutValue(def.SizeCache, dpi);
+                    double roundedSize = LayoutHelper.RoundLayoutValue(def.SizeCache, dpi);
                     roundingErrors[i] = (roundedSize - def.SizeCache);
                     def.SizeCache = roundedSize;
                     roundedTakenSize += roundedSize;

src/Avalonia.Controls/IScrollAnchorProvider.cs

@@ -1,9 +1,29 @@
 namespace Avalonia.Controls
 {
+    /// <summary>
+    /// Specifies a contract for a scrolling control that supports scroll anchoring.
+    /// </summary>
     public interface IScrollAnchorProvider
     {
+        /// <summary>
+        /// The currently chosen anchor element to use for scroll anchoring.
+        /// </summary>
         IControl CurrentAnchor { get; }
+
+        /// <summary>
+        /// Registers a control as a potential scroll anchor candidate.
+        /// </summary>
+        /// <param name="element">
+        /// A control within the subtree of the <see cref="IScrollAnchorProvider"/>.
+        /// </param>
         void RegisterAnchorCandidate(IControl element);
+
+        /// <summary>
+        /// Unregisters a control as a potential scroll anchor candidate.
+        /// </summary>
+        /// <param name="element">
+        /// A control within the subtree of the <see cref="IScrollAnchorProvider"/>.
+        /// </param>
         void UnregisterAnchorCandidate(IControl element);
     }
 }

src/Avalonia.Controls/Presenters/ScrollContentPresenter.cs

@@ -3,10 +3,8 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Reactive.Disposables;
 using System.Reactive.Linq;
-using System.Runtime.InteropServices.ComTypes;
 using Avalonia.Controls.Primitives;
 using Avalonia.Input;
-using Avalonia.LogicalTree;
 using Avalonia.VisualTree;
 
 namespace Avalonia.Controls.Presenters
@@ -14,7 +12,7 @@ namespace Avalonia.Controls.Presenters
     /// <summary>
     /// Presents a scrolling view of content inside a <see cref="ScrollViewer"/>.
     /// </summary>
-    public class ScrollContentPresenter : ContentPresenter, IPresenter, IScrollable
+    public class ScrollContentPresenter : ContentPresenter, IPresenter, IScrollable, IScrollAnchorProvider
     {
         /// <summary>
         /// Defines the <see cref="CanHorizontallyScroll"/> property.
@@ -58,13 +56,19 @@ namespace Avalonia.Controls.Presenters
                 o => o.Viewport,
                 (o, v) => o.Viewport = v);
 
+        // Arbitrary chosen value, probably need to ask ILogicalScrollable
+        private const int LogicalScrollItemSize = 50;
+
         private bool _canHorizontallyScroll;
         private bool _canVerticallyScroll;
+        private bool _arranging;
         private Size _extent;
         private Vector _offset;
         private IDisposable _logicalScrollSubscription;
         private Size _viewport;
         private Dictionary<int, Vector> _activeLogicalGestureScrolls;
+        private List<IControl> _anchorCandidates;
+        private (IControl control, Rect bounds) _anchor;
 
         /// <summary>
         /// Initializes static members of the <see cref="ScrollContentPresenter"/> class.
@@ -73,7 +77,6 @@ namespace Avalonia.Controls.Presenters
         {
             ClipToBoundsProperty.OverrideDefaultValue(typeof(ScrollContentPresenter), true);
             ChildProperty.Changed.AddClassHandler<ScrollContentPresenter>((x, e) => x.ChildChanged(e));
-            AffectsArrange<ScrollContentPresenter>(OffsetProperty);
         }
 
         /// <summary>
@@ -87,6 +90,8 @@ namespace Avalonia.Controls.Presenters
             this.GetObservable(ChildProperty).Subscribe(UpdateScrollableSubscription);
         }
 
+        internal event EventHandler<VectorEventArgs> PreArrange;
+
         /// <summary>
         /// Gets or sets a value indicating whether the content can be scrolled horizontally.
         /// </summary>
@@ -120,7 +125,7 @@ namespace Avalonia.Controls.Presenters
         public Vector Offset
         {
             get { return _offset; }
-            set { SetAndRaise(OffsetProperty, ref _offset, value); }
+            set { SetAndRaise(OffsetProperty, ref _offset, ScrollViewer.CoerceOffset(Extent, Viewport, value)); }
         }
 
         /// <summary>
@@ -132,6 +137,9 @@ namespace Avalonia.Controls.Presenters
             private set { SetAndRaise(ViewportProperty, ref _viewport, value); }
         }
 
+        /// <inheritdoc/>
+        IControl IScrollAnchorProvider.CurrentAnchor => _anchor.control;
+
         /// <summary>
         /// Attempts to bring a portion of the target visual into view by scrolling the content.
         /// </summary>
@@ -196,6 +204,30 @@ namespace Avalonia.Controls.Presenters
             return result;
         }
 
+        /// <inheritdoc/>
+        void IScrollAnchorProvider.RegisterAnchorCandidate(IControl element)
+        {
+            if (!this.IsVisualAncestorOf(element))
+            {
+                throw new InvalidOperationException(
+                    "An anchor control must be a visual descendent of the ScrollContentPresenter.");
+            }
+
+            _anchorCandidates ??= new List<IControl>();
+            _anchorCandidates.Add(element);
+        }
+
+        /// <inheritdoc/>
+        void IScrollAnchorProvider.UnregisterAnchorCandidate(IControl element)
+        {
+            _anchorCandidates?.Remove(element);
+
+            if (_anchor.control == element)
+            {
+                _anchor = default;
+            }
+        }
+
         /// <inheritdoc/>
         protected override Size MeasureOverride(Size availableSize)
         {
@@ -215,22 +247,85 @@ namespace Avalonia.Controls.Presenters
         /// <inheritdoc/>
         protected override Size ArrangeOverride(Size finalSize)
         {
+            PreArrange?.Invoke(this, new VectorEventArgs
+            {
+                Vector = new Vector(finalSize.Width, finalSize.Height),
+            });
+
             if (_logicalScrollSubscription != null || Child == null)
             {
                 return base.ArrangeOverride(finalSize);
             }
 
+            try
+            {
+                _arranging = true;
+                return ArrangeWithAnchoring(finalSize);
+            }
+            finally
+            {
+                _arranging = false;
+            }
+        }
+
+        private Size ArrangeWithAnchoring(Size finalSize)
+        {
             var size = new Size(
                 CanHorizontallyScroll ? Math.Max(Child.DesiredSize.Width, finalSize.Width) : finalSize.Width,
                 CanVerticallyScroll ? Math.Max(Child.DesiredSize.Height, finalSize.Height) : finalSize.Height);
+
+            Vector TrackAnchor()
+            {
+                // If we have an anchor and its position relative to Child has changed during the
+                // arrange then that change wasn't just due to scrolling (as scrolling doesn't adjust
+                // relative positions within Child).
+                if (_anchor.control != null &&
+                    TranslateBounds(_anchor.control, Child, out var updatedBounds) &&
+                    updatedBounds.Position != _anchor.bounds.Position)
+                {
+                    var offset = updatedBounds.Position - _anchor.bounds.Position;
+                    return offset;
+                }
+
+                return default;
+            }
+
+            // Calculate the new anchor element.
+            _anchor = CalculateCurrentAnchor();
+
+            // Do the arrange.
             ArrangeOverrideImpl(size, -Offset);
+
+            // If the anchor moved during the arrange, we need to adjust the offset and do another arrange.
+            var anchorShift = TrackAnchor();
+
+            if (anchorShift != default)
+            {
+                var newOffset = Offset + anchorShift;
+                var newExtent = Extent;
+                var maxOffset = new Vector(Extent.Width - Viewport.Width, Extent.Height - Viewport.Height);
+
+                if (newOffset.X > maxOffset.X)
+                {
+                    newExtent = newExtent.WithWidth(newOffset.X + Viewport.Width);
+                }
+
+                if (newOffset.Y > maxOffset.Y)
+                {
+                    newExtent = newExtent.WithHeight(newOffset.Y + Viewport.Height);
+                }
+
+                Extent = newExtent;
+                Offset = newOffset;
+                ArrangeOverrideImpl(size, -Offset);
+            }
+
             Viewport = finalSize;
             Extent = Child.Bounds.Size.Inflate(Child.Margin);
+
             return finalSize;
         }
 
-        // Arbitrary chosen value, probably need to ask ILogicalScrollable
-        private const int LogicalScrollItemSize = 50;
         private void OnScrollGesture(object sender, ScrollGestureEventArgs e)
         {
             if (Extent.Height > Viewport.Height || Extent.Width > Viewport.Width)
@@ -327,6 +422,16 @@ namespace Avalonia.Controls.Presenters
             }
         }
 
+        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        {
+            if (change.Property == OffsetProperty && !_arranging)
+            {
+                InvalidateArrange();
+            }
+
+            base.OnPropertyChanged(change);
+        }
+
         private void BringIntoViewRequested(object sender, RequestBringIntoViewEventArgs e)
         {
             e.Handled = BringDescendantIntoView(e.TargetObject, e.TargetRect);
@@ -390,5 +495,84 @@ namespace Avalonia.Controls.Presenters
                 Offset = scrollable.Offset;
             }
         }
+
+        private (IControl, Rect) CalculateCurrentAnchor()
+        {
+            if (_anchorCandidates == null)
+            {
+                return default;
+            }
+
+            var bestCandidate = default(IControl);
+            var bestCandidateDistance = double.MaxValue;
+
+            // Find the anchor candidate that is scrolled closest to the top-left of this
+            // ScrollContentPresenter.
+            foreach (var element in _anchorCandidates)
+            {
+                if (element.IsVisible && GetViewportBounds(element, out var bounds))
+                {
+                    var distance = (Vector)bounds.Position;
+                    var candidateDistance = Math.Abs(distance.Length);
+
+                    if (candidateDistance < bestCandidateDistance)
+                    {
+                        bestCandidate = element;
+                        bestCandidateDistance = candidateDistance;
+                    }
+                }
+            }
+
+            if (bestCandidate != null)
+            {
+                // We have a candidate, calculate its bounds relative to Child. Because these
+                // bounds aren't relative to the ScrollContentPresenter itself, if they change
+                // then we know it wasn't just due to scrolling.
+                var unscrolledBounds = TranslateBounds(bestCandidate, Child);
+                return (bestCandidate, unscrolledBounds);
+            }
+
+            return default;
+        }
+
+        private bool GetViewportBounds(IControl element, out Rect bounds)
+        {
+            if (TranslateBounds(element, Child, out var childBounds))
+            {
+                // We want the bounds relative to the new Offset, regardless of whether the child
+                // control has actually been arranged to this offset yet, so translate first to the
+                // child control and then apply Offset rather than translating directly to this
+                // control.
+                var thisBounds = new Rect(Bounds.Size);
+                bounds = new Rect(childBounds.Position - Offset, childBounds.Size);
+                return bounds.Intersects(thisBounds);
+            }
+
+            bounds = default;
+            return false;
+        }
+
+        private Rect TranslateBounds(IControl control, IControl to)
+        {
+            if (TranslateBounds(control, to, out var bounds))
+            {
+                return bounds;
+            }
+
+            throw new InvalidOperationException("The control's bounds could not be translated to the requested control.");
+        }
+
+        private bool TranslateBounds(IControl control, IControl to, out Rect bounds)
+        {
+            if (!control.IsVisible)
+            {
+                bounds = default;
+                return false;
+            }
+
+            var p = control.TranslatePoint(default, to);
+            bounds = p.HasValue ? new Rect(p.Value, control.Bounds.Size) : default;
+            return p.HasValue;
+        }
     }
 }

src/Avalonia.Controls/Primitives/HeaderedContentControl.cs

@@ -1,8 +1,9 @@
-using Avalonia.Controls.Mixins;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Templates;
 using Avalonia.LogicalTree;
 
+#nullable enable
+
 namespace Avalonia.Controls.Primitives
 {
     /// <summary>
@@ -13,36 +14,36 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Defines the <see cref="Header"/> property.
         /// </summary>
-        public static readonly StyledProperty<object> HeaderProperty =
-            AvaloniaProperty.Register<HeaderedContentControl, object>(nameof(Header));
+        public static readonly StyledProperty<object?> HeaderProperty =
+            AvaloniaProperty.Register<HeaderedContentControl, object?>(nameof(Header));
 
         /// <summary>
         /// Defines the <see cref="HeaderTemplate"/> property.
         /// </summary>
-        public static readonly StyledProperty<IDataTemplate> HeaderTemplateProperty =
-            AvaloniaProperty.Register<HeaderedContentControl, IDataTemplate>(nameof(HeaderTemplate));
+        public static readonly StyledProperty<IDataTemplate?> HeaderTemplateProperty =
+            AvaloniaProperty.Register<HeaderedContentControl, IDataTemplate?>(nameof(HeaderTemplate));
 
         /// <summary>
         /// Initializes static members of the <see cref="ContentControl"/> class.
         /// </summary>
         static HeaderedContentControl()
         {
-            ContentProperty.Changed.AddClassHandler<HeaderedContentControl>((x, e) => x.HeaderChanged(e));
+            HeaderProperty.Changed.AddClassHandler<HeaderedContentControl>((x, e) => x.HeaderChanged(e));
         }
 
         /// <summary>
         /// Gets or sets the header content.
         /// </summary>
-        public object Header
+        public object? Header
         {
-            get { return GetValue(HeaderProperty); }
-            set { SetValue(HeaderProperty, value); }
+            get => GetValue(HeaderProperty);
+            set => SetValue(HeaderProperty, value);
         }
 
         /// <summary>
         /// Gets the header presenter from the control's template.
         /// </summary>
-        public IContentPresenter HeaderPresenter
+        public IContentPresenter? HeaderPresenter
         {
             get;
             private set;
@@ -51,10 +52,10 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Gets or sets the data template used to display the header content of the control.
         /// </summary>
-        public IDataTemplate HeaderTemplate
+        public IDataTemplate? HeaderTemplate
         {
-            get { return GetValue(HeaderTemplateProperty); }
-            set { SetValue(HeaderTemplateProperty, value); }
+            get => GetValue(HeaderTemplateProperty);
+            set => SetValue(HeaderTemplateProperty, value);
         }
 
         /// <inheritdoc/>

src/Avalonia.Controls/Primitives/ScrollBar.cs

@@ -3,6 +3,7 @@ using Avalonia.Data;
 using Avalonia.Interactivity;
 using Avalonia.Input;
 using Avalonia.Layout;
+using Avalonia.Threading;
 
 namespace Avalonia.Controls.Primitives
 {
@@ -40,10 +41,26 @@ namespace Avalonia.Controls.Primitives
         public static readonly StyledProperty<Orientation> OrientationProperty =
             AvaloniaProperty.Register<ScrollBar, Orientation>(nameof(Orientation), Orientation.Vertical);
 
+        /// <summary>
+        /// Defines the <see cref="IsExpandedProperty"/> property.
+        /// </summary>
+        public static readonly DirectProperty<ScrollBar, bool> IsExpandedProperty =
+            AvaloniaProperty.RegisterDirect<ScrollBar, bool>(
+                nameof(IsExpanded),
+                o => o.IsExpanded);
+
+        /// <summary>
+        /// Defines the <see cref="AllowAutoHide"/> property.
+        /// </summary>
+        public static readonly StyledProperty<bool> AllowAutoHideProperty =
+            AvaloniaProperty.Register<ScrollBar, bool>(nameof(AllowAutoHide), true);
+
         private Button _lineUpButton;
         private Button _lineDownButton;
         private Button _pageUpButton;
         private Button _pageDownButton;
+        private DispatcherTimer _timer;
+        private bool _isExpanded;
 
         /// <summary>
         /// Initializes static members of the <see cref="ScrollBar"/> class. 
@@ -90,6 +107,24 @@ namespace Avalonia.Controls.Primitives
             set { SetValue(OrientationProperty, value); }
         }
 
+        /// <summary>
+        /// Gets a value that indicates whether the scrollbar is expanded.
+        /// </summary>
+        public bool IsExpanded
+        {
+            get => _isExpanded;
+            private set => SetAndRaise(IsExpandedProperty, ref _isExpanded, value);
+        }
+
+        /// <summary>
+        /// Gets a value that indicates whether the scrollbar can hide itself when user is not interacting with it.
+        /// </summary>
+        public bool AllowAutoHide
+        {
+            get => GetValue(AllowAutoHideProperty);
+            set => SetValue(AllowAutoHideProperty, value);
+        }
+
         public event EventHandler<ScrollEventArgs> Scroll;
 
         /// <summary>
@@ -131,6 +166,10 @@ namespace Avalonia.Controls.Primitives
             {
                 UpdatePseudoClasses(change.NewValue.GetValueOrDefault<Orientation>());
             }
+            else if (change.Property == AllowAutoHideProperty)
+            {
+                UpdateIsExpandedState();
+            }
             else
             {
                 if (change.Property == MinimumProperty ||
@@ -143,6 +182,26 @@ namespace Avalonia.Controls.Primitives
             }
         }
 
+        protected override void OnPointerEnter(PointerEventArgs e)
+        {
+            base.OnPointerEnter(e);
+
+            if (AllowAutoHide)
+            {
+                ExpandAfterDelay();
+            }
+        }
+
+        protected override void OnPointerLeave(PointerEventArgs e)
+        {
+            base.OnPointerLeave(e);
+
+            if (AllowAutoHide)
+            {
+                CollapseAfterDelay();
+            }
+        }
+
         protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
         {
             if (_lineUpButton != null)
@@ -170,8 +229,6 @@ namespace Avalonia.Controls.Primitives
             _pageUpButton = e.NameScope.Find<Button>("PART_PageUpButton");
             _pageDownButton = e.NameScope.Find<Button>("PART_PageDownButton");
 
-
-
             if (_lineUpButton != null)
             {
                 _lineUpButton.Click += LineUpClick;
@@ -193,6 +250,68 @@ namespace Avalonia.Controls.Primitives
             }
         }
 
+        private void InvokeAfterDelay(Action handler, TimeSpan delay)
+        {
+            if (_timer != null)
+            {
+                _timer.Stop();
+            }
+            else
+            {
+                _timer = new DispatcherTimer(DispatcherPriority.Normal);
+                _timer.Tick += (sender, args) =>
+                {
+                    var senderTimer = (DispatcherTimer)sender;
+
+                    if (senderTimer.Tag is Action action)
+                    {
+                        action();
+                    }
+
+                    senderTimer.Stop();
+                };
+            }
+
+            _timer.Tag = handler;
+            _timer.Interval = delay;
+
+            _timer.Start();
+        }
+
+        private void UpdateIsExpandedState()
+        {
+            if (!AllowAutoHide)
+            {
+                _timer?.Stop();
+
+                IsExpanded = true;
+            }
+            else
+            {
+                IsExpanded = IsPointerOver;
+            }
+        }
+
+        private void CollapseAfterDelay()
+        {
+            InvokeAfterDelay(Collapse, TimeSpan.FromSeconds(2));
+        }
+
+        private void ExpandAfterDelay()
+        {
+            InvokeAfterDelay(Expand, TimeSpan.FromMilliseconds(400));
+        }
+
+        private void Collapse()
+        {
+            IsExpanded = false;
+        }
+
+        private void Expand()
+        {
+            IsExpanded = true;
+        }
+
         private void LineUpClick(object sender, RoutedEventArgs e)
         {
             SmallDecrement();

src/Avalonia.Controls/Repeater/ItemsRepeater.cs

@@ -10,6 +10,7 @@ using Avalonia.Controls.Templates;
 using Avalonia.Data;
 using Avalonia.Input;
 using Avalonia.Layout;
+using Avalonia.Logging;
 using Avalonia.VisualTree;
 
 namespace Avalonia.Controls
@@ -80,6 +81,7 @@ namespace Avalonia.Controls
         static ItemsRepeater()
         {
             ClipToBoundsProperty.OverrideDefaultValue<ItemsRepeater>(true);
+            RequestBringIntoViewEvent.AddClassHandler<ItemsRepeater>((x, e) => x.OnRequestBringIntoView(e));
         }
 
         /// <summary>
@@ -305,6 +307,7 @@ namespace Avalonia.Controls
                             virtInfo.AutoRecycleCandidate &&
                             !virtInfo.KeepAlive)
                         {
+                            Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "AutoClear - {Index}", virtInfo.Index);
                             ClearElementImpl(element);
                         }
                     }
@@ -743,6 +746,11 @@ namespace Avalonia.Controls
             }
         }
 
+        private void OnRequestBringIntoView(RequestBringIntoViewEventArgs e)
+        {
+            _viewportManager.OnBringIntoViewRequested(e);
+        }
+
         private void InvalidateMeasureForLayout(object sender, EventArgs e) => InvalidateMeasure();
 
         private void InvalidateArrangeForLayout(object sender, EventArgs e) => InvalidateArrange();

src/Avalonia.Controls/Repeater/RepeaterLayoutContext.cs

@@ -7,6 +7,7 @@ using System;
 using System.Collections.Generic;
 using System.Text;
 using Avalonia.Layout;
+using Avalonia.Logging;
 
 namespace Avalonia.Controls
 {
@@ -58,7 +59,11 @@ namespace Avalonia.Controls
 
         protected override object GetItemAtCore(int index) => _owner.ItemsSourceView.GetAt(index);
 
-        protected override void RecycleElementCore(ILayoutable element) => _owner.ClearElementImpl((IControl)element);
+        protected override void RecycleElementCore(ILayoutable element)
+        {
+            Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "RepeaterLayout - RecycleElement: {Index}", _owner.GetElementIndex((IControl)element));
+            _owner.ClearElementImpl((IControl)element);
+        }
 
         protected override Rect RealizationRectCore() => _owner.RealizationWindow;
     }

src/Avalonia.Controls/Repeater/ViewManager.cs

@@ -11,6 +11,7 @@ using Avalonia.Controls.Templates;
 using Avalonia.Input;
 using Avalonia.Interactivity;
 using Avalonia.Layout;
+using Avalonia.Logging;
 using Avalonia.VisualTree;
 
 namespace Avalonia.Controls
@@ -60,11 +61,13 @@ namespace Avalonia.Controls
             if (suppressAutoRecycle)
             {
                 virtInfo.AutoRecycleCandidate = false;
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "GetElement: {Index} Not AutoRecycleCandidate:", virtInfo.Index);
             }
             else
             {
                 virtInfo.AutoRecycleCandidate = true;
                 virtInfo.KeepAlive = true;
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "GetElement: {Index} AutoRecycleCandidate:", virtInfo.Index);
             }
 
             return element;
@@ -107,10 +110,28 @@ namespace Avalonia.Controls
             }
         }
 
+        // We need to clear the datacontext to prevent crashes from happening,
+        //  however we only do that if we were the ones setting it.
+        // That is when one of the following is the case (numbering taken from line ~642):
+        // 1.2    No ItemTemplate, data is not a UIElement
+        // 2.1    ItemTemplate, data is not FrameworkElement
+        // 2.2.2  Itemtemplate, data is FrameworkElement, ElementFactory returned Element different to data
+        //
+        // In all of those three cases, we the ItemTemplateShim is NOT null.
+        // Luckily when we create the items, we store whether we were the once setting the DataContext.
         public void ClearElementToElementFactory(IControl element)
         {
             _owner.OnElementClearing(element);
 
+            var virtInfo = ItemsRepeater.GetVirtualizationInfo(element);
+            virtInfo.MoveOwnershipToElementFactory();
+
+            // During creation of this object, we were the one setting the DataContext, so clear it now.
+            if (virtInfo.MustClearDataContext)
+            {
+                element.DataContext = null;
+            }
+
             if (_owner.ItemTemplateShim != null)
             {
                 _owner.ItemTemplateShim.RecycleElement(_owner, element);
@@ -124,9 +145,6 @@ namespace Avalonia.Controls
                 }
             }
 
-            var virtInfo = ItemsRepeater.GetVirtualizationInfo(element);
-            virtInfo.MoveOwnershipToElementFactory();
-
             if (_lastFocusedElement == element)
             {
                 // Focused element is going away. Remove the tracked last focused element
@@ -594,11 +612,14 @@ namespace Avalonia.Controls
             {
                 virtInfo = ItemsRepeater.CreateAndInitializeVirtualizationInfo(element);
             }
+            // Clear flag
+            virtInfo.MustClearDataContext = false;
 
             if (data != element)
             {
                 // Prepare the element
                 element.DataContext = data;
+                virtInfo.MustClearDataContext = true;
             }
 
             virtInfo.MoveOwnershipToLayoutFromElementFactory(

src/Avalonia.Controls/Repeater/ViewportManager.cs

@@ -5,9 +5,15 @@
 
 using System;
 using System.Collections.Generic;
+using System.Reactive.Disposables;
 using System.Reactive.Linq;
 using System.Threading.Tasks;
+using Avalonia.Controls.Presenters;
+using Avalonia.Input;
 using Avalonia.Layout;
+using Avalonia.Logging;
+using Avalonia.Media;
+using Avalonia.Reactive;
 using Avalonia.Threading;
 using Avalonia.VisualTree;
 
@@ -35,8 +41,8 @@ namespace Avalonia.Controls
         // actually happened. This can happen in cases where no scrollviewer
         // in the parent chain can scroll in the shift direction.
         private Point _unshiftableShift;
-        private double _maximumHorizontalCacheLength = 0.0;
-        private double _maximumVerticalCacheLength = 0.0;
+        private double _maximumHorizontalCacheLength = 2.0;
+        private double _maximumVerticalCacheLength = 2.0;
         private double _horizontalCacheBufferPerSide;
         private double _verticalCacheBufferPerSide;
         private bool _isBringIntoViewInProgress;
@@ -184,6 +190,9 @@ namespace Avalonia.Controls
             // We tolerate viewport imprecisions up to 1 pixel to avoid invaliding layout too much.
             if (Math.Abs(_expectedViewportShift.X) > 1 || Math.Abs(_expectedViewportShift.Y) > 1)
             {
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Expecting viewport shift of ({Shift})",
+                    _owner.Layout.LayoutId, _expectedViewportShift);
+
                 // There are cases where we might be expecting a shift but not get it. We will
                 // be waiting for the effective viewport event but if the scroll viewer is not able
                 // to perform the shift (perhaps because it cannot scroll in negative offset),
@@ -229,14 +238,12 @@ namespace Avalonia.Controls
 
         public void OnElementPrepared(IControl element)
         {
-            // If we have an anchor element, we do not want the
-            // scroll anchor provider to start anchoring some other element.
-            ////element.CanBeScrollAnchor(true);
+            _scroller?.RegisterAnchorCandidate(element);
         }
 
-        public void OnElementCleared(ILayoutable element)
+        public void OnElementCleared(IControl element)
         {
-            ////element.CanBeScrollAnchor(false);
+            _scroller?.UnregisterAnchorCandidate(element);
         }
 
         public void OnOwnerMeasuring()
@@ -282,6 +289,7 @@ namespace Avalonia.Controls
         private void OnLayoutUpdated(object sender, EventArgs args)
         {
             _owner.LayoutUpdated -= OnLayoutUpdated;
+            _layoutUpdatedSubscribed = false;
             if (_managingViewportDisabled)
             {
                 return;
@@ -293,6 +301,10 @@ namespace Avalonia.Controls
             // that can scroll in the direction where the shift is expected.
             if (_pendingViewportShift.X != 0 || _pendingViewportShift.Y != 0)
             {
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Layout Updated with pending shift {Shift}- invalidating measure",
+                    _owner.Layout.LayoutId,
+                    _pendingViewportShift);
+
                 // Assume this is never going to come.
                 _unshiftableShift = new Point(
                     _unshiftableShift.X + _pendingViewportShift.X,
@@ -306,8 +318,11 @@ namespace Avalonia.Controls
 
         public void OnMakeAnchor(IControl anchor, bool isAnchorOutsideRealizedRange)
         {
-            _makeAnchorElement = anchor;
-            _isAnchorOutsideRealizedRange = isAnchorOutsideRealizedRange;
+            if (_makeAnchorElement != anchor)
+            {
+                _makeAnchorElement = anchor;
+                _isAnchorOutsideRealizedRange = isAnchorOutsideRealizedRange;
+            }
         }
 
         public void OnBringIntoViewRequested(RequestBringIntoViewEventArgs args)
@@ -328,26 +343,28 @@ namespace Avalonia.Controls
                 // Make sure that only the target child can be the anchor during the bring into view operation.
                 foreach (var child in _owner.Children)
                 {
-                    ////if (child.CanBeScrollAnchor && child != targetChild)
-                    ////{
-                    ////    child.CanBeScrollAnchor = false;
-                    ////}
+                    if (child != targetChild)
+                    {
+                        _scroller.UnregisterAnchorCandidate(child);
+                    }
                 }
 
-                // Register to rendering event to go back to how things were before where any child can be the anchor.
-                _isBringIntoViewInProgress = true;
-                ////if (!m_renderingToken)
-                ////{
-                ////    winrt::Windows::UI::Xaml::Media::CompositionTarget compositionTarget{ nullptr };
-                ////    m_renderingToken = compositionTarget.Rendering(winrt::auto_revoke, { this, &ViewportManagerWithPlatformFeatures::OnCompositionTargetRendering });
-                ////}
+                // Register action to go back to how things were before where any child can be the anchor. Here,
+                // WinUI uses CompositionTarget.Rendering but we don't currently have that, so post an action to
+                // run *after* rendering has completed (priority needs to be lower than Render as Transformed
+                // bounds must have been set in order for OnEffectiveViewportChanged to trigger).
+                if (!_isBringIntoViewInProgress)
+                {
+                    _isBringIntoViewInProgress = true;
+                    Dispatcher.UIThread.Post(OnCompositionTargetRendering, DispatcherPriority.Loaded);
+                }
             }
         }
 
         private IControl GetImmediateChildOfRepeater(IControl descendant)
         {
             var targetChild = descendant;
-            var parent = descendant.Parent;
+            var parent = (IControl)descendant.VisualParent;
             while (parent != null && parent != _owner)
             {
                 targetChild = parent;
@@ -362,26 +379,50 @@ namespace Avalonia.Controls
             return targetChild;
         }
 
-        public void ResetScrollers()
+        private void OnCompositionTargetRendering()
         {
-            _scroller = null;
-            _effectiveViewportChangedRevoker?.Dispose();
-            _effectiveViewportChangedRevoker = null;
-            _ensuredScroller = false;
+            _isBringIntoViewInProgress = false;
+            _makeAnchorElement = null;
+
+            if (_scroller is object)
+            {
+                foreach (var child in _owner.Children)
+                {
+                    var info = ItemsRepeater.GetVirtualizationInfo(child);
+
+                    if (info.IsRealized && info.IsHeldByLayout)
+                    {
+                        _scroller.RegisterAnchorCandidate(child);
+                    }
+                }
+            }
+
+            // HACK: Invalidate measure now that the anchor has been removed so that a layout can be
+            // done with a proper realization rect. This is a hack not present upstream to try to fix
+            // https://github.com/microsoft/microsoft-ui-xaml/issues/1422
+            TryInvalidateMeasure();
         }
 
-        private void OnEffectiveViewportChanged(TransformedBounds? bounds)
+        public void ResetScrollers()
         {
-            if (!bounds.HasValue)
+            if (_scroller is object)
             {
-                return;
+                foreach (var child in _owner.Children)
+                {
+                    _scroller.UnregisterAnchorCandidate(child);
+                }
+
+                _scroller = null;
             }
 
-            var globalClip = bounds.Value.Clip;
-            var transform = _owner.GetVisualRoot().TransformToVisual(_owner).Value;
-            var clip = globalClip.TransformToAABB(transform);
-            var effectiveViewport = clip.Intersect(bounds.Value.Bounds);
+            _effectiveViewportChangedRevoker?.Dispose();
+            _effectiveViewportChangedRevoker = null;
+            _ensuredScroller = false;
+        }
 
+        private void OnEffectiveViewportChanged(Rect effectiveViewport)
+        {
+            Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: EffectiveViewportChanged event callback", _owner.Layout.LayoutId);
             UpdateViewport(effectiveViewport);
 
             _pendingViewportShift = default;
@@ -397,6 +438,7 @@ namespace Avalonia.Controls
             if (_layoutUpdatedSubscribed)
             {
                 _owner.LayoutUpdated -= OnLayoutUpdated;
+                _layoutUpdatedSubscribed = false;
             }
         }
 
@@ -437,10 +479,17 @@ namespace Avalonia.Controls
         private void UpdateViewport(Rect viewport)
         {
             var currentVisibleWindow = viewport;
+            var previousVisibleWindow = _visibleWindow;
+
+            Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Effective Viewport: ({Before})->({After})",
+                _owner.Layout.LayoutId,
+                previousVisibleWindow,
+                viewport);
 
             if (-currentVisibleWindow.X <= ItemsRepeater.ClearedElementsArrangePosition.X &&
                 -currentVisibleWindow.Y <= ItemsRepeater.ClearedElementsArrangePosition.Y)
             {
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Viewport is invalid. visible window cleared", _owner.Layout.LayoutId);
                 // We got cleared.
                 _visibleWindow = default;
             }
@@ -449,7 +498,14 @@ namespace Avalonia.Controls
                 _visibleWindow = currentVisibleWindow;
             }
 
-            TryInvalidateMeasure();
+            if (_visibleWindow != previousVisibleWindow)
+            {
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Used Viewport: ({Before})->({After})",
+                    _owner.Layout.LayoutId,
+                    previousVisibleWindow,
+                    currentVisibleWindow);
+                TryInvalidateMeasure();
+            }
         }
 
         private static void ValidateCacheLength(double cacheLength)
@@ -468,6 +524,7 @@ namespace Avalonia.Controls
                 // We invalidate measure instead of just invalidating arrange because
                 // we don't invalidate measure in UpdateViewport if the view is changing to
                 // avoid layout cycles.
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Invalidating measure due to viewport change", _owner.Layout.LayoutId);
                 _owner.InvalidateMeasure();
             }
         }
@@ -476,16 +533,32 @@ namespace Avalonia.Controls
         {
             // HACK: This is a bit of a hack. We need the effective viewport of the ItemsRepeater -
             // we can get this from TransformedBounds, but this property is updated after layout has
-            // run, resulting in the UI being updated too late when scrolling quickly. We can
-            // partially remedey this by triggering also on Bounds changes, but this won't work so 
-            // well for nested ItemsRepeaters.
+            // run, which is too late. Instead, for now lets just hook into an internal event on
+            // ScrollContentPresenter to find out what the offset and viewport will be after arrange
+            // and use those values. Note that this doesn't handle nested ScrollViewers at all, but
+            // it's enough to get scrolling to non-uniformly sized items working for now.
             //
-            // UWP uses the EffectiveBoundsChanged event (which I think was implemented specially
-            // for this case): we need to implement that in Avalonia.
-            return control.GetObservable(Visual.TransformedBoundsProperty)
-                .Merge(control.GetObservable(Visual.BoundsProperty).Select(_ => control.TransformedBounds))
-                .Skip(1)
-                .Subscribe(OnEffectiveViewportChanged);
+            // UWP uses the EffectiveViewportChanged event (which I think was implemented specially
+            // for this case): we need to implement that in Avalonia, but the semantics of it aren't
+            // clear to me. Hopefully the source for this event will be released with WinUI 3.
+            if (control.VisualParent is ScrollContentPresenter scp)
+            {
+                scp.PreArrange += ScrollContentPresenterPreArrange;
+                return Disposable.Create(() => scp.PreArrange -= ScrollContentPresenterPreArrange);
+            }
+
+            return Disposable.Empty;
+        }
+
+        private void ScrollContentPresenterPreArrange(object sender, VectorEventArgs e)
+        {
+            var scp = (ScrollContentPresenter)sender;
+            var effectiveViewport = new Rect((Point)scp.Offset, new Size(e.Vector.X, e.Vector.Y));
+
+            if (effectiveViewport != _visibleWindow)
+            {
+                OnEffectiveViewportChanged(effectiveViewport);
+            }
         }
 
         private class ScrollerInfo

src/Avalonia.Controls/Repeater/VirtualizationInfo.cs

@@ -36,6 +36,7 @@ namespace Avalonia.Controls
         public bool IsHeldByLayout => Owner == ElementOwner.Layout;
         public bool IsRealized => IsHeldByLayout || Owner == ElementOwner.PinnedPool;
         public bool IsInUniqueIdResetPool => Owner == ElementOwner.UniqueIdResetPool;
+        public bool MustClearDataContext { get; set; }
         public bool KeepAlive { get; set; }
         public ElementOwner Owner { get; private set; } = ElementOwner.ElementFactory;
         public string UniqueId { get; private set; }

src/Avalonia.Controls/ScrollViewer.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Reactive.Linq;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Input;
@@ -166,6 +167,18 @@ namespace Avalonia.Controls
                 nameof(VerticalScrollBarVisibility),
                 ScrollBarVisibility.Auto);
 
+        /// <summary>
+        /// Defines the <see cref="IsExpandedProperty"/> property.
+        /// </summary>
+        public static readonly DirectProperty<ScrollViewer, bool> IsExpandedProperty =
+            ScrollBar.IsExpandedProperty.AddOwner<ScrollViewer>(o => o.IsExpanded);
+
+        /// <summary>
+        /// Defines the <see cref="AllowAutoHide"/> property.
+        /// </summary>
+        public static readonly StyledProperty<bool> AllowAutoHideProperty =
+            ScrollBar.AllowAutoHideProperty.AddOwner<ScrollViewer>();
+
         /// <summary>
         /// Defines the <see cref="ScrollChanged"/> event.
         /// </summary>
@@ -186,6 +199,8 @@ namespace Avalonia.Controls
         private Size _oldViewport;
         private Size _largeChange;
         private Size _smallChange = new Size(DefaultSmallChange, DefaultSmallChange);
+        private bool _isExpanded;
+        private IDisposable _scrollBarExpandSubscription;
 
         /// <summary>
         /// Initializes static members of the <see cref="ScrollViewer"/> class.
@@ -244,9 +259,7 @@ namespace Avalonia.Controls
 
             set
             {
-                value = ValidateOffset(this, value);
-
-                if (SetAndRaise(OffsetProperty, ref _offset, value))
+                if (SetAndRaise(OffsetProperty, ref _offset, CoerceOffset(Extent, Viewport, value)))
                 {
                     CalculatedPropertiesChanged();
                 }
@@ -316,6 +329,9 @@ namespace Avalonia.Controls
             get { return VerticalScrollBarVisibility != ScrollBarVisibility.Disabled; }
         }
 
+        /// <inheritdoc/>
+        public IControl CurrentAnchor => (Presenter as IScrollAnchorProvider)?.CurrentAnchor;
+
         /// <summary>
         /// Gets the maximum horizontal scrollbar value.
         /// </summary>
@@ -382,8 +398,23 @@ namespace Avalonia.Controls
             get { return _viewport.Height; }
         }
 
-        /// <inheritdoc/>
-        IControl IScrollAnchorProvider.CurrentAnchor => null; // TODO: Implement
+        /// <summary>
+        /// Gets a value that indicates whether any scrollbar is expanded.
+        /// </summary>
+        public bool IsExpanded
+        {
+            get => _isExpanded;
+            private set => SetAndRaise(ScrollBar.IsExpandedProperty, ref _isExpanded, value);
+        }
+
+        /// <summary>
+        /// Gets a value that indicates whether scrollbars can hide itself when user is not interacting with it.
+        /// </summary>
+        public bool AllowAutoHide
+        {
+            get => GetValue(AllowAutoHideProperty);
+            set => SetValue(AllowAutoHideProperty, value);
+        }
 
         /// <summary>
         /// Scrolls the content up one line.
@@ -473,14 +504,16 @@ namespace Avalonia.Controls
             control.SetValue(VerticalScrollBarVisibilityProperty, value);
         }
 
-        void IScrollAnchorProvider.RegisterAnchorCandidate(IControl element)
+        /// <inheritdoc/>
+        public void RegisterAnchorCandidate(IControl element)
         {
-            // TODO: Implement
+            (Presenter as IScrollAnchorProvider)?.RegisterAnchorCandidate(element);
         }
 
-        void IScrollAnchorProvider.UnregisterAnchorCandidate(IControl element)
+        /// <inheritdoc/>
+        public void UnregisterAnchorCandidate(IControl element)
         {
-            // TODO: Implement
+            (Presenter as IScrollAnchorProvider)?.UnregisterAnchorCandidate(element);
         }
 
         protected override bool RegisterContentPresenter(IContentPresenter presenter)
@@ -517,22 +550,6 @@ namespace Avalonia.Controls
             return double.IsNaN(result) ? 0 : result;
         }
 
-        private static Vector ValidateOffset(AvaloniaObject o, Vector value)
-        {
-            ScrollViewer scrollViewer = o as ScrollViewer;
-
-            if (scrollViewer != null)
-            {
-                var extent = scrollViewer.Extent;
-                var viewport = scrollViewer.Viewport;
-                return CoerceOffset(extent, viewport, value);
-            }
-            else
-            {
-                return value;
-            }
-        }
-
         private void ChildChanged(IControl child)
         {
             if (_logicalScrollable is object)
@@ -630,6 +647,54 @@ namespace Avalonia.Controls
             RaiseEvent(e);
         }
 
+        protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
+        {
+            base.OnApplyTemplate(e);
+
+            _scrollBarExpandSubscription?.Dispose();
+
+            _scrollBarExpandSubscription = SubscribeToScrollBars(e);
+        }
+
+        private IDisposable SubscribeToScrollBars(TemplateAppliedEventArgs e)
+        {
+            static IObservable<bool> GetExpandedObservable(ScrollBar scrollBar)
+            {
+                return scrollBar?.GetObservable(ScrollBar.IsExpandedProperty);
+            }
+
+            var horizontalScrollBar = e.NameScope.Find<ScrollBar>("PART_HorizontalScrollBar");
+            var verticalScrollBar = e.NameScope.Find<ScrollBar>("PART_VerticalScrollBar");
+
+            var horizontalExpanded = GetExpandedObservable(horizontalScrollBar);
+            var verticalExpanded = GetExpandedObservable(verticalScrollBar);
+
+            IObservable<bool> actualExpanded = null;
+
+            if (horizontalExpanded != null && verticalExpanded != null)
+            {
+                actualExpanded = horizontalExpanded.CombineLatest(verticalExpanded, (h, v) => h || v);
+            }
+            else
+            {
+                if (horizontalExpanded != null)
+                {
+                    actualExpanded = horizontalExpanded;
+                }
+                else if (verticalExpanded != null)
+                {
+                    actualExpanded = verticalExpanded;
+                }
+            }
+
+            return actualExpanded?.Subscribe(OnScrollBarExpandedChanged);
+        }
+
+        private void OnScrollBarExpandedChanged(bool isExpanded)
+        {
+            IsExpanded = isExpanded;
+        }
+
         private void OnLayoutUpdated(object sender, EventArgs e) => RaiseScrollChanged();
 
         private void RaiseScrollChanged()

src/Avalonia.Controls/TreeViewItem.cs

@@ -49,6 +49,7 @@ namespace Avalonia.Controls
         static TreeViewItem()
         {
             SelectableMixin.Attach<TreeViewItem>(IsSelectedProperty);
+            PressedMixin.Attach<TreeViewItem>();
             FocusableProperty.OverrideDefaultValue<TreeViewItem>(true);
             ItemsPanelProperty.OverrideDefaultValue<TreeViewItem>(DefaultPanel);
             ParentProperty.Changed.AddClassHandler<TreeViewItem>((o, e) => o.OnParentChanged(e));

src/Avalonia.Layout/AttachedLayout.cs

@@ -12,7 +12,7 @@ namespace Avalonia.Layout
     /// </summary>
     public abstract class AttachedLayout : AvaloniaObject
     {
-        internal string LayoutId { get; set; }
+        public string LayoutId { get; set; }
 
         /// <summary>
         /// Occurs when the measurement state (layout) has been invalidated.

src/Avalonia.Layout/ElementManager.cs

@@ -7,6 +7,7 @@ using System;
 using System.Collections.Generic;
 using System.Collections.Specialized;
 using Avalonia.Layout.Utils;
+using Avalonia.Logging;
 
 namespace Avalonia.Layout
 {
@@ -78,6 +79,7 @@ namespace Avalonia.Layout
                 {
                     // Sentinel. Create the element now since we need it.
                     int dataIndex = GetDataIndexFromRealizedRangeIndex(realizedIndex);
+                    Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "Creating element for sentinal with data index {Index}", dataIndex);
                     element = _context.GetOrCreateElementAt(
                         dataIndex,
                         ElementRealizationOptions.ForceCreate | ElementRealizationOptions.SuppressAutoRecycle);
@@ -232,6 +234,8 @@ namespace Avalonia.Layout
                 {
                     Insert(0, dataIndex, element);
                 }
+
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Created element for index {index}", layoutId, dataIndex);
             }
         }
 

src/Avalonia.Layout/FlowLayoutAlgorithm.cs

@@ -5,6 +5,7 @@
 
 using System;
 using System.Collections.Specialized;
+using Avalonia.Logging;
 
 namespace Avalonia.Layout
 {
@@ -82,6 +83,9 @@ namespace Avalonia.Layout
             // If minor size is infinity, there is only one line and no need to align that line.
             _scrollOrientationSameAsFlow = double.IsInfinity(_orientation.Minor(availableSize));
             var realizationRect = RealizationRect;
+            Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: MeasureLayout Realization({Rect})",
+                layoutId,
+                realizationRect);
 
             var suggestedAnchorIndex = _context.RecommendedAnchorIndex;
             if (_elementManager.IsIndexValidInData(suggestedAnchorIndex))
@@ -100,6 +104,7 @@ namespace Avalonia.Layout
             Generate(GenerateDirection.Backward, anchorIndex, availableSize, minItemSpacing, lineSpacing, maxItemsPerLine, disableVirtualization, layoutId);
             if (isWrapping && IsReflowRequired())
             {
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Reflow Pass", layoutId);
                 var firstElementBounds = _elementManager.GetLayoutBoundsForRealizedIndex(0);
                 _orientation.SetMinorStart(ref firstElementBounds, 0);
                 _elementManager.SetLayoutBoundsForRealizedIndex(0, firstElementBounds);
@@ -121,6 +126,7 @@ namespace Avalonia.Layout
             LineAlignment lineAlignment,
             string layoutId)
         {
+            Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: ArrangeLayout", layoutId);
             ArrangeVirtualizingLayout(finalSize, lineAlignment, isWrapping, layoutId);
 
             return new Size(
@@ -184,6 +190,7 @@ namespace Avalonia.Layout
 
                 if (isAnchorSuggestionValid)
                 {
+                    Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Using suggested anchor {Anchor}", layoutId, suggestedAnchorIndex);
                     anchorIndex = _algorithmCallbacks.Algorithm_GetAnchorForTargetElement(
                         suggestedAnchorIndex,
                         availableSize,
@@ -223,6 +230,9 @@ namespace Avalonia.Layout
                 }
                 else if (needAnchorColumnRevaluation || !isRealizationWindowConnected)
                 {
+                    if (needAnchorColumnRevaluation) { Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: NeedAnchorColumnReevaluation", layoutId); }
+                    if (!isRealizationWindowConnected) { Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Disconnected Window", layoutId); }
+
                     // The anchor is based on the realization window because a connected ItemsRepeater might intersect the realization window
                     // but not the visible window. In that situation, we still need to produce a valid anchor.
                     var anchorInfo = _algorithmCallbacks.Algorithm_GetAnchorForRealizationRect(availableSize, context);
@@ -231,6 +241,7 @@ namespace Avalonia.Layout
                 }
                 else
                 {
+                    Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Connected Window - picking first realized element as anchor", layoutId);
                     // No suggestion - just pick first in realized range
                     anchorIndex = _elementManager.GetDataIndexFromRealizedRangeIndex(0);
                     var firstElementBounds = _elementManager.GetLayoutBoundsForRealizedIndex(0);
@@ -238,12 +249,14 @@ namespace Avalonia.Layout
                 }
             }
 
+            Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Picked anchor: {Anchor}", layoutId, anchorIndex);
             _firstRealizedDataIndexInsideRealizationWindow = _lastRealizedDataIndexInsideRealizationWindow = anchorIndex;
             if (_elementManager.IsIndexValidInData(anchorIndex))
             {
                 if (!_elementManager.IsDataIndexRealized(anchorIndex))
                 {
                     // Disconnected, throw everything and create new anchor
+                    Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId} Disconnected Window - throwing away all realized elements", layoutId);
                     _elementManager.ClearRealizedRange();
 
                     var anchor = _context.GetOrCreateElementAt(anchorIndex, ElementRealizationOptions.ForceCreate | ElementRealizationOptions.SuppressAutoRecycle);
@@ -254,9 +267,17 @@ namespace Avalonia.Layout
                 var desiredSize = MeasureElement(anchorElement, anchorIndex, availableSize, _context);
                 var layoutBounds = new Rect(anchorPosition.X, anchorPosition.Y, desiredSize.Width, desiredSize.Height);
                 _elementManager.SetLayoutBoundsForDataIndex(anchorIndex, layoutBounds);
+
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Layout bounds of anchor {anchor} are ({Bounds})",
+                    layoutId,
+                    anchorIndex,
+                    layoutBounds);
             }
             else
             {
+                // Throw everything away
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId} Anchor index is not valid - throwing away all realized elements",
+                    layoutId);
                 _elementManager.ClearRealizedRange();
             }
 
@@ -280,6 +301,12 @@ namespace Avalonia.Layout
             if (anchorIndex != -1)
             {
                 int step = (direction == GenerateDirection.Forward) ? 1 : -1;
+
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Generating {Direction} from anchor {Anchor}",
+                    layoutId,
+                    direction,
+                    anchorIndex);
+
                 int previousIndex = anchorIndex;
                 int currentIndex = anchorIndex + step;
                 var anchorBounds = _elementManager.GetLayoutBoundsForDataIndex(anchorIndex);
@@ -365,6 +392,10 @@ namespace Avalonia.Layout
                                         _orientation.SetMajorStart(ref bounds, previousLineOffset - lineMajorSize - lineSpacing);
                                         _orientation.SetMajorSize(ref bounds, lineMajorSize);
                                         _elementManager.SetLayoutBoundsForDataIndex(dataIndex, bounds);
+                                        Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Corrected Layout bounds of element {Index} are ({Bounds})",
+                                            layoutId,
+                                            dataIndex,
+                                            bounds);
                                     }
                                 }
                             }
@@ -387,6 +418,11 @@ namespace Avalonia.Layout
                     }
 
                     _elementManager.SetLayoutBoundsForDataIndex(currentIndex, currentBounds);
+
+                    Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Layout bounds of element {Index} are ({Bounds}).",
+                        layoutId,
+                        currentIndex,
+                        currentBounds);
                     previousIndex = currentIndex;
                     currentIndex += step;
                 }
@@ -394,20 +430,17 @@ namespace Avalonia.Layout
                 // If we did not reach the top or bottom of the extent, we realized one 
                 // extra item before we knew we were outside the realization window. Do not
                 // account for that element in the indicies inside the realization window.
-                if (count > 0)
+                if (direction == GenerateDirection.Forward)
                 {
-                    if (direction == GenerateDirection.Forward)
-                    {
-                        int dataCount = _context.ItemCount;
-                        _lastRealizedDataIndexInsideRealizationWindow = previousIndex == dataCount - 1 ? dataCount - 1 : previousIndex - 1;
-                        _lastRealizedDataIndexInsideRealizationWindow = Math.Max(0, _lastRealizedDataIndexInsideRealizationWindow);
-                    }
-                    else
-                    {
-                        int dataCount = _context.ItemCount;
-                        _firstRealizedDataIndexInsideRealizationWindow = previousIndex == 0 ? 0 : previousIndex + 1;
-                        _firstRealizedDataIndexInsideRealizationWindow = Math.Min(dataCount - 1, _firstRealizedDataIndexInsideRealizationWindow);
-                    }
+                    int dataCount = _context.ItemCount;
+                    _lastRealizedDataIndexInsideRealizationWindow = previousIndex == dataCount - 1 ? dataCount - 1 : previousIndex - 1;
+                    _lastRealizedDataIndexInsideRealizationWindow = Math.Max(0, _lastRealizedDataIndexInsideRealizationWindow);
+                }
+                else
+                {
+                    int dataCount = _context.ItemCount;
+                    _firstRealizedDataIndexInsideRealizationWindow = previousIndex == 0 ? 0 : previousIndex + 1;
+                    _firstRealizedDataIndexInsideRealizationWindow = Math.Min(dataCount - 1, _firstRealizedDataIndexInsideRealizationWindow);
                 }
 
                 _elementManager.DiscardElementsOutsideWindow(direction == GenerateDirection.Forward, currentIndex);
@@ -508,6 +541,7 @@ namespace Avalonia.Layout
                 lastDataIndex,
                 lastBounds);
 
+            Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId} Extent: ({Bounds})", layoutId, extent);
             return extent;
         }
 
@@ -676,6 +710,11 @@ namespace Avalonia.Layout
                 }
 
                 var element = _elementManager.GetAt(rangeIndex);
+
+                Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Arranging element {Index} at ({Bounds})",
+                    layoutId,
+                    _elementManager.GetDataIndexFromRealizedRangeIndex(rangeIndex),
+                    bounds);
                 element.Arrange(bounds);
             }
         }

src/Avalonia.Layout/LayoutHelper.cs

@@ -118,7 +118,7 @@ namespace Avalonia.Layout
             double newValue;
 
             // If DPI == 1, don't use DPI-aware rounding.
-            if (!MathUtilities.AreClose(dpiScale, 1.0))
+            if (!MathUtilities.IsOne(dpiScale))
             {
                 newValue = Math.Round(value * dpiScale) / dpiScale;
 

src/Avalonia.Layout/LayoutManager.cs

@@ -23,10 +23,10 @@ namespace Avalonia.Layout
             _executeLayoutPass = ExecuteLayoutPass;
         }
 
-        public event EventHandler? LayoutUpdated;
+        public virtual event EventHandler? LayoutUpdated;
 
         /// <inheritdoc/>
-        public void InvalidateMeasure(ILayoutable control)
+        public virtual void InvalidateMeasure(ILayoutable control)
         {
             control = control ?? throw new ArgumentNullException(nameof(control));
             Dispatcher.UIThread.VerifyAccess();
@@ -47,7 +47,7 @@ namespace Avalonia.Layout
         }
 
         /// <inheritdoc/>
-        public void InvalidateArrange(ILayoutable control)
+        public virtual void InvalidateArrange(ILayoutable control)
         {
             control = control ?? throw new ArgumentNullException(nameof(control));
             Dispatcher.UIThread.VerifyAccess();
@@ -67,7 +67,7 @@ namespace Avalonia.Layout
         }
 
         /// <inheritdoc/>
-        public void ExecuteLayoutPass()
+        public virtual void ExecuteLayoutPass()
         {
             const int MaxPasses = 3;
 
@@ -131,7 +131,7 @@ namespace Avalonia.Layout
         }
 
         /// <inheritdoc/>
-        public void ExecuteInitialLayoutPass(ILayoutRoot root)
+        public virtual void ExecuteInitialLayoutPass(ILayoutRoot root)
         {
             try
             {

src/Avalonia.Layout/LayoutQueue.cs

@@ -77,7 +77,7 @@ namespace Avalonia.Layout
             {
                 if (_shouldEnqueue(item.Key))
                 {
-                    _loopQueueInfo[item.Key] = new Info() { Active = true, Count = item.Value.Count + 1 };
+                    _loopQueueInfo[item.Key] = new Info() { Active = true, Count = 0 };
                     _inner.Enqueue(item.Key);
                 }
             }

src/Avalonia.Layout/NonVirtualizingStackLayout.cs

@@ -112,7 +112,9 @@ namespace Avalonia.Layout
                 u = (isVertical ? bounds.Bottom : bounds.Right) + spacing;
             }
 
-            return new Size(bounds.Right, bounds.Bottom);
+            return new Size(
+                Math.Max(finalSize.Width, bounds.Width),
+                Math.Max(finalSize.Height, bounds.Height));
         }
 
         private static Rect LayoutVertical(ILayoutable element, double y, Size constraint)

src/Avalonia.Layout/StackLayout.cs

@@ -6,6 +6,7 @@
 using System;
 using System.Collections.Specialized;
 using Avalonia.Data;
+using Avalonia.Logging;
 
 namespace Avalonia.Layout
 {
@@ -107,8 +108,15 @@ namespace Avalonia.Layout
                             _orientation.MajorStart(extent) + 
                             (remainingItems * averageElementSize));
                 }
+                else
+                {
+                    Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Estimating extent with no realized elements",
+                        LayoutId);
+                }
             }
 
+            Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Extent is ({Size}). Based on average {Average}",
+                LayoutId, extent.Size, averageElementSize);
             return extent;
         }
 

src/Avalonia.Layout/UniformGridLayout.cs

@@ -6,6 +6,7 @@
 using System;
 using System.Collections.Specialized;
 using Avalonia.Data;
+using Avalonia.Logging;
 
 namespace Avalonia.Layout
 {
@@ -379,8 +380,14 @@ namespace Avalonia.Layout
                         ref extent,
                         _orientation.MajorEnd(lastRealizedLayoutBounds) - _orientation.MajorStart(extent) + (remainingItems / itemsPerLine) * lineSize);
                 }
+                else
+                {
+                    Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Estimating extent with no realized elements", LayoutId);
+                }
             }
 
+            Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Extent is ({Size}). Based on lineSize {LineSize} and items per line {ItemsPerLine}",
+                LayoutId, extent.Size, lineSize, itemsPerLine);
             return extent;
         }
 

src/Avalonia.Themes.Default/ToggleSwitch.xaml

@@ -3,8 +3,8 @@
         xmlns:sys="clr-namespace:System;assembly=netstandard">
   <Styles.Resources>
     <Thickness x:Key="ToggleSwitchTopHeaderMargin">0,0,0,6</Thickness>
-    <x:Double x:Key="ToggleSwitchPreContentMargin">6</x:Double>
-    <x:Double x:Key="ToggleSwitchPostContentMargin">6</x:Double>
+    <GridLength x:Key="ToggleSwitchPreContentMargin">6</GridLength>
+    <GridLength x:Key="ToggleSwitchPostContentMargin">6</GridLength>
     <x:Double x:Key="ToggleSwitchThemeMinWidth">154</x:Double>
     <x:Double x:Key="KnobOnPosition">20</x:Double>
     <x:Double x:Key="KnobOffPosition">0</x:Double>

src/Avalonia.Themes.Fluent/Accents/BaseDark.xaml

@@ -140,7 +140,12 @@
     <SolidColorBrush x:Key="SystemControlTransientBorderBrush" Color="#000000" Opacity="0.36" />
     <SolidColorBrush x:Key="SystemControlHighlightListLowRevealBackgroundBrush" Color="{StaticResource SystemListMediumColor}" />
     <SolidColorBrush x:Key="SystemControlHighlightListMediumRevealBackgroundBrush" Color="{StaticResource SystemListMediumColor}" />
-    <SolidColorBrush x:Key="SystemControlHighlightAccentRevealBackgroundBrush" Color="{StaticResource SystemAccentColor}" />
+    <SolidColorBrush x:Key="SystemControlHighlightAccentRevealBackgroundBrush" Color="{DynamicResource SystemAccentColor}" />
+    <SolidColorBrush x:Key="SystemControlHighlightAccent3RevealBackgroundBrush" Color="{DynamicResource SystemAccentColor}" Opacity="0.6" />
+    <SolidColorBrush x:Key="SystemControlHighlightAccent2RevealBackgroundBrush" Color="{DynamicResource SystemAccentColor}" Opacity="0.8" />
+    <SolidColorBrush x:Key="SystemControlBackgroundChromeWhiteRevealBorderBrush" Color="{StaticResource SystemChromeWhiteColor}" />
+    <SolidColorBrush x:Key="SystemControlHighlightAltTransparentRevealBorderBrush" Color="Transparent" />
+    <SolidColorBrush x:Key="SystemControlBackgroundTransparentRevealBorderBrush" Color="Transparent" />
     <!-- TODO implement AcrylicBrush -->
     <!--<AcrylicBrush x:Key="SystemControlTransientBackgroundBrush" BackgroundSource="HostBackdrop" TintColor="{StaticResource SystemChromeAltHighColor}" TintOpacity="0.8" FallbackColor="{StaticResource SystemChromeMediumLowColor}" />-->
     <SolidColorBrush x:Key="SystemControlTransientBackgroundBrush" Color="{StaticResource SystemChromeMediumLowColor}" />

src/Avalonia.Themes.Fluent/Accents/BaseLight.xaml

@@ -140,7 +140,12 @@
     <SolidColorBrush x:Key="SystemControlTransientBorderBrush" Color="#000000" Opacity="0.14" />
     <SolidColorBrush x:Key="SystemControlHighlightListLowRevealBackgroundBrush" Color="{StaticResource SystemListMediumColor}" />
     <SolidColorBrush x:Key="SystemControlHighlightListMediumRevealBackgroundBrush" Color="{StaticResource SystemListMediumColor}" />
-    <SolidColorBrush x:Key="SystemControlHighlightAccentRevealBackgroundBrush" Color="{StaticResource SystemAccentColor}" />
+    <SolidColorBrush x:Key="SystemControlHighlightAccentRevealBackgroundBrush" Color="{DynamicResource SystemAccentColor}" />
+    <SolidColorBrush x:Key="SystemControlHighlightAccent3RevealBackgroundBrush" Color="{DynamicResource SystemAccentColor}" Opacity="0.6" />
+    <SolidColorBrush x:Key="SystemControlHighlightAccent2RevealBackgroundBrush" Color="{DynamicResource SystemAccentColor}" Opacity="0.8" />
+    <SolidColorBrush x:Key="SystemControlBackgroundChromeWhiteRevealBorderBrush" Color="{StaticResource SystemChromeWhiteColor}" />
+    <SolidColorBrush x:Key="SystemControlHighlightAltTransparentRevealBorderBrush" Color="Transparent" />
+    <SolidColorBrush x:Key="SystemControlBackgroundTransparentRevealBorderBrush" Color="Transparent" />
     <!-- TODO implement AcrylicBrush -->
     <!--<AcrylicBrush x:Key="SystemControlTransientBackgroundBrush" BackgroundSource="HostBackdrop" TintColor="{StaticResource SystemChromeAltHighColor}" TintOpacity="0.8" FallbackColor="{StaticResource SystemChromeMediumLowColor}" />-->
     <SolidColorBrush x:Key="SystemControlTransientBackgroundBrush" Color="{StaticResource SystemChromeMediumLowColor}" />

src/Avalonia.Themes.Fluent/Accents/FluentBaseDark.xaml

@@ -19,7 +19,6 @@
     <Color x:Key="SystemChromeBlackMediumColor">#FF000000</Color>
     <Color x:Key="SystemChromeBlackMediumLowColor">#FF000000</Color>
     <Color x:Key="SystemChromeDisabledHighColor">#FF333333</Color>
-    <Color x:Key="SystemChromeDisabledLowColor">#FF9A9A9A</Color>
     <Color x:Key="SystemChromeGrayColor">#FF808080</Color>
     <Color x:Key="SystemChromeHighColor">#FF808080</Color>
     <Color x:Key="SystemChromeLowColor">#FF151515</Color>
@@ -471,5 +470,56 @@
     <SolidColorBrush x:Key="PivotNavButtonPressedBackgroundThemeBrush" Color="#BD292929" />
     <SolidColorBrush x:Key="PivotNavButtonPressedBorderThemeBrush" Color="#BD292929" />
     <SolidColorBrush x:Key="PivotNavButtonPressedForegroundThemeBrush" Color="#FFFFFFFF" />
+
+    <!-- BaseResources for ScrollBar.xaml -->
+    <StaticResource x:Key="ScrollBarBackground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBackgroundPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBackgroundDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarForeground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrush" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrushPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrushDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundPointerOver" ResourceKey="SystemControlBackgroundListLowBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundPressed" ResourceKey="SystemControlBackgroundBaseMediumBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrush" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushPressed" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForeground" ResourceKey="SystemControlForegroundBaseHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundPointerOver" ResourceKey="SystemControlForegroundBaseHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundPressed" ResourceKey="SystemControlForegroundAltHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundDisabled" ResourceKey="SystemControlForegroundBaseLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFill" ResourceKey="SystemControlForegroundChromeDisabledLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillPointerOver" ResourceKey="SystemControlBackgroundBaseMediumLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillPressed" ResourceKey="SystemControlBackgroundBaseMediumBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <SolidColorBrush x:Key="ScrollBarTrackFill" Color="{StaticResource SystemChromeMediumColor}" Opacity="0.9" />
+    <SolidColorBrush x:Key="ScrollBarTrackFillPointerOver" Color="{StaticResource SystemChromeMediumColor}" Opacity="0.9" />
+    <StaticResource x:Key="ScrollBarTrackFillDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStroke" ResourceKey="SystemControlForegroundTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStrokePointerOver" ResourceKey="SystemControlForegroundTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStrokeDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <StaticResource x:Key="ScrollBarPanningThumbBackgroundDisabled" ResourceKey="SystemControlDisabledChromeHighBrush" />
+    <StaticResource x:Key="ScrollBarThumbBackgroundColor" ResourceKey="SystemBaseLowColor" />
+    <StaticResource x:Key="ScrollBarPanningThumbBackgroundColor" ResourceKey="SystemChromeDisabledLowColor" />
+    <SolidColorBrush x:Key="ScrollBarThumbBackground" Color="{StaticResource ScrollBarThumbBackgroundColor}" />
+    <SolidColorBrush x:Key="ScrollBarPanningThumbBackground" Color="{StaticResource ScrollBarPanningThumbBackgroundColor}" />
+    <x:TimeSpan x:Key="ScrollBarExpandDuration">00:00:00.1</x:TimeSpan>
+    <x:String x:Key="ScrollBarExpandBeginTime">00:00:00.40</x:String>
+    <x:String x:Key="ScrollBarContractBeginTime">00:00:02.00</x:String>
+    <x:String x:Key="ScrollBarContractDelay">00:00:02</x:String>
+    <x:String x:Key="ScrollBarContractDuration">00:00:00.1</x:String>
+    <x:String x:Key="ScrollBarContractFinalKeyframe">00:00:02.1</x:String>
+    <x:Double x:Key="ScrollBarSize">16</x:Double>
+    <x:Double x:Key="SmallScrollThumbScale">0.125</x:Double>
+    <x:Double x:Key="SmallScrollThumbOffset">-2</x:Double>
+    <TransformOperations x:Key="VerticalSmallScrollThumbScaleTransform">scaleX(0.125) translateX(-2px)</TransformOperations>
+    <TransformOperations x:Key="HorizontalSmallScrollThumbScaleTransform">scaleY(0.125) translateY(-2px)</TransformOperations>
+    <x:Double x:Key="ScrollBarButtonArrowIconFontSize">8</x:Double>
+
+    <!-- BaseResources for ScrollViewer.xaml -->
+    <SolidColorBrush x:Key="ScrollViewerScrollBarsSeparatorBackground" Color="{StaticResource SystemChromeMediumColor}" Opacity="0.9" />
   </Style.Resources>
 </Style>

src/Avalonia.Themes.Fluent/Accents/FluentBaseLight.xaml

@@ -473,5 +473,56 @@
     <SolidColorBrush x:Key="PivotNavButtonPressedBackgroundThemeBrush" Color="#BD292929" />
     <SolidColorBrush x:Key="PivotNavButtonPressedBorderThemeBrush" Color="#BD292929" />
     <SolidColorBrush x:Key="PivotNavButtonPressedForegroundThemeBrush" Color="#FFFFFFFF" />
+
+    <!-- BaseResources for ScrollBar.xaml -->
+    <StaticResource x:Key="ScrollBarBackground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBackgroundPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBackgroundDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarForeground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrush" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrushPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrushDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundPointerOver" ResourceKey="SystemControlBackgroundListLowBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundPressed" ResourceKey="SystemControlBackgroundBaseMediumBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrush" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushPressed" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForeground" ResourceKey="SystemControlForegroundBaseHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundPointerOver" ResourceKey="SystemControlForegroundBaseHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundPressed" ResourceKey="SystemControlForegroundAltHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundDisabled" ResourceKey="SystemControlForegroundBaseLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFill" ResourceKey="SystemControlForegroundChromeDisabledLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillPointerOver" ResourceKey="SystemControlBackgroundBaseMediumLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillPressed" ResourceKey="SystemControlBackgroundBaseMediumBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <SolidColorBrush x:Key="ScrollBarTrackFill" Color="{StaticResource SystemChromeMediumColor}" Opacity="0.9" />
+    <SolidColorBrush x:Key="ScrollBarTrackFillPointerOver" Color="{StaticResource SystemChromeMediumColor}" Opacity="0.9" />
+    <StaticResource x:Key="ScrollBarTrackFillDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStroke" ResourceKey="SystemControlForegroundTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStrokePointerOver" ResourceKey="SystemControlForegroundTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStrokeDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <StaticResource x:Key="ScrollBarPanningThumbBackgroundDisabled" ResourceKey="SystemControlDisabledChromeHighBrush" />
+    <StaticResource x:Key="ScrollBarThumbBackgroundColor" ResourceKey="SystemBaseLowColor" />
+    <StaticResource x:Key="ScrollBarPanningThumbBackgroundColor" ResourceKey="SystemChromeDisabledLowColor" />
+    <SolidColorBrush x:Key="ScrollBarThumbBackground" Color="{StaticResource ScrollBarThumbBackgroundColor}" />
+    <SolidColorBrush x:Key="ScrollBarPanningThumbBackground" Color="{StaticResource ScrollBarPanningThumbBackgroundColor}" />
+    <x:String x:Key="ScrollBarExpandDuration">00:00:00.1</x:String>
+    <x:String x:Key="ScrollBarExpandBeginTime">00:00:00.40</x:String>
+    <x:String x:Key="ScrollBarContractBeginTime">00:00:02.00</x:String>
+    <x:String x:Key="ScrollBarContractDelay">00:00:02</x:String>
+    <x:String x:Key="ScrollBarContractDuration">00:00:00.1</x:String>
+    <x:String x:Key="ScrollBarContractFinalKeyframe">00:00:02.1</x:String>
+    <x:Double x:Key="ScrollBarSize">16</x:Double>
+    <x:Double x:Key="SmallScrollThumbScale">0.125</x:Double>
+    <x:Double x:Key="SmallScrollThumbOffset">-2</x:Double>
+    <TransformOperations x:Key="VerticalSmallScrollThumbScaleTransform">scaleX(0.125) translateX(-2px)</TransformOperations>
+    <TransformOperations x:Key="HorizontalSmallScrollThumbScaleTransform">scaleY(0.125) translateY(-2px)</TransformOperations>
+    <x:Double x:Key="ScrollBarButtonArrowIconFontSize">8</x:Double>
+
+    <!-- BaseResources for ScrollViewer.xaml -->
+    <SolidColorBrush x:Key="ScrollViewerScrollBarsSeparatorBackground" Color="{StaticResource SystemChromeMediumColor}" Opacity="0.9" />
   </Style.Resources>
 </Style>

src/Avalonia.Themes.Fluent/Accents/FluentControlResourcesDark.xaml

@@ -789,5 +789,98 @@
     <SolidColorBrush x:Key="PivotNavButtonPressedBackgroundThemeBrush" Color="#BD292929" />
     <SolidColorBrush x:Key="PivotNavButtonPressedBorderThemeBrush" Color="#BD292929" />
     <SolidColorBrush x:Key="PivotNavButtonPressedForegroundThemeBrush" Color="#FFFFFFFF" />
+
+    <!-- Resources for ScrollBar.xaml -->
+    <x:Double x:Key="ScrollBarTrackBorderThemeThickness">0</x:Double>
+    <Thickness x:Key="ScrollBarPanningBorderThemeThickness">1</Thickness>
+    <StaticResource x:Key="ScrollBarBackground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBackgroundPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBackgroundDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarForeground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrush" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrushPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrushDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundPointerOver" ResourceKey="SystemControlBackgroundListLowBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundPressed" ResourceKey="SystemControlBackgroundBaseMediumBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrush" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushPressed" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForeground" ResourceKey="SystemControlForegroundBaseHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundPointerOver" ResourceKey="SystemControlForegroundBaseHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundPressed" ResourceKey="SystemControlForegroundAltHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundDisabled" ResourceKey="SystemControlForegroundBaseLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFill" ResourceKey="SystemControlForegroundChromeDisabledLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillPointerOver" ResourceKey="SystemControlBackgroundBaseMediumLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillPressed" ResourceKey="SystemControlBackgroundBaseMediumBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <SolidColorBrush x:Key="ScrollBarTrackFill" Color="{StaticResource SystemChromeMediumColor}" Opacity="0.9" />
+    <SolidColorBrush x:Key="ScrollBarTrackFillPointerOver" Color="{StaticResource SystemChromeMediumColor}" Opacity="0.9" />
+    <StaticResource x:Key="ScrollBarTrackFillDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStroke" ResourceKey="SystemControlForegroundTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStrokePointerOver" ResourceKey="SystemControlForegroundTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStrokeDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <StaticResource x:Key="ScrollBarThumbBackgroundColor" ResourceKey="SystemBaseLowColor" />
+    <StaticResource x:Key="ScrollBarPanningThumbBackgroundColor" ResourceKey="SystemChromeDisabledLowColor" />
+    <SolidColorBrush x:Key="ScrollBarThumbBackground" Color="{StaticResource ScrollBarThumbBackgroundColor}" />
+    <SolidColorBrush x:Key="ScrollBarPanningThumbBackground" Color="{StaticResource ScrollBarPanningThumbBackgroundColor}" />
+    <StaticResource x:Key="ScrollBarPanningThumbBackgroundDisabled" ResourceKey="SystemControlDisabledChromeHighBrush" />
+    <SolidColorBrush x:Key="ScrollBarButtonForegroundThemeBrush" Color="#99000000" />
+    <SolidColorBrush x:Key="ScrollBarButtonPointerOverBackgroundThemeBrush" Color="#FFDADADA" />
+    <SolidColorBrush x:Key="ScrollBarButtonPointerOverBorderThemeBrush" Color="#FFDADADA" />
+    <SolidColorBrush x:Key="ScrollBarButtonPointerOverForegroundThemeBrush" Color="#FF000000" />
+    <SolidColorBrush x:Key="ScrollBarButtonPressedBackgroundThemeBrush" Color="#99000000" />
+    <SolidColorBrush x:Key="ScrollBarButtonPressedBorderThemeBrush" Color="#99000000" />
+    <SolidColorBrush x:Key="ScrollBarButtonPressedForegroundThemeBrush" Color="#FFFFFFFF" />
+    <SolidColorBrush x:Key="ScrollBarPanningBackgroundThemeBrush" Color="#FFCDCDCD" />
+    <SolidColorBrush x:Key="ScrollBarPanningBorderThemeBrush" Color="#7D9A9A9A" />
+    <SolidColorBrush x:Key="ScrollBarThumbBackgroundThemeBrush" Color="#FFCDCDCD" />
+    <SolidColorBrush x:Key="ScrollBarThumbBorderThemeBrush" Color="#3B555555" />
+    <SolidColorBrush x:Key="ScrollBarThumbPointerOverBackgroundThemeBrush" Color="#FFDADADA" />
+    <SolidColorBrush x:Key="ScrollBarThumbPointerOverBorderThemeBrush" Color="#6BB7B7B7" />
+    <SolidColorBrush x:Key="ScrollBarThumbPressedBackgroundThemeBrush" Color="#99000000" />
+    <SolidColorBrush x:Key="ScrollBarThumbPressedBorderThemeBrush" Color="#ED555555" />
+    <SolidColorBrush x:Key="ScrollBarTrackBackgroundThemeBrush" Color="#59D5D5D5" />
+    <SolidColorBrush x:Key="ScrollBarTrackBorderThemeBrush" Color="#59D5D5D5" />
+    <x:String x:Key="ScrollBarExpandDuration">00:00:00.1</x:String>
+    <x:String x:Key="ScrollBarContractDelay">00:00:02</x:String>
+    <x:String x:Key="ScrollBarContractDuration">00:00:00.1</x:String>
+    <x:String x:Key="ScrollBarContractFinalKeyframe">00:00:02.1</x:String>
+    <x:Double x:Key="ScrollBarSize">16</x:Double>
+    <x:Double x:Key="ScrollBarButtonArrowIconFontSize">8</x:Double>
+    <x:String x:Key="ScrollBarExpandBeginTime">00:00:00.40</x:String>
+    <x:String x:Key="ScrollBarContractBeginTime">00:00:02.00</x:String>
+    <!-- Resources for TreeViewItem.xaml -->
+    <StaticResource x:Key="TreeViewItemBackground" ResourceKey="SystemControlTransparentRevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundPointerOver" ResourceKey="SystemControlHighlightListLowRevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundPressed" ResourceKey="SystemControlHighlightListMediumRevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundSelected" ResourceKey="SystemControlHighlightAccent3RevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundSelectedPointerOver" ResourceKey="SystemControlHighlightAccent2RevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundSelectedPressed" ResourceKey="SystemControlHighlightListMediumRevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundSelectedDisabled" ResourceKey="SystemControlDisabledBaseMediumLowBrush" />
+    <StaticResource x:Key="TreeViewItemForeground" ResourceKey="SystemControlForegroundBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundPointerOver" ResourceKey="SystemControlHighlightAltBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundPressed" ResourceKey="SystemControlHighlightAltBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundDisabled" ResourceKey="SystemControlDisabledBaseMediumLowBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundSelected" ResourceKey="SystemControlHighlightAltBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundSelectedPointerOver" ResourceKey="SystemControlHighlightAltBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundSelectedPressed" ResourceKey="SystemControlHighlightAltBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundSelectedDisabled" ResourceKey="SystemControlDisabledBaseMediumLowBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrush" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushPointerOver" ResourceKey="SystemControlHighlightAltTransparentRevealBorderBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushPressed" ResourceKey="SystemControlHighlightAltTransparentRevealBorderBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushSelected" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushSelectedPointerOver" ResourceKey="SystemControlBackgroundTransparentRevealBorderBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushSelectedPressed" ResourceKey="SystemControlBackgroundTransparentRevealBorderBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushSelectedDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemCheckBoxBackgroundSelected" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemCheckBoxBorderSelected" ResourceKey="SystemControlForegroundBaseMediumHighBrush" />
+    <StaticResource x:Key="TreeViewItemCheckGlyphSelected" ResourceKey="SystemControlForegroundBaseMediumHighBrush" />
+    <Thickness x:Key="TreeViewItemBorderThemeThickness">1</Thickness>
+    <x:Double x:Key="TreeViewItemMinHeight">32</x:Double>
   </Style.Resources>
 </Style>

src/Avalonia.Themes.Fluent/Accents/FluentControlResourcesLight.xaml

@@ -366,8 +366,8 @@
     <x:Double x:Key="AutoCompleteBoxIconFontSize">12</x:Double>
 
     <!-- Resources for CheckBox.xaml -->
-    <x:Double x:Key="CheckBoxBorderThemeThickness">1</x:Double>
-    <x:Double x:Key="CheckBoxCheckedStrokeThickness">0</x:Double>
+    <Thickness x:Key="CheckBoxBorderThemeThickness">1</Thickness>
+    <Thickness x:Key="CheckBoxCheckedStrokeThickness">0</Thickness>
     <StaticResource x:Key="CheckBoxForegroundUnchecked" ResourceKey="SystemControlForegroundBaseHighBrush" />
     <StaticResource x:Key="CheckBoxForegroundUncheckedPointerOver" ResourceKey="SystemControlForegroundBaseHighBrush" />
     <StaticResource x:Key="CheckBoxForegroundUncheckedPressed" ResourceKey="SystemControlForegroundBaseHighBrush" />
@@ -787,5 +787,98 @@
     <SolidColorBrush x:Key="PivotNavButtonPressedBackgroundThemeBrush" Color="#BD292929" />
     <SolidColorBrush x:Key="PivotNavButtonPressedBorderThemeBrush" Color="#BD292929" />
     <SolidColorBrush x:Key="PivotNavButtonPressedForegroundThemeBrush" Color="#FFFFFFFF" />
+
+    <!-- Resources for ScrollBar.xaml -->
+    <x:Double x:Key="ScrollBarTrackBorderThemeThickness">0</x:Double>
+    <Thickness x:Key="ScrollBarPanningBorderThemeThickness">1</Thickness>
+    <StaticResource x:Key="ScrollBarBackground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBackgroundPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBackgroundDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarForeground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrush" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrushPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarBorderBrushDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackground" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundPointerOver" ResourceKey="SystemControlBackgroundListLowBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundPressed" ResourceKey="SystemControlBackgroundBaseMediumBrush" />
+    <StaticResource x:Key="ScrollBarButtonBackgroundDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrush" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushPointerOver" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushPressed" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonBorderBrushDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForeground" ResourceKey="SystemControlForegroundBaseHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundPointerOver" ResourceKey="SystemControlForegroundBaseHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundPressed" ResourceKey="SystemControlForegroundAltHighBrush" />
+    <StaticResource x:Key="ScrollBarButtonArrowForegroundDisabled" ResourceKey="SystemControlForegroundBaseLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFill" ResourceKey="SystemControlForegroundChromeDisabledLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillPointerOver" ResourceKey="SystemControlBackgroundBaseMediumLowBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillPressed" ResourceKey="SystemControlBackgroundBaseMediumBrush" />
+    <StaticResource x:Key="ScrollBarThumbFillDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <SolidColorBrush x:Key="ScrollBarTrackFill" Color="{StaticResource SystemChromeMediumColor}" Opacity="0.9" />
+    <SolidColorBrush x:Key="ScrollBarTrackFillPointerOver" Color="{StaticResource SystemChromeMediumColor}" Opacity="0.9" />
+    <StaticResource x:Key="ScrollBarTrackFillDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStroke" ResourceKey="SystemControlForegroundTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStrokePointerOver" ResourceKey="SystemControlForegroundTransparentBrush" />
+    <StaticResource x:Key="ScrollBarTrackStrokeDisabled" ResourceKey="SystemControlDisabledTransparentBrush" />
+    <SolidColorBrush x:Key="ScrollBarThumbBackground" Color="{StaticResource ScrollBarThumbBackgroundColor}" />
+    <SolidColorBrush x:Key="ScrollBarPanningThumbBackground" Color="{StaticResource ScrollBarPanningThumbBackgroundColor}" />
+    <StaticResource x:Key="ScrollBarPanningThumbBackgroundDisabled" ResourceKey="SystemControlDisabledChromeHighBrush" />
+    <SolidColorBrush x:Key="ScrollBarButtonForegroundThemeBrush" Color="#99000000" />
+    <SolidColorBrush x:Key="ScrollBarButtonPointerOverBackgroundThemeBrush" Color="#FFDADADA" />
+    <SolidColorBrush x:Key="ScrollBarButtonPointerOverBorderThemeBrush" Color="#FFDADADA" />
+    <SolidColorBrush x:Key="ScrollBarButtonPointerOverForegroundThemeBrush" Color="#FF000000" />
+    <SolidColorBrush x:Key="ScrollBarButtonPressedBackgroundThemeBrush" Color="#99000000" />
+    <SolidColorBrush x:Key="ScrollBarButtonPressedBorderThemeBrush" Color="#99000000" />
+    <SolidColorBrush x:Key="ScrollBarButtonPressedForegroundThemeBrush" Color="#FFFFFFFF" />
+    <SolidColorBrush x:Key="ScrollBarPanningBackgroundThemeBrush" Color="#FFCDCDCD" />
+    <SolidColorBrush x:Key="ScrollBarPanningBorderThemeBrush" Color="#7D9A9A9A" />
+    <SolidColorBrush x:Key="ScrollBarThumbBackgroundThemeBrush" Color="#FFCDCDCD" />
+    <SolidColorBrush x:Key="ScrollBarThumbBorderThemeBrush" Color="#3B555555" />
+    <SolidColorBrush x:Key="ScrollBarThumbPointerOverBackgroundThemeBrush" Color="#FFDADADA" />
+    <SolidColorBrush x:Key="ScrollBarThumbPointerOverBorderThemeBrush" Color="#6BB7B7B7" />
+    <SolidColorBrush x:Key="ScrollBarThumbPressedBackgroundThemeBrush" Color="#99000000" />
+    <SolidColorBrush x:Key="ScrollBarThumbPressedBorderThemeBrush" Color="#ED555555" />
+    <SolidColorBrush x:Key="ScrollBarTrackBackgroundThemeBrush" Color="#59D5D5D5" />
+    <SolidColorBrush x:Key="ScrollBarTrackBorderThemeBrush" Color="#59D5D5D5" />
+    <StaticResource x:Key="ScrollBarThumbBackgroundColor" ResourceKey="SystemBaseLowColor" />
+    <StaticResource x:Key="ScrollBarPanningThumbBackgroundColor" ResourceKey="SystemChromeDisabledLowColor" />
+    <x:String x:Key="ScrollBarExpandDuration">00:00:00.1</x:String>
+    <x:String x:Key="ScrollBarContractDelay">00:00:02</x:String>
+    <x:String x:Key="ScrollBarContractDuration">00:00:00.1</x:String>
+    <x:String x:Key="ScrollBarContractFinalKeyframe">00:00:02.1</x:String>
+    <x:Double x:Key="ScrollBarSize">16</x:Double>
+    <x:Double x:Key="ScrollBarButtonArrowIconFontSize">8</x:Double>
+    <x:String x:Key="ScrollBarExpandBeginTime">00:00:00.40</x:String>
+    <x:String x:Key="ScrollBarContractBeginTime">00:00:02.00</x:String>
+    <!-- Resources for TreeViewItem.xaml -->
+    <StaticResource x:Key="TreeViewItemBackground" ResourceKey="SystemControlTransparentRevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundPointerOver" ResourceKey="SystemControlHighlightListLowRevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundPressed" ResourceKey="SystemControlHighlightListMediumRevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundSelected" ResourceKey="SystemControlHighlightAccent3RevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundSelectedPointerOver" ResourceKey="SystemControlHighlightAccent2RevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundSelectedPressed" ResourceKey="SystemControlHighlightListMediumRevealBackgroundBrush" />
+    <StaticResource x:Key="TreeViewItemBackgroundSelectedDisabled" ResourceKey="SystemControlDisabledBaseMediumLowBrush" />
+    <StaticResource x:Key="TreeViewItemForeground" ResourceKey="SystemControlForegroundBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundPointerOver" ResourceKey="SystemControlHighlightAltBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundPressed" ResourceKey="SystemControlHighlightAltBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundDisabled" ResourceKey="SystemControlDisabledBaseMediumLowBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundSelected" ResourceKey="SystemControlHighlightAltBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundSelectedPointerOver" ResourceKey="SystemControlHighlightAltBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundSelectedPressed" ResourceKey="SystemControlHighlightAltBaseHighBrush" />
+    <StaticResource x:Key="TreeViewItemForegroundSelectedDisabled" ResourceKey="SystemControlDisabledBaseMediumLowBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrush" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushPointerOver" ResourceKey="SystemControlHighlightAltTransparentRevealBorderBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushPressed" ResourceKey="SystemControlHighlightAltTransparentRevealBorderBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushSelected" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushSelectedPointerOver" ResourceKey="SystemControlBackgroundTransparentRevealBorderBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushSelectedPressed" ResourceKey="SystemControlBackgroundTransparentRevealBorderBrush" />
+    <StaticResource x:Key="TreeViewItemBorderBrushSelectedDisabled" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemCheckBoxBackgroundSelected" ResourceKey="SystemControlTransparentBrush" />
+    <StaticResource x:Key="TreeViewItemCheckBoxBorderSelected" ResourceKey="SystemControlForegroundBaseMediumHighBrush" />
+    <StaticResource x:Key="TreeViewItemCheckGlyphSelected" ResourceKey="SystemControlForegroundBaseMediumHighBrush" />
+    <Thickness x:Key="TreeViewItemBorderThemeThickness">1</Thickness>
+    <x:Double x:Key="TreeViewItemMinHeight">32</x:Double>
   </Style.Resources>
 </Style>

src/Avalonia.Themes.Fluent/ScrollBar.xaml

@@ -1,142 +1,302 @@
-<Styles xmlns="https://github.com/avaloniaui">
+<Styles xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+
   <Style Selector="ScrollBar">
-    <Setter Property="Cursor" Value="Arrow" />
+    <Setter Property="MinWidth" Value="{DynamicResource ScrollBarSize}" />
+    <Setter Property="MinHeight" Value="{DynamicResource ScrollBarSize}" />
+    <Setter Property="Background" Value="{DynamicResource ScrollBarBackground}" />
+    <Setter Property="Foreground" Value="{DynamicResource ScrollBarForeground}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource ScrollBarBorderBrush}" />
+  </Style>
+
+  <Style Selector="ScrollBar:vertical">
     <Setter Property="Template">
       <ControlTemplate>
-        <Border Background="{DynamicResource ThemeControlMidBrush}"
-                UseLayoutRounding="False">
-          <Grid RowDefinitions="Auto,*,Auto">
-            <RepeatButton Name="PART_LineUpButton" HorizontalAlignment="Center"
-                          Classes="repeat"
-                          Grid.Row="0"
-                          Focusable="False"
-                          MinHeight="{DynamicResource ScrollBarThickness}">
-              <Path Data="M 0 4 L 8 4 L 4 0 Z" />
-            </RepeatButton>
-            <Track Grid.Row="1"
-                   Grid.Column="1"
-                   Minimum="{TemplateBinding Minimum}"
-                   Maximum="{TemplateBinding Maximum}"
-                   Value="{TemplateBinding Value, Mode=TwoWay}"
-                   ViewportSize="{TemplateBinding ViewportSize}"
-                   Orientation="{TemplateBinding Orientation}"
-                   IsDirectionReversed="True">
-              <Track.DecreaseButton>
-                <RepeatButton Name="PART_PageUpButton"
-                              Classes="repeattrack"
-                              Focusable="False"/>
-              </Track.DecreaseButton>
-              <Track.IncreaseButton>
-                <RepeatButton Name="PART_PageDownButton"
-                              Classes="repeattrack"
-                              Focusable="False"/>
-              </Track.IncreaseButton>
-              <Thumb Name="thumb"/>
-            </Track>
-            <RepeatButton Name="PART_LineDownButton" HorizontalAlignment="Center"
-                          Classes="repeat"
-                          Grid.Row="2"
-                          Grid.Column="2"
-                          Focusable="False"
-                          MinHeight="{DynamicResource ScrollBarThickness}">
-              <Path Data="M 0 0 L 4 4 L 8 0 Z" />
-            </RepeatButton>
-          </Grid>
-        </Border>
+        <Grid x:Name="Root">
+
+          <Border x:Name="VerticalRoot"
+                  Background="{TemplateBinding Background}"
+                  BorderBrush="{TemplateBinding BorderBrush}">
+            <Grid RowDefinitions="Auto,*,Auto">
+
+              <Rectangle x:Name="TrackRect" Grid.RowSpan="3" Margin="0" />
+
+              <RepeatButton Name="PART_LineUpButton"
+                            HorizontalAlignment="Center"
+                            Classes="line up"
+                            Grid.Row="0"
+                            Focusable="False"
+                            MinWidth="{DynamicResource ScrollBarSize}"
+                            Height="{DynamicResource ScrollBarSize}" />
+
+              <Track Grid.Row="1"
+                     Minimum="{TemplateBinding Minimum}"
+                     Maximum="{TemplateBinding Maximum}"
+                     Value="{TemplateBinding Value, Mode=TwoWay}"
+                     ViewportSize="{TemplateBinding ViewportSize}"
+                     Orientation="{TemplateBinding Orientation}"
+                     IsDirectionReversed="True">
+                <Track.DecreaseButton>
+                  <RepeatButton Name="PART_PageUpButton"
+                                Classes="largeIncrease"
+                                Focusable="False" />
+                </Track.DecreaseButton>
+                <Track.IncreaseButton>
+                  <RepeatButton Name="PART_PageDownButton"
+                                Classes="largeIncrease"
+                                Focusable="False" />
+                </Track.IncreaseButton>
+                <Thumb Classes="thumb"
+                       Opacity="1"
+                       Width="{DynamicResource ScrollBarSize}"
+                       MinHeight="{DynamicResource ScrollBarSize}"
+                       RenderTransformOrigin="100%,50%" />
+              </Track>
+
+              <RepeatButton Name="PART_LineDownButton"
+                            HorizontalAlignment="Center"
+                            Classes="line down"
+                            Grid.Row="2"
+                            Focusable="False"
+                            MinWidth="{DynamicResource ScrollBarSize}"
+                            Height="{DynamicResource ScrollBarSize}" />
+
+            </Grid>
+          </Border>
+
+        </Grid>
       </ControlTemplate>
     </Setter>
   </Style>
+
   <Style Selector="ScrollBar:horizontal">
-    <Setter Property="Height" Value="{DynamicResource ScrollBarThickness}" />
     <Setter Property="Template">
       <ControlTemplate>
-        <Border Background="{DynamicResource ThemeControlMidBrush}"
-                UseLayoutRounding="False">
-          <Grid ColumnDefinitions="Auto,*,Auto">
-            <RepeatButton Name="PART_LineUpButton" VerticalAlignment="Center"
-                          Classes="repeat"
-                          Grid.Row="0"
-                          Grid.Column="0"
-                          Focusable="False"
-                          MinWidth="{DynamicResource ScrollBarThickness}">
-              <Path Data="M 4 0 L 4 8 L 0 4 Z" />
-            </RepeatButton>
-            <Track Grid.Row="1"
-                   Grid.Column="1"
-                   Minimum="{TemplateBinding Minimum}"
-                   Maximum="{TemplateBinding Maximum}"
-                   Value="{TemplateBinding Value, Mode=TwoWay}"
-                   ViewportSize="{TemplateBinding ViewportSize}"
-                   Orientation="{TemplateBinding Orientation}">
-              <Track.DecreaseButton>
-                <RepeatButton Name="PART_PageUpButton"
-                              Classes="repeattrack"
-                              Focusable="False"/>
-              </Track.DecreaseButton>
-              <Track.IncreaseButton>
-                <RepeatButton Name="PART_PageDownButton"
-                              Classes="repeattrack"
-                              Focusable="False"/>
-              </Track.IncreaseButton>
-              <Thumb Name="thumb"/>
-            </Track>
-            <RepeatButton Name="PART_LineDownButton" VerticalAlignment="Center"
-                          Classes="repeat"
-                          Grid.Row="2"
-                          Grid.Column="2"
-                          Focusable="False"
-                          MinWidth="{DynamicResource ScrollBarThickness}">
-              <Path Data="M 0 0 L 4 4 L 0 8 Z"  />
-            </RepeatButton>
-          </Grid>
-        </Border>
+        <Grid x:Name="Root">
+
+          <Border x:Name="HorizontalRoot"
+                  Background="{TemplateBinding Background}"
+                  BorderBrush="{TemplateBinding BorderBrush}">
+            <Grid ColumnDefinitions="Auto,*,Auto">
+
+              <Rectangle x:Name="TrackRect" Grid.ColumnSpan="3" Margin="0" />
+
+              <RepeatButton Name="PART_LineUpButton"
+                            VerticalAlignment="Center"
+                            Classes="line up"
+                            Grid.Column="0"
+                            Focusable="False"
+                            MinHeight="{DynamicResource ScrollBarSize}"
+                            Width="{DynamicResource ScrollBarSize}" />
+
+              <Track Grid.Column="1"
+                     Minimum="{TemplateBinding Minimum}"
+                     Maximum="{TemplateBinding Maximum}"
+                     Value="{TemplateBinding Value, Mode=TwoWay}"
+                     ViewportSize="{TemplateBinding ViewportSize}"
+                     Orientation="{TemplateBinding Orientation}">
+                <Track.DecreaseButton>
+                  <RepeatButton Name="PART_PageUpButton"
+                                Classes="largeIncrease"
+                                Focusable="False" />
+                </Track.DecreaseButton>
+                <Track.IncreaseButton>
+                  <RepeatButton Name="PART_PageDownButton"
+                                Classes="largeIncrease"
+                                Focusable="False" />
+                </Track.IncreaseButton>
+                <Thumb Classes="thumb"
+                       Opacity="1"
+                       Height="{DynamicResource ScrollBarSize}"
+                       MinWidth="{DynamicResource ScrollBarSize}"
+                       RenderTransformOrigin="50%,100%" />
+              </Track>
+
+              <RepeatButton Name="PART_LineDownButton"
+                            VerticalAlignment="Center"
+                            Classes="line down"
+                            Grid.Column="2"
+                            Focusable="False"
+                            MinHeight="{DynamicResource ScrollBarSize}"
+                            Width="{DynamicResource ScrollBarSize}" />
+
+            </Grid>
+          </Border>
+
+        </Grid>
       </ControlTemplate>
     </Setter>
   </Style>
-  <Style Selector="ScrollBar /template/ Thumb#thumb">
-    <Setter Property="Background" Value="{DynamicResource ThemeControlMidHighBrush}"/>
+
+  <Style Selector="ScrollBar[IsExpanded=true] /template/ Grid#Root">
+    <Setter Property="Background" Value="{DynamicResource ScrollBarBackgroundPointerOver}" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ Thumb.thumb">
+    <Setter Property="Background" Value="{DynamicResource ScrollBarPanningThumbBackground}" />
     <Setter Property="Template">
       <Setter.Value>
         <ControlTemplate>
-          <Border Background="{TemplateBinding Background}"/>
+          <Border x:Name="ThumbVisual" Background="{TemplateBinding Background}" />
         </ControlTemplate>
       </Setter.Value>
     </Setter>
+    <Setter Property="Transitions">
+      <Transitions>
+        <TransformOperationsTransition Property="RenderTransform" Duration="0:0:0.1" />
+      </Transitions>
+    </Setter>
   </Style>
-  <Style Selector="ScrollBar /template/ Thumb#thumb:pointerover">
-    <Setter Property="Background" Value="{DynamicResource ThemeControlHighBrush}"/>
+
+  <Style Selector="ScrollBar:vertical /template/ Thumb.thumb">
+    <Setter Property="RenderTransform" Value="{DynamicResource VerticalSmallScrollThumbScaleTransform}" />
   </Style>
-  <Style Selector="ScrollBar /template/ Thumb#thumb:pressed">
-    <Setter Property="Background" Value="{DynamicResource ThemeControlVeryHighBrush}"/>
+
+  <Style Selector="ScrollBar:horizontal /template/ Thumb.thumb">
+    <Setter Property="RenderTransform" Value="{DynamicResource HorizontalSmallScrollThumbScaleTransform}" />
   </Style>
-  <Style Selector="ScrollBar:horizontal /template/ Thumb#thumb">
-    <Setter Property="MinWidth" Value="{DynamicResource ScrollBarThickness}" />
-    <Setter Property="Height" Value="{DynamicResource ScrollBarThumbThickness}" />
+
+  <Style Selector="ScrollBar[IsExpanded=true] /template/ Thumb.thumb">
+    <Setter Property="RenderTransform" Value="none" />
+    <Setter Property="Background" Value="{DynamicResource ScrollBarThumbBackgroundColor}" />
   </Style>
-  <Style Selector="ScrollBar:vertical">
-    <Setter Property="Width" Value="{DynamicResource ScrollBarThickness}" />
+
+  <Style Selector="ScrollBar /template/ Thumb.thumb /template/ Border#ThumbVisual">
+    <Setter Property="CornerRadius" Value="{DynamicResource ControlCornerRadius}" />
+    <Setter Property="Transitions">
+      <Transitions>
+        <CornerRadiusTransition Property="CornerRadius" Duration="0:0:0.1" />
+      </Transitions>
+    </Setter>
   </Style>
-  <Style Selector="ScrollBar:vertical /template/ Thumb#thumb">
-    <Setter Property="MinHeight" Value="{DynamicResource ScrollBarThickness}" />
-    <Setter Property="Width" Value="{DynamicResource ScrollBarThumbThickness}" />
+
+  <Style Selector="ScrollBar[IsExpanded=true] /template/ Thumb.thumb /template/ Border#ThumbVisual">
+    <Setter Property="CornerRadius" Value="0" />
   </Style>
-  <Style Selector="ScrollBar /template/ RepeatButton.repeat">
-    <Setter Property="Padding" Value="2" />
-    <Setter Property="BorderThickness" Value="0" />
+
+  <Style Selector="ScrollBar /template/ Thumb.thumb:pointerover">
+    <Setter Property="Background" Value="{DynamicResource ScrollBarThumbFillPointerOver}" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ Thumb.thumb:pressed">
+    <Setter Property="Background" Value="{DynamicResource ScrollBarThumbFillPressed}" />
   </Style>
-  <Style Selector="ScrollBar /template/ RepeatButton.repeattrack">
+
+  <Style Selector="ScrollBar /template/ Thumb.thumb:disabled">
+    <Setter Property="Background" Value="{DynamicResource ScrollBarThumbFillDisabled}" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ RepeatButton.line">
     <Setter Property="Template">
       <ControlTemplate>
-        <Border Background="{TemplateBinding Background}" />
+        <Border x:Name="Root">
+          <Viewbox Width="{DynamicResource ScrollBarButtonArrowIconFontSize}"
+                   Height="{DynamicResource ScrollBarButtonArrowIconFontSize}">
+            <Path x:Name="Arrow"
+              VerticalAlignment="Center"
+              HorizontalAlignment="Center"
+              Width="20" Height="20" />
+          </Viewbox>
+        </Border>
       </ControlTemplate>
     </Setter>
+    <Setter Property="Opacity" Value="0" />
+    <Setter Property="Transitions">
+      <Transitions>
+        <DoubleTransition Property="Opacity" Duration="0:0:0.1" />
+      </Transitions>
+    </Setter>
+  </Style>
+
+  <Style Selector="ScrollBar /template/ RepeatButton.line /template/ Border#Root" >
+    <Setter Property="Background" Value="{DynamicResource ScrollBarButtonBackground}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource ScrollBarButtonBorderBrush}" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ RepeatButton.line:pointerover /template/ Border#Root" >
+    <Setter Property="Background" Value="{DynamicResource ScrollBarButtonBackgroundPointerOver}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource ScrollBarButtonBorderBrushPointerOver}" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ RepeatButton.line:pressed /template/ Border#Root" >
+    <Setter Property="Background" Value="{DynamicResource ScrollBarButtonBackgroundPressed}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource ScrollBarButtonBorderBrushPressed}" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ RepeatButton.line:disabled /template/ Border#Root" >
+    <Setter Property="Background" Value="{DynamicResource ScrollBarButtonBackgroundPressed}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource ScrollBarButtonBorderBrushDisabled}" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ RepeatButton.line /template/ Path#Arrow" >
+    <Setter Property="Fill" Value="{DynamicResource ScrollBarButtonArrowForeground}" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ RepeatButton.line:pointerover /template/ Path#Arrow" >
+    <Setter Property="Fill" Value="{DynamicResource ScrollBarButtonArrowForegroundPointerOver}" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ RepeatButton.line:pressed /template/ Path#Arrow" >
+    <Setter Property="Fill" Value="{DynamicResource ScrollBarButtonArrowForegroundPressed}" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ RepeatButton.line:disabled /template/ Path#Arrow" >
+    <Setter Property="Fill" Value="{DynamicResource ScrollBarButtonArrowForegroundDisabled}" />
+  </Style>
+
+  <Style Selector="ScrollBar[IsExpanded=true] /template/ RepeatButton.line">
+    <Setter Property="Opacity" Value="1" />
   </Style>
 
-  <Style Selector="ScrollBar /template/ RepeatButton > Path">
-    <Setter Property="Fill" Value="{DynamicResource ThemeForegroundLowBrush}" />
+  <Style Selector="ScrollBar:vertical /template/ RepeatButton.line.up /template/ Path">
+    <Setter Property="Data"
+            Value="M 19.091797 14.970703 L 10 5.888672 L 0.908203 14.970703 L 0.029297 14.091797 L 10 4.111328 L 19.970703 14.091797 Z" />
   </Style>
 
-  <Style Selector="ScrollBar /template/ RepeatButton:pointerover > Path">
-    <Setter Property="Fill" Value="{DynamicResource ThemeAccentBrush}" />
+  <Style Selector="ScrollBar:vertical /template/ RepeatButton.line.down /template/ Path">
+    <Setter Property="Data"
+            Value="M 18.935547 4.560547 L 19.814453 5.439453 L 10 15.253906 L 0.185547 5.439453 L 1.064453 4.560547 L 10 13.496094 Z" />
   </Style>
+
+  <Style Selector="ScrollBar:horizontal /template/ RepeatButton.line.up /template/ Path">
+    <Setter Property="Data" Value="M 14.091797 19.970703 L 4.111328 10 L 14.091797 0.029297 L 14.970703 0.908203 L 5.888672 10 L 14.970703 19.091797 Z" />
+  </Style>
+
+  <Style Selector="ScrollBar:horizontal /template/ RepeatButton.line.down /template/ Path">
+    <Setter Property="Data" Value="M 5.029297 19.091797 L 14.111328 10 L 5.029297 0.908203 L 5.908203 0.029297 L 15.888672 10 L 5.908203 19.970703 Z" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ Rectangle#TrackRect">
+    <Setter Property="StrokeThickness" Value="{DynamicResource ScrollBarTrackBorderThemeThickness}" />
+    <Setter Property="Fill" Value="{DynamicResource ScrollBarTrackFill}" />
+    <Setter Property="Stroke" Value="{DynamicResource ScrollBarTrackStroke}" />
+    <Setter Property="Opacity" Value="0" />
+    <Setter Property="Transitions">
+      <Transitions>
+        <DoubleTransition Property="Opacity" Duration="0:0:0.1" />
+      </Transitions>
+    </Setter>
+  </Style>
+
+  <Style Selector="ScrollBar[IsExpanded=true] /template/ Rectangle#TrackRect">
+    <Setter Property="Fill" Value="{DynamicResource ScrollBarTrackFillPointerOver}" />
+    <Setter Property="Stroke" Value="{DynamicResource ScrollBarTrackStrokePointerOver}" />
+    <Setter Property="Opacity" Value="1" />
+  </Style>
+
+  <Style Selector="ScrollBar /template/ RepeatButton.largeIncrease">
+    <Setter Property="Template">
+      <ControlTemplate>
+        <Border Background="{TemplateBinding Background}" />
+      </ControlTemplate>
+    </Setter>
+    <Setter Property="Background" Value="Transparent" />
+    <Setter Property="VerticalAlignment" Value="Stretch" />
+    <Setter Property="HorizontalAlignment" Value="Stretch" />
+    <Setter Property="Opacity" Value="0" />
+  </Style>
+
+  <Style Selector="ScrollBar[IsExpanded=true] /template/ RepeatButton.largeIncrease">
+    <Setter Property="Opacity" Value="1" />
+  </Style>
+
 </Styles>

src/Avalonia.Themes.Fluent/ScrollViewer.xaml

@@ -1,47 +1,69 @@
-<Style xmlns="https://github.com/avaloniaui" Selector="ScrollViewer">
-  <Setter Property="Background"
-          Value="Transparent" />
-  <Setter Property="Template">
-    <ControlTemplate>
-      <Grid ColumnDefinitions="*,Auto" RowDefinitions="*,Auto">
-        <ScrollContentPresenter Name="PART_ContentPresenter"
-                                Background="{TemplateBinding Background}"
-                                CanHorizontallyScroll="{TemplateBinding CanHorizontallyScroll}"
-                                CanVerticallyScroll="{TemplateBinding CanVerticallyScroll}"
-                                Content="{TemplateBinding Content}"
-                                Extent="{TemplateBinding Extent, Mode=TwoWay}"
-                                Margin="{TemplateBinding Padding}"
-                                Offset="{TemplateBinding Offset, Mode=TwoWay}"
-                                Viewport="{TemplateBinding Viewport, Mode=TwoWay}">
-          <ScrollContentPresenter.GestureRecognizers>
-            <ScrollGestureRecognizer 
-              CanHorizontallyScroll="{TemplateBinding CanHorizontallyScroll}"
-              CanVerticallyScroll="{TemplateBinding CanVerticallyScroll}"
-            />
-          </ScrollContentPresenter.GestureRecognizers>  
-        </ScrollContentPresenter>
-        <ScrollBar Name="horizontalScrollBar"
-                   Orientation="Horizontal"
-                   LargeChange="{Binding LargeChange.Width, RelativeSource={RelativeSource TemplatedParent}}"
-                   SmallChange="{Binding SmallChange.Width, RelativeSource={RelativeSource TemplatedParent}}"
-                   Maximum="{TemplateBinding HorizontalScrollBarMaximum}"
-                   Value="{TemplateBinding HorizontalScrollBarValue, Mode=TwoWay}"
-                   ViewportSize="{TemplateBinding HorizontalScrollBarViewportSize}"
-                   Visibility="{TemplateBinding HorizontalScrollBarVisibility}"
-                   Grid.Row="1"
-                   Focusable="False"/>
-        <ScrollBar Name="verticalScrollBar"
-                   Orientation="Vertical"
-                   LargeChange="{Binding LargeChange.Height, RelativeSource={RelativeSource TemplatedParent}}"
-                   SmallChange="{Binding SmallChange.Height, RelativeSource={RelativeSource TemplatedParent}}"
-                   Maximum="{TemplateBinding VerticalScrollBarMaximum}"
-                   Value="{TemplateBinding VerticalScrollBarValue, Mode=TwoWay}"
-                   ViewportSize="{TemplateBinding VerticalScrollBarViewportSize}"
-                   Visibility="{TemplateBinding VerticalScrollBarVisibility}"
-                   Grid.Column="1"
-                   Focusable="False"/>
-        <Panel Grid.Row="1" Grid.Column="1" Background="{DynamicResource ThemeControlMidBrush}"/>
-      </Grid>
-    </ControlTemplate>
-  </Setter>
-</Style>
+<Styles xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+
+  <Style Selector="ScrollViewer">
+    <Setter Property="Background"
+            Value="Transparent" />
+    <Setter Property="Template">
+      <ControlTemplate>
+        <Grid ColumnDefinitions="*,Auto" RowDefinitions="*,Auto">
+          <ScrollContentPresenter Name="PART_ContentPresenter"
+                                  Grid.Row="0"
+                                  Grid.Column="0"
+                                  Grid.RowSpan="2"
+                                  Grid.ColumnSpan="2"
+                                  Background="{TemplateBinding Background}"
+                                  CanHorizontallyScroll="{TemplateBinding CanHorizontallyScroll}"
+                                  CanVerticallyScroll="{TemplateBinding CanVerticallyScroll}"
+                                  Content="{TemplateBinding Content}"
+                                  Extent="{TemplateBinding Extent, Mode=TwoWay}"
+                                  Margin="{TemplateBinding Padding}"
+                                  Offset="{TemplateBinding Offset, Mode=TwoWay}"
+                                  Viewport="{TemplateBinding Viewport, Mode=TwoWay}">
+            <ScrollContentPresenter.GestureRecognizers>
+              <ScrollGestureRecognizer
+                CanHorizontallyScroll="{TemplateBinding CanHorizontallyScroll}"
+                CanVerticallyScroll="{TemplateBinding CanVerticallyScroll}" />
+            </ScrollContentPresenter.GestureRecognizers>
+          </ScrollContentPresenter>
+          <ScrollBar Name="PART_HorizontalScrollBar"
+                     AllowAutoHide="{TemplateBinding AllowAutoHide}"
+                     Orientation="Horizontal"
+                     LargeChange="{Binding LargeChange.Width, RelativeSource={RelativeSource TemplatedParent}}"
+                     SmallChange="{Binding SmallChange.Width, RelativeSource={RelativeSource TemplatedParent}}"
+                     Maximum="{TemplateBinding HorizontalScrollBarMaximum}"
+                     Value="{TemplateBinding HorizontalScrollBarValue, Mode=TwoWay}"
+                     ViewportSize="{TemplateBinding HorizontalScrollBarViewportSize}"
+                     Visibility="{TemplateBinding HorizontalScrollBarVisibility}"
+                     Grid.Row="1"
+                     Focusable="False" />
+          <ScrollBar Name="PART_VerticalScrollBar"
+                     AllowAutoHide="{TemplateBinding AllowAutoHide}"
+                     Orientation="Vertical"
+                     LargeChange="{Binding LargeChange.Height, RelativeSource={RelativeSource TemplatedParent}}"
+                     SmallChange="{Binding SmallChange.Height, RelativeSource={RelativeSource TemplatedParent}}"
+                     Maximum="{TemplateBinding VerticalScrollBarMaximum}"
+                     Value="{TemplateBinding VerticalScrollBarValue, Mode=TwoWay}"
+                     ViewportSize="{TemplateBinding VerticalScrollBarViewportSize}"
+                     Visibility="{TemplateBinding VerticalScrollBarVisibility}"
+                     Grid.Column="1"
+                     Focusable="False" />
+          <Panel x:Name="PART_ScrollBarsSeparator" Grid.Row="1" Grid.Column="1" Background="{DynamicResource ScrollViewerScrollBarsSeparatorBackground}" />
+        </Grid>
+      </ControlTemplate>
+    </Setter>
+  </Style>
+
+  <Style Selector="ScrollViewer /template/ Panel#PART_ScrollBarsSeparator">
+    <Setter Property="Opacity" Value="0" />
+    <Setter Property="Transitions">
+      <Transitions>
+        <DoubleTransition Property="Opacity" Duration="0:0:0.1" />
+      </Transitions>
+    </Setter>
+  </Style>
+
+  <Style Selector="ScrollViewer[IsExpanded=true] /template/ Panel#PART_ScrollBarsSeparator">
+    <Setter Property="Opacity" Value="1" />
+  </Style>
+
+</Styles>

src/Avalonia.Themes.Fluent/ToggleSwitch.xaml

@@ -3,8 +3,8 @@
         xmlns:sys="clr-namespace:System;assembly=netstandard">
   <Styles.Resources>
     <Thickness x:Key="ToggleSwitchTopHeaderMargin">0,0,0,6</Thickness>
-    <x:Double x:Key="ToggleSwitchPreContentMargin">6</x:Double>
-    <x:Double x:Key="ToggleSwitchPostContentMargin">6</x:Double>
+    <GridLength x:Key="ToggleSwitchPreContentMargin">6</GridLength>
+    <GridLength x:Key="ToggleSwitchPostContentMargin">6</GridLength>
     <x:Double x:Key="ToggleSwitchThemeMinWidth">154</x:Double>
     <x:Double x:Key="KnobOnPosition">20</x:Double>
     <x:Double x:Key="KnobOffPosition">0</x:Double>

src/Avalonia.Themes.Fluent/TreeView.xaml

@@ -1,10 +1,11 @@
-<Style xmlns="https://github.com/avaloniaui" Selector="TreeView">
-  <Setter Property="Background" Value="Transparent"/>
-  <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderMidBrush}"/>
-  <Setter Property="BorderThickness" Value="{DynamicResource ThemeBorderThickness}"/>
-  <Setter Property="Padding" Value="4"/>
-  <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
-  <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"/>
+<Style xmlns="https://github.com/avaloniaui"
+       Selector="TreeView">
+  <Setter Property="Background" Value="Transparent" />
+  <Setter Property="BorderBrush" Value="Transparent" />
+  <Setter Property="BorderThickness" Value="0" />
+  <Setter Property="Padding" Value="0" />
+  <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto" />
+  <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto" />
   <Setter Property="Template">
     <ControlTemplate>
       <Border BorderBrush="{TemplateBinding BorderBrush}"
@@ -15,7 +16,7 @@
           <ItemsPresenter Name="PART_ItemsPresenter"
                           Items="{TemplateBinding Items}"
                           ItemsPanel="{TemplateBinding ItemsPanel}"
-                          Margin="{TemplateBinding Padding}"/>
+                          Margin="{TemplateBinding Padding}" />
         </ScrollViewer>
       </Border>
     </ControlTemplate>

src/Avalonia.Themes.Fluent/TreeViewItem.xaml

@@ -1,92 +1,180 @@
 <Styles xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:converters="clr-namespace:Avalonia.Controls.Converters;assembly=Avalonia.Controls">
-    <Style Selector="TreeViewItem">
-        <Style.Resources>
-            <converters:MarginMultiplierConverter Indent="16" Left="True" x:Key="LeftMarginConverter" />
-        </Style.Resources>
-        <Setter Property="Padding" Value="2"/>
-        <Setter Property="Background" Value="Transparent"/>
-        <Setter Property="Template">
-            <ControlTemplate>
-                <StackPanel>
-                    <Border Name="SelectionBorder"
-                            Focusable="True"
-                            Background="{TemplateBinding Background}"
-                            BorderBrush="{TemplateBinding BorderBrush}"
-                            BorderThickness="{TemplateBinding BorderThickness}"
-                            TemplatedControl.IsTemplateFocusTarget="True">
-                        <Grid Name="PART_Header"
-                              ColumnDefinitions="16, *"
-                              Margin="{TemplateBinding Level, Mode=OneWay, Converter={StaticResource LeftMarginConverter}}" >
-                            <ToggleButton Name="expander"
-                                          Focusable="False"
-                                          IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}"/>
-                            <ContentPresenter Name="PART_HeaderPresenter"
-                                              Focusable="False"
-                                              Content="{TemplateBinding Header}"
-                                              HorizontalContentAlignment="{TemplateBinding HorizontalAlignment}"
-                                              Padding="{TemplateBinding Padding}"
-                                              Grid.Column="1"/>
-                        </Grid>
-                    </Border>
-                    <ItemsPresenter Name="PART_ItemsPresenter"
-                                    IsVisible="{TemplateBinding IsExpanded}"
-                                    Items="{TemplateBinding Items}"
-                                    ItemsPanel="{TemplateBinding ItemsPanel}"/>
-                </StackPanel>
-            </ControlTemplate>
-        </Setter>
-    </Style>
 
-    <Style Selector="TreeViewItem /template/ ToggleButton#expander">
-        <Setter Property="Template">
-            <ControlTemplate>
-                <Border Background="Transparent"
-                        Width="14"
-                        Height="12"
-                        HorizontalAlignment="Center"
-                        VerticalAlignment="Center">
-                    <Path Fill="{DynamicResource ThemeForegroundBrush}"
-                          HorizontalAlignment="Center"
-                          VerticalAlignment="Center"
-                          Data="M 0 2 L 4 6 L 0 10 Z"/>
-                </Border>
-            </ControlTemplate>
-        </Setter>
-    </Style>
+  <Design.PreviewWith>
+    <Border Padding="20"
+            MinWidth="300">
+      <TreeView>
+        <TreeViewItem Header="Level 1">
+          <TreeViewItem Header="Level 2.1">
+            <TreeViewItem Header="Level 3.1" />
+            <TreeViewItem Header="Level 3.2">
+              <TreeViewItem Header="Level 4" />
+            </TreeViewItem>
+          </TreeViewItem>
+          <TreeViewItem Header="Level 2.2"
+                        IsEnabled="False" />
+        </TreeViewItem>
+      </TreeView>
+    </Border>
+  </Design.PreviewWith>
 
-    <Style Selector="TreeViewItem /template/ ContentPresenter#PART_HeaderPresenter">
-        <Setter Property="Padding" Value="2"/>
-    </Style>
+  <Styles.Resources>
+    <x:Double x:Key="TreeViewItemIndent">16</x:Double>
+    <x:Double x:Key="TreeViewItemExpandCollapseChevronSize">12</x:Double>
+    <Thickness x:Key="TreeViewItemExpandCollapseChevronMargin">12, 0, 12, 0</Thickness>
+    <StreamGeometry x:Key="TreeViewItemCollapsedChevronPathData">M 1,0 10,10 l -9,10 -1,-1 L 8,10 -0,1 Z</StreamGeometry>
+    <StreamGeometry x:Key="TreeViewItemExpandedChevronPathData">M0,1 L10,10 20,1 19,0 10,8 1,0 Z</StreamGeometry>
+    <converters:MarginMultiplierConverter Indent="{StaticResource TreeViewItemIndent}"
+                                          Left="True"
+                                          x:Key="TreeViewItemLeftMarginConverter" />
+  </Styles.Resources>
 
-    <Style Selector="TreeViewItem /template/ Border#SelectionBorder:pointerover">
-        <Setter Property="Background" Value="{DynamicResource ThemeControlHighlightMidBrush}"/>
-    </Style>
+  <Style Selector="ToggleButton.ExpandCollapseChevron">
+    <Setter Property="Margin" Value="0" />
+    <Setter Property="Width" Value="{StaticResource TreeViewItemExpandCollapseChevronSize}" />
+    <Setter Property="Height" Value="{StaticResource TreeViewItemExpandCollapseChevronSize}" />
+    <Setter Property="Template">
+      <ControlTemplate>
+        <Border Background="Transparent"
+                Width="{TemplateBinding Width}"
+                Height="{TemplateBinding Height}"
+                HorizontalAlignment="Center"
+                VerticalAlignment="Center">
+          <Path x:Name="ChevronPath"
+                Fill="{DynamicResource TreeViewItemForeground}"
+                Stretch="Uniform"
+                HorizontalAlignment="Center"
+                VerticalAlignment="Center" />
+        </Border>
+      </ControlTemplate>
+    </Setter>
+  </Style>
 
-    <Style Selector="TreeViewItem:selected /template/ Border#SelectionBorder">
-        <Setter Property="Background" Value="{DynamicResource ThemeAccentBrush4}"/>
-    </Style>
+  <Style Selector="TreeViewItem">
+    <Style.Resources />
+    <Setter Property="Padding" Value="0" />
+    <Setter Property="Background" Value="{DynamicResource TreeViewItemBackground}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource TreeViewItemBorderBrush}" />
+    <Setter Property="BorderThickness" Value="{DynamicResource TreeViewItemBorderThemeThickness}" />
+    <Setter Property="Foreground" Value="{DynamicResource TreeViewItemForeground}" />
+    <Setter Property="MinHeight" Value="{DynamicResource TreeViewItemMinHeight}" />
+    <Setter Property="VerticalAlignment" Value="Center" />
+    <Setter Property="Template">
+      <ControlTemplate>
+        <StackPanel>
+          <Border Name="PART_LayoutRoot"
+                  Classes="TreeViewItemLayoutRoot"
+                  Focusable="True"
+                  Background="{TemplateBinding Background}"
+                  BorderBrush="{TemplateBinding BorderBrush}"
+                  BorderThickness="{TemplateBinding BorderThickness}"
+                  MinHeight="{TemplateBinding MinHeight}"
+                  TemplatedControl.IsTemplateFocusTarget="True">
+            <Grid Name="PART_Header"
+                  ColumnDefinitions="Auto, *"
+                  Margin="{TemplateBinding Level, Mode=OneWay, Converter={StaticResource TreeViewItemLeftMarginConverter}}">
+              <Panel Name="PART_ExpandCollapseChevronContainer"
+                     Margin="{StaticResource TreeViewItemExpandCollapseChevronMargin}">
+                <ToggleButton Name="PART_ExpandCollapseChevron"
+                              Classes="ExpandCollapseChevron"
+                              Focusable="False"
+                              IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
+              </Panel>
+              <ContentPresenter Name="PART_HeaderPresenter"
+                                Grid.Column="1"
+                                Focusable="False"
+                                Content="{TemplateBinding Header}"
+                                HorizontalAlignment="{TemplateBinding HorizontalAlignment}"
+                                VerticalAlignment="{TemplateBinding VerticalAlignment}"
+                                Margin="{TemplateBinding Padding}" />
+            </Grid>
+          </Border>
+          <ItemsPresenter Name="PART_ItemsPresenter"
+                          IsVisible="{TemplateBinding IsExpanded}"
+                          Items="{TemplateBinding Items}"
+                          ItemsPanel="{TemplateBinding ItemsPanel}" />
+        </StackPanel>
+      </ControlTemplate>
+    </Setter>
+  </Style>
 
-    <Style Selector="TreeViewItem:selected /template/ Border#SelectionBorder:focus">
-        <Setter Property="Background" Value="{DynamicResource ThemeAccentBrush3}"/>
-    </Style>
+  <!--  PointerOver state  -->
+  <Style Selector="TreeViewItem /template/ Border#PART_LayoutRoot:pointerover">
+    <Setter Property="Background" Value="{DynamicResource TreeViewItemBackgroundPointerOver}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource TreeViewItemBorderBrushPointerOver}" />
+  </Style>
+  <Style Selector="TreeViewItem /template/ Border#PART_LayoutRoot:pointerover > ContentPresenter#PART_HeaderPresenter">
+    <Setter Property="TextBlock.Foreground" Value="{DynamicResource TreeViewItemForegroundPointerOver}" />
+  </Style>
 
-    <Style Selector="TreeViewItem:selected /template/ Border#SelectionBorder:pointerover">
-        <Setter Property="Background" Value="{DynamicResource ThemeAccentBrush3}"/>
-    </Style>
+  <!--  Pressed state  -->
+  <Style Selector="TreeViewItem:pressed /template/ Border#PART_LayoutRoot:pointerover">
+    <Setter Property="Background" Value="{DynamicResource TreeViewItemBackgroundPressed}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource TreeViewItemBorderBrushPressed}" />
+  </Style>
+  <Style Selector="TreeViewItem:pressed /template/ Border#PART_LayoutRoot:pointerover > ContentPresenter#PART_HeaderPresenter">
+    <Setter Property="TextBlock.Foreground" Value="{DynamicResource TreeViewItemForegroundPressed}" />
+  </Style>
 
-    <Style Selector="TreeViewItem:selected /template/ Border#SelectionBorder:pointerover:focus">
-        <Setter Property="Background" Value="{DynamicResource ThemeAccentBrush2}"/>
-    </Style>
+  <!--  Disabled state  -->
+  <Style Selector="TreeViewItem:disabled /template/ Border#PART_LayoutRoot">
+    <Setter Property="Background" Value="{DynamicResource TreeViewItemBackgroundDisabled}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource TreeViewItemBorderBrushDisabled}" />
+  </Style>
+  <Style Selector="TreeViewItem:disabled /template/ Border#PART_LayoutRoot > ContentPresenter#PART_HeaderPresenter">
+    <Setter Property="TextBlock.Foreground" Value="{DynamicResource TreeViewItemForegroundDisabled}" />
+  </Style>
 
-    <Style Selector="TreeViewItem /template/ ToggleButton#expander:checked">
-        <Setter Property="RenderTransform">
-            <RotateTransform Angle="45"/>
-        </Setter>
-    </Style>
+  <!--  Selected state  -->
+  <Style Selector="TreeViewItem:selected /template/ Border#PART_LayoutRoot">
+    <Setter Property="Background" Value="{DynamicResource TreeViewItemBackgroundSelected}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource TreeViewItemBorderBrushSelected}" />
+  </Style>
+  <Style Selector="TreeViewItem:selected /template/ Border#PART_LayoutRoot > ContentPresenter#PART_HeaderPresenter">
+    <Setter Property="TextBlock.Foreground" Value="{DynamicResource TreeViewItemForegroundSelected}" />
+  </Style>
+
+  <!--  Selected PointerOver state  -->
+  <Style Selector="TreeViewItem:selected /template/ Border#PART_LayoutRoot:pointerover">
+    <Setter Property="Background" Value="{DynamicResource TreeViewItemBackgroundSelectedPointerOver}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource TreeViewItemBorderBrushSelectedPointerOver}" />
+  </Style>
+  <Style Selector="TreeViewItem:selected /template/ Border#PART_LayoutRoot:pointerover > ContentPresenter#PART_HeaderPresenter">
+    <Setter Property="TextBlock.Foreground" Value="{DynamicResource TreeViewItemForegroundSelectedPointerOver}" />
+  </Style>
+
+  <!--  Selected Pressed state  -->
+  <Style Selector="TreeViewItem:pressed:selected /template/ Border#PART_LayoutRoot:pointerover">
+    <Setter Property="Background" Value="{DynamicResource TreeViewItemBackgroundSelectedPressed}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource TreeViewItemBorderBrushSelectedPressed}" />
+  </Style>
+  <Style Selector="TreeViewItem:pressed:selected /template/ Border#PART_LayoutRoot:pointerover > ContentPresenter#PART_HeaderPresenter">
+    <Setter Property="TextBlock.Foreground" Value="{DynamicResource TreeViewItemForegroundSelectedPressed}" />
+  </Style>
+
+  <!--  Disabled Selected state  -->
+  <Style Selector="TreeViewItem:disabled:selected /template/ Border#PART_LayoutRoot">
+    <Setter Property="Background" Value="{DynamicResource TreeViewItemBackgroundSelectedDisabled}" />
+    <Setter Property="BorderBrush" Value="{DynamicResource TreeViewItemBorderBrushSelectedDisabled}" />
+  </Style>
+  <Style Selector="TreeViewItem:disabled:selected /template/ Border#PART_LayoutRoot > ContentPresenter#PART_HeaderPresenter">
+    <Setter Property="TextBlock.Foreground" Value="{DynamicResource TreeViewItemForegroundSelectedDisabled}" />
+  </Style>
+
+  <!--  ExpandCollapseChevron Group states  -->
+  <Style Selector="ToggleButton.ExpandCollapseChevron /template/ Path#ChevronPath">
+    <Setter Property="Data" Value="{StaticResource TreeViewItemCollapsedChevronPathData}" />
+  </Style>
+  <Style Selector="ToggleButton.ExpandCollapseChevron:checked /template/ Path#ChevronPath">
+    <Setter Property="Data" Value="{StaticResource TreeViewItemExpandedChevronPathData}" />
+  </Style>
+  <Style Selector="TreeViewItem:empty /template/ ToggleButton#PART_ExpandCollapseChevron">
+    <Setter Property="IsVisible" Value="False" />
+  </Style>
+  <Style Selector="TreeViewItem:empty /template/ Panel#PART_ExpandCollapseChevronContainer">
+    <Setter Property="Width" Value="{StaticResource TreeViewItemExpandCollapseChevronSize}" />
+  </Style>
 
-    <Style Selector="TreeViewItem:empty /template/ ToggleButton#expander">
-        <Setter Property="IsVisible" Value="False"/>
-    </Style>
 </Styles>

tests/Avalonia.Base.UnitTests/Utilities/MathUtilitiesTests.cs

@@ -199,24 +199,5 @@ namespace Avalonia.Base.UnitTests.Utilities
             var actual = MathUtilities.GreaterThanOrClose(1f, 1f);
             Assert.True(actual);
         }
-
-        [Fact]
-        public void Round_Layout_Value_Without_DPI_Aware()
-        {
-            const double value = 42.5;
-            var expectedValue = Math.Round(value);
-            var actualValue = MathUtilities.RoundLayoutValue(value, 1.0);
-            Assert.Equal(expectedValue, actualValue);
-        }
-
-        [Fact]
-        public void Round_Layout_Value_With_DPI_Aware()
-        {
-            const double dpiScale = 1.25;
-            const double value = 42.5;
-            var expectedValue = Math.Round(value * dpiScale) / dpiScale;
-            var actualValue = MathUtilities.RoundLayoutValue(value, dpiScale);
-            Assert.Equal(expectedValue, actualValue);
-        }
     }
 }

tests/Avalonia.Controls.UnitTests/Presenters/ScrollContentPresenterTests.cs

@@ -117,13 +117,17 @@ namespace Avalonia.Controls.UnitTests.Presenters
                     Width = 150,
                     Height = 150,
                 },
-                Offset = new Vector(25, 25),
             };
 
             target.UpdateChild();
             target.Measure(new Size(100, 100));
             target.Arrange(new Rect(0, 0, 100, 100));
 
+            target.Offset = new Vector(25, 25);
+
+            target.Measure(new Size(100, 100));
+            target.Arrange(new Rect(0, 0, 100, 100));
+
             Assert.Equal(new Rect(-25, -25, 150, 150), content.Bounds);
         }
 
@@ -345,4 +349,4 @@ namespace Avalonia.Controls.UnitTests.Presenters
             }
         }
     }
-}
+}

tests/Avalonia.Controls.UnitTests/Presenters/ScrollContentPresenterTests_ILogicalScrollable.cs

@@ -59,13 +59,17 @@ namespace Avalonia.Controls.UnitTests
                 CanHorizontallyScroll = true,
                 CanVerticallyScroll = true,
                 Content = scrollable,
-                Offset = new Vector(25, 25),
             };
 
             target.UpdateChild();
             target.Measure(new Size(100, 100));
             target.Arrange(new Rect(0, 0, 100, 100));
 
+            target.Offset = new Vector(25, 25);
+            
+            target.Measure(new Size(100, 100));
+            target.Arrange(new Rect(0, 0, 100, 100));
+
             Assert.Equal(new Rect(-25, -25, 150, 150), scrollable.Bounds);
         }
 

tests/Avalonia.Layout.UnitTests/LayoutHelperTests.cs

@@ -0,0 +1,27 @@
+using System;
+using Xunit;
+
+namespace Avalonia.Layout.UnitTests
+{
+    public class LayoutHelperTests
+    {
+        [Fact]
+        public void Round_Layout_Value_Without_DPI_Aware()
+        {
+            const double value = 42.5;
+            var expectedValue = Math.Round(value);
+            var actualValue = LayoutHelper.RoundLayoutValue(value, 1.0);
+            Assert.Equal(expectedValue, actualValue);
+        }
+
+        [Fact]
+        public void Round_Layout_Value_With_DPI_Aware()
+        {
+            const double dpiScale = 1.25;
+            const double value = 42.5;
+            var expectedValue = Math.Round(value * dpiScale) / dpiScale;
+            var actualValue = LayoutHelper.RoundLayoutValue(value, dpiScale);
+            Assert.Equal(expectedValue, actualValue);
+        }
+    }
+}