Merge branch 'master' into master

samples/ControlCatalog/Pages/ItemsRepeaterPage.xaml

@@ -53,10 +53,12 @@
         <ComboBoxItem>UniformGrid - Horizontal</ComboBoxItem>
       </ComboBox>
       <Button Command="{Binding AddItem}">Add Item</Button>
+      <Button Command="{Binding RemoveItem}">Remove 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>
+      <Button x:Name="scrollToSelected">Scroll to Selected</Button>
     </StackPanel>
     <Border BorderThickness="1" BorderBrush="{DynamicResource SystemControlHighlightBaseMediumLowBrush}" Margin="0 0 0 16">
       <ScrollViewer Name="scroller"

samples/ControlCatalog/Pages/ItemsRepeaterPage.xaml.cs

@@ -15,8 +15,10 @@ namespace ControlCatalog.Pages
         private readonly ItemsRepeaterPageViewModel _viewModel;
         private ItemsRepeater _repeater;
         private ScrollViewer _scroller;
+        private int _selectedIndex;
         private Button _scrollToLast;
         private Button _scrollToRandom;
+        private Button _scrollToSelected;
         private Random _random = new Random(0);
 
         public ItemsRepeaterPage()
@@ -26,10 +28,12 @@ namespace ControlCatalog.Pages
             _scroller = this.FindControl<ScrollViewer>("scroller");
             _scrollToLast = this.FindControl<Button>("scrollToLast");
             _scrollToRandom = this.FindControl<Button>("scrollToRandom");
+            _scrollToSelected = this.FindControl<Button>("scrollToSelected");
             _repeater.PointerPressed += RepeaterClick;
             _repeater.KeyDown += RepeaterOnKeyDown;
             _scrollToLast.Click += scrollToLast_Click;
             _scrollToRandom.Click += scrollToRandom_Click;
+            _scrollToSelected.Click += scrollToSelected_Click;
             DataContext = _viewModel = new ItemsRepeaterPageViewModel();
         }
 
@@ -121,6 +125,7 @@ namespace ControlCatalog.Pages
         {
             var item = (e.Source as TextBlock)?.DataContext as ItemsRepeaterPageViewModel.Item;
             _viewModel.SelectedItem = item;
+            _selectedIndex = _viewModel.Items.IndexOf(item);
         }
 
         private void RepeaterOnKeyDown(object sender, KeyEventArgs e)
@@ -140,5 +145,10 @@ namespace ControlCatalog.Pages
         {
             ScrollTo(_random.Next(_viewModel.Items.Count - 1));
         }
+
+        private void scrollToSelected_Click(object sender, Avalonia.Interactivity.RoutedEventArgs e)
+        {
+            ScrollTo(_selectedIndex);
+        }
     }
 }

samples/ControlCatalog/ViewModels/ItemsRepeaterPageViewModel.cs

@@ -31,6 +31,19 @@ namespace ControlCatalog.ViewModels
             Items.Insert(index + 1, new Item(index + 1) { Text = $"New Item {_newItemIndex++}" });
         }
 
+        public void RemoveItem()
+        {
+            if (SelectedItem is not null)
+            {
+                Items.Remove(SelectedItem);
+                SelectedItem = null;
+            }
+            else if (Items.Count > 0)
+            {
+                Items.RemoveAt(Items.Count - 1);
+            }
+        }
+
         public void RandomizeHeights()
         {
             var random = new Random();

samples/SampleControls/HamburgerMenu/HamburgerMenu.cs

@@ -43,14 +43,13 @@ namespace ControlSamples
             _splitView = e.NameScope.Find<SplitView>("PART_NavigationPane");
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == BoundsProperty && _splitView is not null)
             {
-                var oldBounds = change.OldValue.GetValueOrDefault<Rect>();
-                var newBounds = change.NewValue.GetValueOrDefault<Rect>();
+                var (oldBounds, newBounds) = change.GetOldAndNewValue<Rect>();
                 EnsureSplitViewMode(oldBounds, newBounds);
             }
         }

src/Avalonia.Base/Animation/Animatable.cs

@@ -87,12 +87,13 @@ namespace Avalonia.Animation
             }
         }
 
-        protected sealed override void OnPropertyChangedCore<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected sealed override void OnPropertyChangedCore(AvaloniaPropertyChangedEventArgs change)
         {
             if (change.Property == TransitionsProperty && change.IsEffectiveValueChange)
             {
-                var oldTransitions = change.OldValue.GetValueOrDefault<Transitions>();
-                var newTransitions = change.NewValue.GetValueOrDefault<Transitions>();
+                var e = (AvaloniaPropertyChangedEventArgs<Transitions?>)change;
+                var oldTransitions = e.OldValue.GetValueOrDefault();
+                var newTransitions = e.NewValue.GetValueOrDefault();
 
                 // When transitions are replaced, we add the new transitions before removing the old
                 // transitions, so that when the old transition being disposed causes the value to

src/Avalonia.Base/AvaloniaObject.cs

@@ -5,6 +5,7 @@ using Avalonia.Data;
 using Avalonia.Diagnostics;
 using Avalonia.Logging;
 using Avalonia.PropertyStore;
+using Avalonia.Reactive;
 using Avalonia.Threading;
 
 namespace Avalonia
@@ -15,13 +16,13 @@ namespace Avalonia
     /// <remarks>
     /// This class is analogous to DependencyObject in WPF.
     /// </remarks>
-    public class AvaloniaObject : IAvaloniaObject, IAvaloniaObjectDebug, INotifyPropertyChanged, IValueSink
+    public class AvaloniaObject : IAvaloniaObject, IAvaloniaObjectDebug, INotifyPropertyChanged
     {
-        private IAvaloniaObject? _inheritanceParent;
+        private AvaloniaObject? _inheritanceParent;
         private List<IDisposable>? _directBindings;
         private PropertyChangedEventHandler? _inpcChanged;
         private EventHandler<AvaloniaPropertyChangedEventArgs>? _propertyChanged;
-        private List<IAvaloniaObject>? _inheritanceChildren;
+        private List<AvaloniaObject>? _inheritanceChildren;
         private ValueStore? _values;
         private bool _batchUpdate;
 
@@ -58,7 +59,7 @@ namespace Avalonia
         /// <value>
         /// The inheritance parent.
         /// </value>
-        protected IAvaloniaObject? InheritanceParent
+        protected AvaloniaObject? InheritanceParent
         {
             get
             {
@@ -320,14 +321,14 @@ namespace Avalonia
         /// <param name="property">The property.</param>
         /// <param name="value">The value.</param>
         /// <param name="priority">The priority of the value.</param>
-        public void SetValue(
+        public IDisposable? SetValue(
             AvaloniaProperty property,
             object? value,
             BindingPriority priority = BindingPriority.LocalValue)
         {
             property = property ?? throw new ArgumentNullException(nameof(property));
 
-            property.RouteSetValue(this, value, priority);
+            return property.RouteSetValue(this, value, priority);
         }
 
         /// <summary>
@@ -385,6 +386,26 @@ namespace Avalonia
             SetDirectValueUnchecked(property, value);
         }
 
+        /// <summary>
+        /// Binds a <see cref="AvaloniaProperty"/> to an observable.
+        /// </summary>
+        /// <param name="property">The property.</param>
+        /// <param name="source">The observable.</param>
+        /// <param name="priority">The priority of the binding.</param>
+        /// <returns>
+        /// A disposable which can be used to terminate the binding.
+        /// </returns>
+        public IDisposable Bind(
+            AvaloniaProperty property,
+            IObservable<object?> source,
+            BindingPriority priority = BindingPriority.LocalValue)
+        {
+            property = property ?? throw new ArgumentNullException(nameof(property));
+            source = source ?? throw new ArgumentNullException(nameof(source));
+
+            return property.RouteBind(this, source.ToBindingValue(), priority);
+        }
+
         /// <summary>
         /// Binds a <see cref="AvaloniaProperty"/> to an observable.
         /// </summary>
@@ -445,9 +466,8 @@ namespace Avalonia
         /// <summary>
         /// Coerces the specified <see cref="AvaloniaProperty"/>.
         /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
         /// <param name="property">The property.</param>
-        public void CoerceValue<T>(StyledPropertyBase<T> property)
+        public void CoerceValue(AvaloniaProperty property)
         {
             _values?.CoerceValue(property);
         }
@@ -475,19 +495,19 @@ namespace Avalonia
         }
 
         /// <inheritdoc/>
-        void IAvaloniaObject.AddInheritanceChild(IAvaloniaObject child)
+        internal void AddInheritanceChild(AvaloniaObject child)
         {
-            _inheritanceChildren ??= new List<IAvaloniaObject>();
+            _inheritanceChildren ??= new List<AvaloniaObject>();
             _inheritanceChildren.Add(child);
         }
         
         /// <inheritdoc/>
-        void IAvaloniaObject.RemoveInheritanceChild(IAvaloniaObject child)
+        internal void RemoveInheritanceChild(AvaloniaObject child)
         {
             _inheritanceChildren?.Remove(child);
         }
 
-        void IAvaloniaObject.InheritedPropertyChanged<T>(
+        internal void InheritedPropertyChanged<T>(
             AvaloniaProperty<T> property,
             Optional<T> oldValue,
             Optional<T> newValue)
@@ -504,7 +524,7 @@ namespace Avalonia
             return _propertyChanged?.GetInvocationList();
         }
 
-        void IValueSink.ValueChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        internal void ValueChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
         {
             var property = (StyledPropertyBase<T>)change.Property;
 
@@ -543,7 +563,7 @@ namespace Avalonia
             }
         }
 
-        void IValueSink.Completed<T>(
+        internal void Completed<T>(
             StyledPropertyBase<T> property,
             IPriorityValueEntry entry,
             Optional<T> oldValue) 
@@ -554,7 +574,7 @@ namespace Avalonia
                 oldValue,
                 default,
                 BindingPriority.Unset);
-            ((IValueSink)this).ValueChanged(change);
+            ValueChanged(change);
         }
 
         /// <summary>
@@ -565,14 +585,11 @@ namespace Avalonia
         /// <param name="oldParent">The old inheritance parent.</param>
         internal void InheritanceParentChanged<T>(
             StyledPropertyBase<T> property,
-            IAvaloniaObject? oldParent)
+            AvaloniaObject? oldParent)
         {
-            var oldValue = oldParent switch
-            {
-                AvaloniaObject o => o.GetValueOrInheritedOrDefault(property),
-                null => property.GetDefaultValue(GetType()),
-                _ => oldParent.GetValue(property)
-            };
+            var oldValue = oldParent is not null ?
+                oldParent.GetValueOrInheritedOrDefault(property) :
+                property.GetDefaultValue(GetType());
 
             var newValue = GetInheritedOrDefault(property);
 
@@ -629,10 +646,12 @@ namespace Avalonia
         /// enabled.
         /// </summary>
         /// <param name="property">The property.</param>
-        /// <param name="value">The new binding value for the property.</param>
-        protected virtual void UpdateDataValidation<T>(
-            AvaloniaProperty<T> property,
-            BindingValue<T> value)
+        /// <param name="state">The current data binding state.</param>
+        /// <param name="error">The current data binding error, if any.</param>
+        protected virtual void UpdateDataValidation(
+            AvaloniaProperty property,
+            BindingValueType state,
+            Exception? error)
         {
         }
 
@@ -640,7 +659,7 @@ namespace Avalonia
         /// Called when a avalonia property changes on the object.
         /// </summary>
         /// <param name="change">The property change details.</param>
-        protected virtual void OnPropertyChangedCore<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected virtual void OnPropertyChangedCore(AvaloniaPropertyChangedEventArgs change)
         {
             if (change.IsEffectiveValueChange)
             {
@@ -652,7 +671,7 @@ namespace Avalonia
         /// Called when a avalonia property changes on the object.
         /// </summary>
         /// <param name="change">The property change details.</param>
-        protected virtual void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected virtual void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
         }
 
@@ -843,7 +862,7 @@ namespace Avalonia
 
             if (metadata.EnableDataValidation == true)
             {
-                UpdateDataValidation(property, value);
+                UpdateDataValidation(property, value.Type, value.Error);
             }
         }
 

src/Avalonia.Base/AvaloniaObjectExtensions.cs

@@ -25,7 +25,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets an observable for a <see cref="AvaloniaProperty"/>.
+        /// Gets an observable for an <see cref="AvaloniaProperty"/>.
         /// </summary>
         /// <param name="o">The object.</param>
         /// <param name="property">The property.</param>
@@ -44,7 +44,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets an observable for a <see cref="AvaloniaProperty"/>.
+        /// Gets an observable for an <see cref="AvaloniaProperty"/>.
         /// </summary>
         /// <param name="o">The object.</param>
         /// <typeparam name="T">The property type.</typeparam>
@@ -64,7 +64,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets an observable for a <see cref="AvaloniaProperty"/>.
+        /// Gets an observable for an <see cref="AvaloniaProperty"/>.
         /// </summary>
         /// <param name="o">The object.</param>
         /// <param name="property">The property.</param>
@@ -85,7 +85,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets an observable for a <see cref="AvaloniaProperty"/>.
+        /// Gets an observable for an <see cref="AvaloniaProperty"/>.
         /// </summary>
         /// <param name="o">The object.</param>
         /// <typeparam name="T">The property type.</typeparam>
@@ -128,7 +128,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets a subject for a <see cref="AvaloniaProperty"/>.
+        /// Gets a subject for an <see cref="AvaloniaProperty"/>.
         /// </summary>
         /// <param name="o">The object.</param>
         /// <param name="property">The property.</param>
@@ -150,7 +150,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets a subject for a <see cref="AvaloniaProperty"/>.
+        /// Gets a subject for an <see cref="AvaloniaProperty"/>.
         /// </summary>
         /// <typeparam name="T">The property type.</typeparam>
         /// <param name="o">The object.</param>
@@ -230,30 +230,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Binds a <see cref="AvaloniaProperty"/> to an observable.
-        /// </summary>
-        /// <param name="target">The object.</param>
-        /// <param name="property">The property.</param>
-        /// <param name="source">The observable.</param>
-        /// <param name="priority">The priority of the binding.</param>
-        /// <returns>
-        /// A disposable which can be used to terminate the binding.
-        /// </returns>
-        public static IDisposable Bind(
-            this IAvaloniaObject target,
-            AvaloniaProperty property,
-            IObservable<BindingValue<object?>> source,
-            BindingPriority priority = BindingPriority.LocalValue)
-        {
-            target = target ?? throw new ArgumentNullException(nameof(target));
-            property = property ?? throw new ArgumentNullException(nameof(property));
-            source = source ?? throw new ArgumentNullException(nameof(source));
-
-            return property.RouteBind(target, source, priority);
-        }
-
-        /// <summary>
-        /// Binds a <see cref="AvaloniaProperty"/> to an observable.
+        /// Binds an <see cref="AvaloniaProperty"/> to an observable.
         /// </summary>
         /// <typeparam name="T">The type of the property.</typeparam>
         /// <param name="target">The object.</param>
@@ -273,42 +250,22 @@ namespace Avalonia
             property = property ?? throw new ArgumentNullException(nameof(property));
             source = source ?? throw new ArgumentNullException(nameof(source));
 
-            return property switch
+            if (target is AvaloniaObject ao)
             {
-                StyledPropertyBase<T> styled => target.Bind(styled, source, priority),
-                DirectPropertyBase<T> direct => target.Bind(direct, source),
-                _ => throw new NotSupportedException("Unsupported AvaloniaProperty type."),
-            };
-        }
+                return property switch
+                {
+                    StyledPropertyBase<T> styled => ao.Bind(styled, source, priority),
+                    DirectPropertyBase<T> direct => ao.Bind(direct, source),
+                    _ => throw new NotSupportedException("Unsupported AvaloniaProperty type."),
+                };
+            }
 
-        /// <summary>
-        /// Binds a <see cref="AvaloniaProperty"/> to an observable.
-        /// </summary>
-        /// <param name="target">The object.</param>
-        /// <param name="property">The property.</param>
-        /// <param name="source">The observable.</param>
-        /// <param name="priority">The priority of the binding.</param>
-        /// <returns>
-        /// A disposable which can be used to terminate the binding.
-        /// </returns>
-        public static IDisposable Bind(
-            this IAvaloniaObject target,
-            AvaloniaProperty property,
-            IObservable<object?> source,
-            BindingPriority priority = BindingPriority.LocalValue)
-        {
-            target = target ?? throw new ArgumentNullException(nameof(target));
-            property = property ?? throw new ArgumentNullException(nameof(property));
-            source = source ?? throw new ArgumentNullException(nameof(source));
+            throw new NotSupportedException("Custom implementations of IAvaloniaObject not supported.");
 
-            return target.Bind(
-                property,
-                source.ToBindingValue(),
-                priority);
         }
 
         /// <summary>
-        /// Binds a <see cref="AvaloniaProperty"/> to an observable.
+        /// Binds an <see cref="AvaloniaProperty"/> to an observable.
         /// </summary>
         /// <param name="target">The object.</param>
         /// <param name="property">The property.</param>
@@ -334,7 +291,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Binds a property on an <see cref="IAvaloniaObject"/> to an <see cref="IBinding"/>.
+        /// Binds a property on an <see cref="AvaloniaObject"/> to an <see cref="IBinding"/>.
         /// </summary>
         /// <param name="target">The object.</param>
         /// <param name="property">The property to bind.</param>
@@ -374,56 +331,6 @@ namespace Avalonia
             }
         }
 
-        /// <summary>
-        /// Clears a <see cref="AvaloniaProperty"/>'s local value.
-        /// </summary>
-        /// <param name="target">The object.</param>
-        /// <param name="property">The property.</param>
-        public static void ClearValue(this IAvaloniaObject target, AvaloniaProperty property)
-        {
-            target = target ?? throw new ArgumentNullException(nameof(target));
-            property = property ?? throw new ArgumentNullException(nameof(property));
-
-            property.RouteClearValue(target);
-        }
-
-        /// <summary>
-        /// Clears a <see cref="AvaloniaProperty"/>'s local value.
-        /// </summary>
-        /// <param name="target">The object.</param>
-        /// <param name="property">The property.</param>
-        public static void ClearValue<T>(this IAvaloniaObject target, AvaloniaProperty<T> property)
-        {
-            target = target ?? throw new ArgumentNullException(nameof(target));
-            property = property ?? throw new ArgumentNullException(nameof(property));
-
-            switch (property)
-            {
-                case StyledPropertyBase<T> styled:
-                    target.ClearValue(styled);
-                    break;
-                case DirectPropertyBase<T> direct:
-                    target.ClearValue(direct);
-                    break;
-                default:
-                    throw new NotSupportedException("Unsupported AvaloniaProperty type.");
-            }
-        }
-
-        /// <summary>
-        /// Gets a <see cref="AvaloniaProperty"/> value.
-        /// </summary>
-        /// <param name="target">The object.</param>
-        /// <param name="property">The property.</param>
-        /// <returns>The value.</returns>
-        public static object? GetValue(this IAvaloniaObject target, AvaloniaProperty property)
-        {
-            target = target ?? throw new ArgumentNullException(nameof(target));
-            property = property ?? throw new ArgumentNullException(nameof(property));
-
-            return property.RouteGetValue(target);
-        }
-
         /// <summary>
         /// Gets a <see cref="AvaloniaProperty"/> value.
         /// </summary>
@@ -436,12 +343,18 @@ namespace Avalonia
             target = target ?? throw new ArgumentNullException(nameof(target));
             property = property ?? throw new ArgumentNullException(nameof(property));
 
-            return property switch
+            if (target is AvaloniaObject ao)
             {
-                StyledPropertyBase<T> styled => target.GetValue(styled),
-                DirectPropertyBase<T> direct => target.GetValue(direct),
-                _ => throw new NotSupportedException("Unsupported AvaloniaProperty type.")
-            };
+                return property switch
+                {
+                    StyledPropertyBase<T> styled => ao.GetValue(styled),
+                    DirectPropertyBase<T> direct => ao.GetValue(direct),
+                    _ => throw new NotSupportedException("Unsupported AvaloniaProperty type.")
+                };
+
+            }
+
+            throw new NotSupportedException("Custom implementations of IAvaloniaObject not supported.");
         }
 
         /// <summary>
@@ -456,7 +369,7 @@ namespace Avalonia
         /// <see cref="AvaloniaProperty.UnsetValue"/>. Note that this method does not return
         /// property values that come from inherited or default values.
         /// 
-        /// For direct properties returns <see cref="GetValue(IAvaloniaObject, AvaloniaProperty)"/>.
+        /// For direct properties returns the current value of the property.
         /// </remarks>
         public static object? GetBaseValue(
             this IAvaloniaObject target,
@@ -466,7 +379,9 @@ namespace Avalonia
             target = target ?? throw new ArgumentNullException(nameof(target));
             property = property ?? throw new ArgumentNullException(nameof(property));
 
-            return property.RouteGetBaseValue(target, maxPriority);
+            if (target is AvaloniaObject ao)
+                return property.RouteGetBaseValue(ao, maxPriority);
+            throw new NotSupportedException("Custom implementations of IAvaloniaObject not supported.");
         }
 
         /// <summary>
@@ -481,8 +396,7 @@ namespace Avalonia
         /// <see cref="Optional{T}.Empty"/>. Note that this method does not return property values
         /// that come from inherited or default values.
         /// 
-        /// For direct properties returns
-        /// <see cref="IAvaloniaObject.GetValue{T}(DirectPropertyBase{T})"/>.
+        /// For direct properties returns the current value of the property.
         /// </remarks>
         public static Optional<T> GetBaseValue<T>(
             this IAvaloniaObject target,
@@ -492,69 +406,18 @@ namespace Avalonia
             target = target ?? throw new ArgumentNullException(nameof(target));
             property = property ?? throw new ArgumentNullException(nameof(property));
 
-            target = target ?? throw new ArgumentNullException(nameof(target));
-            property = property ?? throw new ArgumentNullException(nameof(property));
-
-            return property switch
+            if (target is AvaloniaObject ao)
             {
-                StyledPropertyBase<T> styled => target.GetBaseValue(styled, maxPriority),
-                DirectPropertyBase<T> direct => target.GetValue(direct),
-                _ => throw new NotSupportedException("Unsupported AvaloniaProperty type.")
-            };
-        }
-
-        /// <summary>
-        /// Sets a <see cref="AvaloniaProperty"/> value.
-        /// </summary>
-        /// <param name="target">The object.</param>
-        /// <param name="property">The property.</param>
-        /// <param name="value">The value.</param>
-        /// <param name="priority">The priority of the value.</param>
-        /// <returns>
-        /// An <see cref="IDisposable"/> if setting the property can be undone, otherwise null.
-        /// </returns>
-        public static IDisposable? SetValue(
-            this IAvaloniaObject target,
-            AvaloniaProperty property,
-            object? value,
-            BindingPriority priority = BindingPriority.LocalValue)
-        {
-            target = target ?? throw new ArgumentNullException(nameof(target));
-            property = property ?? throw new ArgumentNullException(nameof(property));
-
-            return property.RouteSetValue(target, value, priority);
-        }
-
-        /// <summary>
-        /// Sets a <see cref="AvaloniaProperty"/> value.
-        /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
-        /// <param name="target">The object.</param>
-        /// <param name="property">The property.</param>
-        /// <param name="value">The value.</param>
-        /// <param name="priority">The priority of the value.</param>
-        /// <returns>
-        /// An <see cref="IDisposable"/> if setting the property can be undone, otherwise null.
-        /// </returns>
-        public static IDisposable? SetValue<T>(
-            this IAvaloniaObject target,
-            AvaloniaProperty<T> property,
-            T value,
-            BindingPriority priority = BindingPriority.LocalValue)
-        {
-            target = target ?? throw new ArgumentNullException(nameof(target));
-            property = property ?? throw new ArgumentNullException(nameof(property));
+                return property switch
+                {
+                    StyledPropertyBase<T> styled => ao.GetBaseValue(styled, maxPriority),
+                    DirectPropertyBase<T> direct => ao.GetValue(direct),
+                    _ => throw new NotSupportedException("Unsupported AvaloniaProperty type.")
+                };
 
-            switch (property)
-            {
-                case StyledPropertyBase<T> styled:
-                    return target.SetValue(styled, value, priority);
-                case DirectPropertyBase<T> direct:
-                    target.SetValue(direct, value);
-                    return null;
-                default:
-                    throw new NotSupportedException("Unsupported AvaloniaProperty type.");
             }
+
+            throw new NotSupportedException("Custom implementations of IAvaloniaObject not supported.");
         }
 
         /// <summary>
@@ -622,17 +485,6 @@ namespace Avalonia
             return observable.Subscribe(e => SubscribeAdapter(e, handler));
         }
 
-        /// <summary>
-        /// Gets a description of a property that van be used in observables.
-        /// </summary>
-        /// <param name="o">The object.</param>
-        /// <param name="property">The property</param>
-        /// <returns>The description.</returns>
-        private static string GetDescription(IAvaloniaObject o, AvaloniaProperty property)
-        {
-            return $"{o.GetType().Name}.{property.Name}";
-        }
-
         /// <summary>
         /// Observer method for <see cref="AddClassHandler{TTarget}(IObservable{AvaloniaPropertyChangedEventArgs},
         /// Func{TTarget, Action{AvaloniaPropertyChangedEventArgs}})"/>.

src/Avalonia.Base/AvaloniaProperty.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using Avalonia.Data;
 using Avalonia.Data.Core;
+using Avalonia.Styling;
 using Avalonia.Utilities;
 
 namespace Avalonia
@@ -454,33 +455,24 @@ namespace Avalonia
             return Name;
         }
 
-        /// <summary>
-        /// Uses the visitor pattern to resolve an untyped property to a typed property.
-        /// </summary>
-        /// <typeparam name="TData">The type of user data passed.</typeparam>
-        /// <param name="visitor">The visitor which will accept the typed property.</param>
-        /// <param name="data">The user data to pass.</param>
-        public abstract void Accept<TData>(IAvaloniaPropertyVisitor<TData> visitor, ref TData data)
-            where TData : struct;
-
         /// <summary>
         /// Routes an untyped ClearValue call to a typed call.
         /// </summary>
         /// <param name="o">The object instance.</param>
-        internal abstract void RouteClearValue(IAvaloniaObject o);
+        internal abstract void RouteClearValue(AvaloniaObject o);
 
         /// <summary>
         /// Routes an untyped GetValue call to a typed call.
         /// </summary>
         /// <param name="o">The object instance.</param>
-        internal abstract object? RouteGetValue(IAvaloniaObject o);
+        internal abstract object? RouteGetValue(AvaloniaObject o);
 
         /// <summary>
         /// Routes an untyped GetBaseValue call to a typed call.
         /// </summary>
         /// <param name="o">The object instance.</param>
         /// <param name="maxPriority">The maximum priority for the value.</param>
-        internal abstract object? RouteGetBaseValue(IAvaloniaObject o, BindingPriority maxPriority);
+        internal abstract object? RouteGetBaseValue(AvaloniaObject o, BindingPriority maxPriority);
 
         /// <summary>
         /// Routes an untyped SetValue call to a typed call.
@@ -492,7 +484,7 @@ namespace Avalonia
         /// An <see cref="IDisposable"/> if setting the property can be undone, otherwise null.
         /// </returns>
         internal abstract IDisposable? RouteSetValue(
-            IAvaloniaObject o,
+            AvaloniaObject o,
             object? value,
             BindingPriority priority);
 
@@ -503,11 +495,12 @@ namespace Avalonia
         /// <param name="source">The binding source.</param>
         /// <param name="priority">The priority.</param>
         internal abstract IDisposable RouteBind(
-            IAvaloniaObject o,
+            AvaloniaObject o,
             IObservable<BindingValue<object?>> source,
             BindingPriority priority);
 
-        internal abstract void RouteInheritanceParentChanged(AvaloniaObject o, IAvaloniaObject? oldParent);
+        internal abstract void RouteInheritanceParentChanged(AvaloniaObject o, AvaloniaObject? oldParent);
+        internal abstract ISetterInstance CreateSetterInstance(IStyleable target, object? value);
 
         /// <summary>
         /// Overrides the metadata for the property on the specified type.

src/Avalonia.Base/AvaloniaPropertyChangedExtensions.cs

@@ -0,0 +1,43 @@
+namespace Avalonia
+{
+    /// <summary>
+    /// Provides extensions for <see cref="AvaloniaPropertyChangedEventArgs"/>.
+    /// </summary>
+    public static class AvaloniaPropertyChangedExtensions
+    {
+        /// <summary>
+        /// Gets a typed value from <see cref="AvaloniaPropertyChangedEventArgs.OldValue"/>.
+        /// </summary>
+        /// <typeparam name="T">The value type.</typeparam>
+        /// <param name="e">The event args.</param>
+        /// <returns>The value.</returns>
+        public static T GetOldValue<T>(this AvaloniaPropertyChangedEventArgs e)
+        {
+            return ((AvaloniaPropertyChangedEventArgs<T>)e).OldValue.GetValueOrDefault()!;
+        }
+
+        /// <summary>
+        /// Gets a typed value from <see cref="AvaloniaPropertyChangedEventArgs.NewValue"/>.
+        /// </summary>
+        /// <typeparam name="T">The value type.</typeparam>
+        /// <param name="e">The event args.</param>
+        /// <returns>The value.</returns>
+        public static T GetNewValue<T>(this AvaloniaPropertyChangedEventArgs e)
+        {
+            return ((AvaloniaPropertyChangedEventArgs<T>)e).NewValue.GetValueOrDefault()!;
+        }
+
+        /// <summary>
+        /// Gets a typed value from <see cref="AvaloniaPropertyChangedEventArgs.OldValue"/> and
+        /// <see cref="AvaloniaPropertyChangedEventArgs.NewValue"/>.
+        /// </summary>
+        /// <typeparam name="T">The value type.</typeparam>
+        /// <param name="e">The event args.</param>
+        /// <returns>The value.</returns>
+        public static (T oldValue, T newValue) GetOldAndNewValue<T>(this AvaloniaPropertyChangedEventArgs e)
+        {
+            var ev = (AvaloniaPropertyChangedEventArgs<T>)e;
+            return (ev.OldValue.GetValueOrDefault()!, ev.NewValue.GetValueOrDefault()!);
+        }
+    }
+}

src/Avalonia.Base/DirectPropertyBase.cs

@@ -1,6 +1,7 @@
 using System;
 using Avalonia.Data;
 using Avalonia.Reactive;
+using Avalonia.Styling;
 using Avalonia.Utilities;
 
 namespace Avalonia
@@ -121,31 +122,25 @@ namespace Avalonia
         }
 
         /// <inheritdoc/>
-        public override void Accept<TData>(IAvaloniaPropertyVisitor<TData> visitor, ref TData data)
-        {
-            visitor.Visit(this, ref data);
-        }
-
-        /// <inheritdoc/>
-        internal override void RouteClearValue(IAvaloniaObject o)
+        internal override void RouteClearValue(AvaloniaObject o)
         {
             o.ClearValue<TValue>(this);
         }
 
         /// <inheritdoc/>
-        internal override object? RouteGetValue(IAvaloniaObject o)
+        internal override object? RouteGetValue(AvaloniaObject o)
         {
             return o.GetValue<TValue>(this);
         }
 
-        internal override object? RouteGetBaseValue(IAvaloniaObject o, BindingPriority maxPriority)
+        internal override object? RouteGetBaseValue(AvaloniaObject o, BindingPriority maxPriority)
         {
             return o.GetValue<TValue>(this);
         }
 
         /// <inheritdoc/>
         internal override IDisposable? RouteSetValue(
-            IAvaloniaObject o,
+            AvaloniaObject o,
             object? value,
             BindingPriority priority)
         {
@@ -169,7 +164,7 @@ namespace Avalonia
 
         /// <inheritdoc/>
         internal override IDisposable RouteBind(
-            IAvaloniaObject o,
+            AvaloniaObject o,
             IObservable<BindingValue<object?>> source,
             BindingPriority priority)
         {
@@ -177,9 +172,34 @@ namespace Avalonia
             return o.Bind<TValue>(this, adapter);
         }
 
-        internal override void RouteInheritanceParentChanged(AvaloniaObject o, IAvaloniaObject? oldParent)
+        internal override void RouteInheritanceParentChanged(AvaloniaObject o, AvaloniaObject? oldParent)
         {
             throw new NotSupportedException("Direct properties do not support inheritance.");
         }
+
+        internal override ISetterInstance CreateSetterInstance(IStyleable target, object? value)
+        {
+            if (value is IBinding binding)
+            {
+                return new PropertySetterBindingInstance<TValue>(
+                    target,
+                    this,
+                    binding);
+            }
+            else if (value is ITemplate template && !typeof(ITemplate).IsAssignableFrom(PropertyType))
+            {
+                return new PropertySetterLazyInstance<TValue>(
+                    target,
+                    this,
+                    () => (TValue)template.Build());
+            }
+            else
+            {
+                return new PropertySetterInstance<TValue>(
+                    target,
+                    this,
+                    (TValue)value!);
+            }
+        }
     }
 }

src/Avalonia.Base/GeometryGroup.cs

@@ -68,7 +68,7 @@ namespace Avalonia.Media
             return null;
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 

src/Avalonia.Base/IAvaloniaObject.cs

@@ -17,42 +17,14 @@ namespace Avalonia
         /// Clears an <see cref="AvaloniaProperty"/>'s local value.
         /// </summary>
         /// <param name="property">The property.</param>
-        void ClearValue<T>(StyledPropertyBase<T> property);
-
-        /// <summary>
-        /// Clears an <see cref="AvaloniaProperty"/>'s local value.
-        /// </summary>
-        /// <param name="property">The property.</param>
-        void ClearValue<T>(DirectPropertyBase<T> property);
-
-        /// <summary>
-        /// Gets a <see cref="AvaloniaProperty"/> value.
-        /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
-        /// <param name="property">The property.</param>
-        /// <returns>The value.</returns>
-        T GetValue<T>(StyledPropertyBase<T> property);
+        void ClearValue(AvaloniaProperty property);
 
         /// <summary>
         /// Gets a <see cref="AvaloniaProperty"/> value.
         /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
         /// <param name="property">The property.</param>
         /// <returns>The value.</returns>
-        T GetValue<T>(DirectPropertyBase<T> property);
-
-        /// <summary>
-        /// Gets an <see cref="AvaloniaProperty"/> base value.
-        /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
-        /// <param name="property">The property.</param>
-        /// <param name="maxPriority">The maximum priority for the value.</param>
-        /// <remarks>
-        /// Gets the value of the property, if set on this object with a priority equal or lower to
-        /// <paramref name="maxPriority"/>, otherwise <see cref="Optional{T}.Empty"/>. Note that
-        /// this method does not return property values that come from inherited or default values.
-        /// </remarks>
-        Optional<T> GetBaseValue<T>(StyledPropertyBase<T> property, BindingPriority maxPriority);
+        object? GetValue(AvaloniaProperty property);
 
         /// <summary>
         /// Checks whether a <see cref="AvaloniaProperty"/> is animating.
@@ -71,93 +43,35 @@ namespace Avalonia
         /// <summary>
         /// Sets a <see cref="AvaloniaProperty"/> value.
         /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
         /// <param name="property">The property.</param>
         /// <param name="value">The value.</param>
         /// <param name="priority">The priority of the value.</param>
         /// <returns>
         /// An <see cref="IDisposable"/> if setting the property can be undone, otherwise null.
         /// </returns>
-        IDisposable? SetValue<T>(
-            StyledPropertyBase<T> property,
-            T value,
+        IDisposable? SetValue(
+            AvaloniaProperty property,
+            object? value,
             BindingPriority priority = BindingPriority.LocalValue);
 
-        /// <summary>
-        /// Sets a <see cref="AvaloniaProperty"/> value.
-        /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
-        /// <param name="property">The property.</param>
-        /// <param name="value">The value.</param>
-        void SetValue<T>(DirectPropertyBase<T> property, T value);
-
         /// <summary>
         /// Binds a <see cref="AvaloniaProperty"/> to an observable.
         /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
         /// <param name="property">The property.</param>
         /// <param name="source">The observable.</param>
         /// <param name="priority">The priority of the binding.</param>
         /// <returns>
         /// A disposable which can be used to terminate the binding.
         /// </returns>
-        IDisposable Bind<T>(
-            StyledPropertyBase<T> property,
-            IObservable<BindingValue<T>> source,
+        IDisposable Bind(
+            AvaloniaProperty property,
+            IObservable<object?> source,
             BindingPriority priority = BindingPriority.LocalValue);
 
-        /// <summary>
-        /// Binds a <see cref="AvaloniaProperty"/> to an observable.
-        /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
-        /// <param name="property">The property.</param>
-        /// <param name="source">The observable.</param>
-        /// <returns>
-        /// A disposable which can be used to terminate the binding.
-        /// </returns>
-        IDisposable Bind<T>(
-            DirectPropertyBase<T> property,
-            IObservable<BindingValue<T>> source);
-
         /// <summary>
         /// Coerces the specified <see cref="AvaloniaProperty"/>.
         /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
         /// <param name="property">The property.</param>
-        void CoerceValue<T>(StyledPropertyBase<T> property);
-
-        /// <summary>
-        /// Registers an object as an inheritance child.
-        /// </summary>
-        /// <param name="child">The inheritance child.</param>
-        /// <remarks>
-        /// Inheritance children will receive a call to
-        /// <see cref="InheritedPropertyChanged{T}(AvaloniaProperty{T}, Optional{T}, Optional{T})"/>
-        /// when an inheritable property value changes on the parent.
-        /// </remarks>
-        void AddInheritanceChild(IAvaloniaObject child);
-
-        /// <summary>
-        /// Unregisters an object as an inheritance child.
-        /// </summary>
-        /// <param name="child">The inheritance child.</param>
-        /// <remarks>
-        /// Removes an inheritance child that was added by a call to
-        /// <see cref="AddInheritanceChild(IAvaloniaObject)"/>.
-        /// </remarks>
-        void RemoveInheritanceChild(IAvaloniaObject child);
-
-        /// <summary>
-        /// Called when an inheritable property changes on an object registered as an inheritance
-        /// parent.
-        /// </summary>
-        /// <typeparam name="T">The type of the value.</typeparam>
-        /// <param name="property">The property that has changed.</param>
-        /// <param name="oldValue"></param>
-        /// <param name="newValue"></param>
-        void InheritedPropertyChanged<T>(
-            AvaloniaProperty<T> property,
-            Optional<T> oldValue,
-            Optional<T> newValue);
+        void CoerceValue(AvaloniaProperty property);
     }
 }

src/Avalonia.Base/Input/InputElement.cs

@@ -601,21 +601,21 @@ namespace Avalonia.Input
         {
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == IsFocusedProperty)
             {
-                UpdatePseudoClasses(change.NewValue.GetValueOrDefault<bool>(), null);
+                UpdatePseudoClasses(change.GetNewValue<bool>(), null);
             }
             else if (change.Property == IsPointerOverProperty)
             {
-                UpdatePseudoClasses(null, change.NewValue.GetValueOrDefault<bool>());
+                UpdatePseudoClasses(null, change.GetNewValue<bool>());
             }
             else if (change.Property == IsKeyboardFocusWithinProperty)
             {
-                PseudoClasses.Set(":focus-within", change.NewValue.GetValueOrDefault<bool>());
+                PseudoClasses.Set(":focus-within", change.GetNewValue<bool>());
             }
         }
 

src/Avalonia.Base/Input/KeyboardNavigation.cs

@@ -58,7 +58,7 @@ namespace Avalonia.Input
         /// <returns>The <see cref="KeyboardNavigationMode"/> for the container.</returns>
         public static int GetTabIndex(IInputElement element)
         {
-            return ((IAvaloniaObject)element).GetValue(TabIndexProperty);
+            return ((AvaloniaObject)element).GetValue(TabIndexProperty);
         }
 
         /// <summary>

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

@@ -610,7 +610,7 @@ namespace Avalonia.Input.Navigation
 
         private static IInputElement? GetActiveElement(IInputElement e)
         {
-            return ((IAvaloniaObject)e).GetValue(KeyboardNavigation.TabOnceActiveElementProperty);
+            return ((AvaloniaObject)e).GetValue(KeyboardNavigation.TabOnceActiveElementProperty);
         }
 
         private static IInputElement GetGroupParent(IInputElement e) => GetGroupParent(e, false);
@@ -655,8 +655,9 @@ namespace Avalonia.Input.Navigation
 
         private static KeyboardNavigationMode GetKeyNavigationMode(IInputElement e)
         {
-            return ((IAvaloniaObject)e).GetValue(KeyboardNavigation.TabNavigationProperty);
+            return ((AvaloniaObject)e).GetValue(KeyboardNavigation.TabNavigationProperty);
         }
+
         private static bool IsFocusScope(IInputElement e) => FocusManager.GetIsFocusScope(e) || GetParent(e) == null;
         private static bool IsGroup(IInputElement e) => GetKeyNavigationMode(e) != KeyboardNavigationMode.Continue;
 

src/Avalonia.Base/Interactivity/IInteractive.cs

@@ -28,21 +28,6 @@ namespace Avalonia.Interactivity
             RoutingStrategies routes = RoutingStrategies.Direct | RoutingStrategies.Bubble,
             bool handledEventsToo = false);
 
-        /// <summary>
-        /// Adds a handler for the specified routed event.
-        /// </summary>
-        /// <typeparam name="TEventArgs">The type of the event's args.</typeparam>
-        /// <param name="routedEvent">The routed event.</param>
-        /// <param name="handler">The handler.</param>
-        /// <param name="routes">The routing strategies to listen to.</param>
-        /// <param name="handledEventsToo">Whether handled events should also be listened for.</param>
-        /// <returns>A disposable that terminates the event subscription.</returns>
-        void AddHandler<TEventArgs>(
-            RoutedEvent<TEventArgs> routedEvent,
-            EventHandler<TEventArgs> handler,
-            RoutingStrategies routes = RoutingStrategies.Direct | RoutingStrategies.Bubble,
-            bool handledEventsToo = false) where TEventArgs : RoutedEventArgs;
-
         /// <summary>
         /// Removes a handler for the specified routed event.
         /// </summary>
@@ -50,15 +35,6 @@ namespace Avalonia.Interactivity
         /// <param name="handler">The handler.</param>
         void RemoveHandler(RoutedEvent routedEvent, Delegate handler);
 
-        /// <summary>
-        /// Removes a handler for the specified routed event.
-        /// </summary>
-        /// <typeparam name="TEventArgs">The type of the event's args.</typeparam>
-        /// <param name="routedEvent">The routed event.</param>
-        /// <param name="handler">The handler.</param>
-        void RemoveHandler<TEventArgs>(RoutedEvent<TEventArgs> routedEvent, EventHandler<TEventArgs> handler)
-            where TEventArgs : RoutedEventArgs;
-
         /// <summary>
         /// Adds the object's handlers for a routed event to an event route.
         /// </summary>

src/Avalonia.Base/Layout/StackLayout.cs

@@ -320,11 +320,11 @@ namespace Avalonia.Layout
             InvalidateLayout();
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             if (change.Property == OrientationProperty)
             {
-                var orientation = change.NewValue.GetValueOrDefault<Orientation>();
+                var orientation = change.GetNewValue<Orientation>();
 
                 //Note: For StackLayout Vertical Orientation means we have a Vertical ScrollOrientation.
                 //Horizontal Orientation means we have a Horizontal ScrollOrientation.

src/Avalonia.Base/Layout/UniformGridLayout.cs

@@ -471,11 +471,11 @@ namespace Avalonia.Layout
             gridState.ClearElementOnDataSourceChange(context, args);
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             if (change.Property == OrientationProperty)
             {
-                var orientation = change.NewValue.GetValueOrDefault<Orientation>();
+                var orientation = change.GetNewValue<Orientation>();
 
                 //Note: For UniformGridLayout Vertical Orientation means we have a Horizontal ScrollOrientation. Horizontal Orientation means we have a Vertical ScrollOrientation.
                 //i.e. the properties are the inverse of each other.
@@ -484,31 +484,31 @@ namespace Avalonia.Layout
             }
             else if (change.Property == MinColumnSpacingProperty)
             {
-                _minColumnSpacing = change.NewValue.GetValueOrDefault<double>();
+                _minColumnSpacing = change.GetNewValue<double>();
             }
             else if (change.Property == MinRowSpacingProperty)
             {
-                _minRowSpacing = change.NewValue.GetValueOrDefault<double>();
+                _minRowSpacing = change.GetNewValue<double>();
             }
             else if (change.Property == ItemsJustificationProperty)
             {
-                _itemsJustification = change.NewValue.GetValueOrDefault<UniformGridLayoutItemsJustification>();
+                _itemsJustification = change.GetNewValue<UniformGridLayoutItemsJustification>();
             }
             else if (change.Property == ItemsStretchProperty)
             {
-                _itemsStretch = change.NewValue.GetValueOrDefault<UniformGridLayoutItemsStretch>();
+                _itemsStretch = change.GetNewValue<UniformGridLayoutItemsStretch>();
             }
             else if (change.Property == MinItemWidthProperty)
             {
-                _minItemWidth = change.NewValue.GetValueOrDefault<double>();
+                _minItemWidth = change.GetNewValue<double>();
             }
             else if (change.Property == MinItemHeightProperty)
             {
-                _minItemHeight = change.NewValue.GetValueOrDefault<double>();
+                _minItemHeight = change.GetNewValue<double>();
             }
             else if (change.Property == MaximumRowsOrColumnsProperty)
             {
-                _maximumRowsOrColumns = change.NewValue.GetValueOrDefault<int>();
+                _maximumRowsOrColumns = change.GetNewValue<int>();
             }
 
             InvalidateLayout();

src/Avalonia.Base/Layout/WrapLayout/WrapLayout.cs

@@ -322,7 +322,7 @@ namespace Avalonia.Layout
             return finalSize;
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 

src/Avalonia.Base/Media/DashStyle.cs

@@ -112,14 +112,13 @@ namespace Avalonia.Media
         /// <returns></returns>
         public ImmutableDashStyle ToImmutable() => new ImmutableDashStyle(Dashes, Offset);
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == DashesProperty)
             {
-                var oldValue = change.OldValue.GetValueOrDefault<AvaloniaList<double>>();
-                var newValue = change.NewValue.GetValueOrDefault<AvaloniaList<double>>();
+                var (oldValue, newValue) = change.GetOldAndNewValue<AvaloniaList<double>>();
 
                 if (oldValue is object)
                 {

src/Avalonia.Base/Media/DrawingImage.cs

@@ -69,7 +69,7 @@ namespace Avalonia.Media
         }
 
         /// <inheritdoc/>
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 

src/Avalonia.Base/Media/Pen.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Media
     /// <summary>
     /// Describes how a stroke is drawn.
     /// </summary>
-    public sealed class Pen : AvaloniaObject, IPen, IWeakEventSubscriber<EventArgs>
+    public sealed class Pen : AvaloniaObject, IPen
     {
         /// <summary>
         /// Defines the <see cref="Brush"/> property.
@@ -48,7 +48,8 @@ namespace Avalonia.Media
         private EventHandler? _invalidated;
         private IAffectsRender? _subscribedToBrush;
         private IAffectsRender? _subscribedToDashes;
-        
+        private TargetWeakEventSubscriber<Pen, EventArgs>? _weakSubscriber;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="Pen"/> class.
         /// </summary>
@@ -192,7 +193,7 @@ namespace Avalonia.Media
                 MiterLimit);
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             _invalidated?.Invoke(this, EventArgs.Empty);
             if(change.Property == BrushProperty)
@@ -207,13 +208,24 @@ namespace Avalonia.Media
         {
             if ((_invalidated == null || field != value) && field != null)
             {
-                InvalidatedWeakEvent.Unsubscribe(field, this);
+                if (_weakSubscriber != null)
+                    InvalidatedWeakEvent.Unsubscribe(field, _weakSubscriber);
                 field = null;
             }
 
             if (_invalidated != null && field != value && value is IAffectsRender affectsRender)
             {
-                InvalidatedWeakEvent.Subscribe(affectsRender, this);
+                if (_weakSubscriber == null)
+                {
+                    _weakSubscriber = new TargetWeakEventSubscriber<Pen, EventArgs>(
+                        this, static (target, _, ev, _) =>
+                        {
+                            if (ev == InvalidatedWeakEvent)
+                                target._invalidated?.Invoke(target, EventArgs.Empty);
+                        });
+                }
+
+                InvalidatedWeakEvent.Subscribe(affectsRender, _weakSubscriber);
                 field = affectsRender;
             }
         }
@@ -223,11 +235,5 @@ namespace Avalonia.Media
             UpdateSubscription(ref _subscribedToBrush, Brush);
             UpdateSubscription(ref _subscribedToDashes, DashStyle);
         }
-        
-        void IWeakEventSubscriber<EventArgs>.OnEvent(object? sender, WeakEvent ev, EventArgs e)
-        {
-            if (ev == InvalidatedWeakEvent) 
-                _invalidated?.Invoke(this, EventArgs.Empty);
-        }
     }
 }

src/Avalonia.Base/PropertyStore/BindingEntry.cs

@@ -18,19 +18,19 @@ namespace Avalonia.PropertyStore
     /// <typeparam name="T">The property type.</typeparam>
     internal class BindingEntry<T> : IBindingEntry, IPriorityValueEntry<T>, IObserver<BindingValue<T>>
     {
-        private readonly IAvaloniaObject _owner;
-        private IValueSink _sink;
+        private readonly AvaloniaObject _owner;
+        private ValueOwner<T> _sink;
         private IDisposable? _subscription;
         private bool _isSubscribed;
         private bool _batchUpdate;
         private Optional<T> _value;
 
         public BindingEntry(
-            IAvaloniaObject owner,
+            AvaloniaObject owner,
             StyledPropertyBase<T> property,
             IObservable<BindingValue<T>> source,
             BindingPriority priority,
-            IValueSink sink)
+            ValueOwner<T> sink)
         {
             _owner = owner;
             Property = property;
@@ -50,7 +50,7 @@ namespace Avalonia.PropertyStore
         {
             _batchUpdate = false;
 
-            if (_sink is ValueStore)
+            if (_sink.IsValueStore)
                 Start();
         }
 
@@ -113,16 +113,15 @@ namespace Avalonia.PropertyStore
             }
         }
 
-        public void Reparent(IValueSink sink) => _sink = sink;
+        public void Reparent(PriorityValue<T> parent) => _sink = new(parent);
 
         public void RaiseValueChanged(
-            IValueSink sink,
-            IAvaloniaObject owner,
+            AvaloniaObject owner,
             AvaloniaProperty property,
             Optional<object?> oldValue,
             Optional<object?> newValue)
         {
-            sink.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
+            owner.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
                 owner,
                 (AvaloniaProperty<T>)property,
                 oldValue.Cast<T>(),

src/Avalonia.Base/PropertyStore/ConstantValueEntry.cs

@@ -18,14 +18,14 @@ namespace Avalonia.PropertyStore
     /// <typeparam name="T">The property type.</typeparam>
     internal class ConstantValueEntry<T> : IPriorityValueEntry<T>, IConstantValueEntry
     {
-        private IValueSink _sink;
+        private ValueOwner<T> _sink;
         private Optional<T> _value;
 
         public ConstantValueEntry(
             StyledPropertyBase<T> property,
             T value,
             BindingPriority priority,
-            IValueSink sink)
+            ValueOwner<T> sink)
         {
             Property = property;
             _value = value;
@@ -37,7 +37,7 @@ namespace Avalonia.PropertyStore
             StyledPropertyBase<T> property,
             Optional<T> value,
             BindingPriority priority,
-            IValueSink sink)
+            ValueOwner<T> sink)
         {
             Property = property;
             _value = value;
@@ -62,17 +62,16 @@ namespace Avalonia.PropertyStore
             _sink.Completed(Property, this, oldValue);
         }
 
-        public void Reparent(IValueSink sink) => _sink = sink;
+        public void Reparent(PriorityValue<T> sink) => _sink = new(sink);
         public void Start() { }
 
         public void RaiseValueChanged(
-            IValueSink sink,
-            IAvaloniaObject owner,
+            AvaloniaObject owner,
             AvaloniaProperty property,
             Optional<object?> oldValue,
             Optional<object?> newValue)
         {
-            sink.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
+            owner.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
                 owner,
                 (AvaloniaProperty<T>)property,
                 oldValue.Cast<T>(),

src/Avalonia.Base/PropertyStore/IPriorityValueEntry.cs

@@ -5,7 +5,6 @@
     /// </summary>
     internal interface IPriorityValueEntry : IValue
     {
-        void Reparent(IValueSink sink);
     }
 
     /// <summary>
@@ -14,5 +13,6 @@
     /// <typeparam name="T">The property type.</typeparam>
     internal interface IPriorityValueEntry<T> : IPriorityValueEntry, IValue<T>
     {
+        void Reparent(PriorityValue<T> parent);
     }
 }

src/Avalonia.Base/PropertyStore/IValue.cs

@@ -11,8 +11,7 @@ namespace Avalonia.PropertyStore
         Optional<object?> GetValue();
         void Start();
         void RaiseValueChanged(
-            IValueSink sink,
-            IAvaloniaObject owner,
+            AvaloniaObject owner,
             AvaloniaProperty property,
             Optional<object?> oldValue,
             Optional<object?> newValue);

src/Avalonia.Base/PropertyStore/IValueSink.cs

@@ -1,17 +0,0 @@
-using Avalonia.Data;
-
-namespace Avalonia.PropertyStore
-{
-    /// <summary>
-    /// Represents an entity that can receive change notifications in a <see cref="ValueStore"/>.
-    /// </summary>
-    internal interface IValueSink
-    {
-        void ValueChanged<T>(AvaloniaPropertyChangedEventArgs<T> change);
-
-        void Completed<T>(
-            StyledPropertyBase<T> property,
-            IPriorityValueEntry entry,
-            Optional<T> oldValue);
-    }
-}

src/Avalonia.Base/PropertyStore/LocalValueEntry.cs

@@ -25,13 +25,12 @@ namespace Avalonia.PropertyStore
         public void Start() { }
 
         public void RaiseValueChanged(
-            IValueSink sink,
-            IAvaloniaObject owner,
+            AvaloniaObject owner,
             AvaloniaProperty property,
             Optional<object?> oldValue,
             Optional<object?> newValue)
         {
-            sink.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
+            owner.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
                 owner,
                 (AvaloniaProperty<T>)property,
                 oldValue.Cast<T>(),

src/Avalonia.Base/PropertyStore/PriorityValue.cs

@@ -1,10 +1,17 @@
 using System;
 using System.Collections.Generic;
-using System.ComponentModel;
 using Avalonia.Data;
 
 namespace Avalonia.PropertyStore
 {
+    /// <summary>
+    /// Represents an untyped interface to <see cref="PriorityValue{T}"/>.
+    /// </summary>
+    interface IPriorityValue : IValue
+    {
+        void UpdateEffectiveValue();
+    }
+
     /// <summary>
     /// Stores a set of prioritized values and bindings in a <see cref="ValueStore"/>.
     /// </summary>
@@ -16,10 +23,10 @@ namespace Avalonia.PropertyStore
     /// <see cref="IPriorityValueEntry{T}"/> entries (sorted first by priority and then in the order
     /// they were added) plus a local value.
     /// </remarks>
-    internal class PriorityValue<T> : IValue<T>, IValueSink, IBatchUpdate
+    internal class PriorityValue<T> : IPriorityValue, IValue<T>, IBatchUpdate
     {
-        private readonly IAvaloniaObject _owner;
-        private readonly IValueSink _sink;
+        private readonly AvaloniaObject _owner;
+        private readonly ValueStore _store;
         private readonly List<IPriorityValueEntry<T>> _entries = new List<IPriorityValueEntry<T>>();
         private readonly Func<IAvaloniaObject, T, T>? _coerceValue;
         private Optional<T> _localValue;
@@ -28,13 +35,13 @@ namespace Avalonia.PropertyStore
         private bool _batchUpdate;
 
         public PriorityValue(
-            IAvaloniaObject owner,
+            AvaloniaObject owner,
             StyledPropertyBase<T> property,
-            IValueSink sink)
+            ValueStore store)
         {
             _owner = owner;
             Property = property;
-            _sink = sink;
+            _store = store;
 
             if (property.HasCoercion)
             {
@@ -44,11 +51,11 @@ namespace Avalonia.PropertyStore
         }
 
         public PriorityValue(
-            IAvaloniaObject owner,
+            AvaloniaObject owner,
             StyledPropertyBase<T> property,
-            IValueSink sink,
+            ValueStore store,
             IPriorityValueEntry<T> existing)
-            : this(owner, property, sink)
+            : this(owner, property, store)
         {
             existing.Reparent(this);
             _entries.Add(existing);
@@ -75,9 +82,9 @@ namespace Avalonia.PropertyStore
         }
 
         public PriorityValue(
-            IAvaloniaObject owner,
+            AvaloniaObject owner,
             StyledPropertyBase<T> property,
-            IValueSink sink,
+            ValueStore sink,
             LocalValueEntry<T> existing)
             : this(owner, property, sink)
         {
@@ -148,7 +155,7 @@ namespace Avalonia.PropertyStore
             else
             {
                 var insert = FindInsertPoint(priority);
-                var entry = new ConstantValueEntry<T>(Property, value, priority, this);
+                var entry = new ConstantValueEntry<T>(Property, value, priority, new ValueOwner<T>(this));
                 _entries.Insert(insert, entry);
                 result = entry;
             }
@@ -165,7 +172,7 @@ namespace Avalonia.PropertyStore
 
         public BindingEntry<T> AddBinding(IObservable<BindingValue<T>> source, BindingPriority priority)
         {
-            var binding = new BindingEntry<T>(_owner, Property, source, priority, this);
+            var binding = new BindingEntry<T>(_owner, Property, source, priority, new(this));
             var insert = FindInsertPoint(binding.Priority);
             _entries.Insert(insert, binding);
 
@@ -186,13 +193,12 @@ namespace Avalonia.PropertyStore
         public void Start() => UpdateEffectiveValue(null);
 
         public void RaiseValueChanged(
-            IValueSink sink,
-            IAvaloniaObject owner,
+            AvaloniaObject owner,
             AvaloniaProperty property,
             Optional<object?> oldValue,
             Optional<object?> newValue)
         {
-            sink.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
+            owner.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
                 owner,
                 (AvaloniaProperty<T>)property,
                 oldValue.Cast<T>(),
@@ -200,7 +206,7 @@ namespace Avalonia.PropertyStore
                 Priority));
         }
 
-        void IValueSink.ValueChanged<TValue>(AvaloniaPropertyChangedEventArgs<TValue> change)
+        public void ValueChanged<TValue>(AvaloniaPropertyChangedEventArgs<TValue> change)
         {
             if (change.Priority == BindingPriority.LocalValue)
             {
@@ -213,22 +219,15 @@ namespace Avalonia.PropertyStore
             }
         }
 
-        void IValueSink.Completed<TValue>(
-            StyledPropertyBase<TValue> property,
-            IPriorityValueEntry entry,
-            Optional<TValue> oldValue)
+        public void Completed(IPriorityValueEntry entry, Optional<T> oldValue)
         {
             _entries.Remove((IPriorityValueEntry<T>)entry);
-
-            if (oldValue is Optional<T> o)
-            {
-                UpdateEffectiveValue(new AvaloniaPropertyChangedEventArgs<T>(
-                    _owner,
-                    Property,
-                    o,
-                    default,
-                    entry.Priority));
-            }
+            UpdateEffectiveValue(new AvaloniaPropertyChangedEventArgs<T>(
+                _owner,
+                Property,
+                oldValue,
+                default,
+                entry.Priority));
         }
 
         private int FindInsertPoint(BindingPriority priority)
@@ -308,7 +307,7 @@ namespace Avalonia.PropertyStore
                 var old = _value;
                 _value = value;
 
-                _sink.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
+                _store.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
                     _owner,
                     Property,
                     old,
@@ -319,7 +318,7 @@ namespace Avalonia.PropertyStore
             {
                 change.MarkNonEffectiveValue();
                 change.SetOldValue(default);
-                _sink.ValueChanged(change);
+                _store.ValueChanged(change);
             }
         }
     }

src/Avalonia.Base/PropertyStore/ValueOwner.cs

@@ -0,0 +1,45 @@
+using Avalonia.Data;
+
+namespace Avalonia.PropertyStore
+{
+    /// <summary>
+    /// Represents a union type of <see cref="ValueStore"/> and <see cref="PriorityValue{T}"/>,
+    /// which are the valid owners of a value store <see cref="IValue"/>.
+    /// </summary>
+    /// <typeparam name="T">The value type.</typeparam>
+    internal readonly struct ValueOwner<T>
+    {
+        private readonly ValueStore? _store;
+        private readonly PriorityValue<T>? _priorityValue;
+
+        public ValueOwner(ValueStore o)
+        {
+            _store = o;
+            _priorityValue = null;
+        }
+
+        public ValueOwner(PriorityValue<T> v)
+        {
+            _store = null;
+            _priorityValue = v;
+        }
+
+        public bool IsValueStore => _store is not null;
+
+        public void Completed(StyledPropertyBase<T> property, IPriorityValueEntry entry, Optional<T> oldValue)
+        {
+            if (_store is not null)
+                _store?.Completed(property, entry, oldValue);
+            else
+                _priorityValue!.Completed(entry, oldValue);
+        }
+
+        public void ValueChanged(AvaloniaPropertyChangedEventArgs<T> e)
+        {
+            if (_store is not null)
+                _store?.ValueChanged(e);
+            else
+                _priorityValue!.ValueChanged(e);
+        }
+    }
+}

src/Avalonia.Base/Reactive/AvaloniaPropertyBindingObservable.cs

@@ -51,7 +51,7 @@ namespace Avalonia.Reactive
             {
                 if (e is AvaloniaPropertyChangedEventArgs<T> typedArgs)
                 {
-                    var newValue = e.Sender.GetValue(typedArgs.Property);
+                    var newValue = e.Sender.GetValue<T>(typedArgs.Property);
 
                     if (!_value.HasValue || !EqualityComparer<T>.Default.Equals(newValue, _value.Value))
                     {

src/Avalonia.Base/Reactive/AvaloniaPropertyObservable.cs

@@ -49,23 +49,31 @@ namespace Avalonia.Reactive
         {
             if (e.Property == _property)
             {
-                T newValue;
-
-                if (e is AvaloniaPropertyChangedEventArgs<T> typed)
+                if (e.Sender is AvaloniaObject ao)
                 {
-                    newValue = typed.Sender.GetValue(typed.Property);
+                    T newValue;
+
+                    if (e is AvaloniaPropertyChangedEventArgs<T> typed)
+                    {
+                        newValue = AvaloniaObjectExtensions.GetValue(ao, typed.Property);
+                    }
+                    else
+                    {
+                        newValue = (T)e.Sender.GetValue(e.Property)!;
+                    }
+
+                    if (!_value.HasValue ||
+                        !EqualityComparer<T>.Default.Equals(newValue, _value.Value))
+                    {
+                        _value = newValue;
+                        PublishNext(_value.Value!);
+                    }
                 }
                 else
                 {
-                    newValue = (T)e.Sender.GetValue(e.Property)!;
+                    throw new NotSupportedException("Custom implementations of IAvaloniaObject not supported.");
                 }
 
-                if (!_value.HasValue ||
-                    !EqualityComparer<T>.Default.Equals(newValue, _value.Value))
-                {
-                    _value = newValue;
-                    PublishNext(_value.Value!);
-                }
             }
         }
     }

src/Avalonia.Base/StyledElement.cs

@@ -467,7 +467,12 @@ namespace Avalonia
         /// <param name="parent">The parent.</param>
         void ISetInheritanceParent.SetParent(IAvaloniaObject? parent)
         {
-            InheritanceParent = parent;
+            InheritanceParent = parent switch
+            {
+                AvaloniaObject ao => ao,
+                null => null,
+                _ => throw new NotSupportedException("Custom implementations of IAvaloniaObject not supported.")
+            };
         }
 
         void IStyleable.StyleApplied(IStyleInstance instance)

src/Avalonia.Base/StyledPropertyBase.cs

@@ -2,6 +2,7 @@ using System;
 using System.Diagnostics;
 using Avalonia.Data;
 using Avalonia.Reactive;
+using Avalonia.Styling;
 using Avalonia.Utilities;
 
 namespace Avalonia
@@ -158,12 +159,6 @@ namespace Avalonia
             base.OverrideMetadata(type, metadata);
         }
 
-        /// <inheritdoc/>
-        public override void Accept<TData>(IAvaloniaPropertyVisitor<TData> visitor, ref TData data)
-        {
-            visitor.Visit(this, ref data);
-        }
-
         /// <summary>
         /// Gets the string representation of the property.
         /// </summary>
@@ -177,19 +172,19 @@ namespace Avalonia
         object? IStyledPropertyAccessor.GetDefaultValue(Type type) => GetDefaultBoxedValue(type);
 
         /// <inheritdoc/>
-        internal override void RouteClearValue(IAvaloniaObject o)
+        internal override void RouteClearValue(AvaloniaObject o)
         {
             o.ClearValue<TValue>(this);
         }
 
         /// <inheritdoc/>
-        internal override object? RouteGetValue(IAvaloniaObject o)
+        internal override object? RouteGetValue(AvaloniaObject o)
         {
             return o.GetValue<TValue>(this);
         }
 
         /// <inheritdoc/>
-        internal override object? RouteGetBaseValue(IAvaloniaObject o, BindingPriority maxPriority)
+        internal override object? RouteGetBaseValue(AvaloniaObject o, BindingPriority maxPriority)
         {
             var value = o.GetBaseValue<TValue>(this, maxPriority);
             return value.HasValue ? value.Value : AvaloniaProperty.UnsetValue;
@@ -197,7 +192,7 @@ namespace Avalonia
 
         /// <inheritdoc/>
         internal override IDisposable? RouteSetValue(
-            IAvaloniaObject o,
+            AvaloniaObject o,
             object? value,
             BindingPriority priority)
         {
@@ -221,7 +216,7 @@ namespace Avalonia
 
         /// <inheritdoc/>
         internal override IDisposable RouteBind(
-            IAvaloniaObject o,
+            AvaloniaObject o,
             IObservable<BindingValue<object?>> source,
             BindingPriority priority)
         {
@@ -232,11 +227,36 @@ namespace Avalonia
         /// <inheritdoc/>
         internal override void RouteInheritanceParentChanged(
             AvaloniaObject o,
-            IAvaloniaObject? oldParent)
+            AvaloniaObject? oldParent)
         {
             o.InheritanceParentChanged(this, oldParent);
         }
 
+        internal override ISetterInstance CreateSetterInstance(IStyleable target, object? value)
+        {
+            if (value is IBinding binding)
+            {
+                return new PropertySetterBindingInstance<TValue>(
+                    target,
+                    this,
+                    binding);
+            }
+            else if (value is ITemplate template && !typeof(ITemplate).IsAssignableFrom(PropertyType))
+            {
+                return new PropertySetterLazyInstance<TValue>(
+                    target,
+                    this,
+                    () => (TValue)template.Build());
+            }
+            else
+            {
+                return new PropertySetterInstance<TValue>(
+                    target,
+                    this,
+                    (TValue)value!);
+            }
+        }
+
         private object? GetDefaultBoxedValue(Type type)
         {
             _ = type ?? throw new ArgumentNullException(nameof(type));

src/Avalonia.Base/Styling/Setter.cs

@@ -16,7 +16,7 @@ namespace Avalonia.Styling
     /// A <see cref="Setter"/> is used to set a <see cref="AvaloniaProperty"/> value on a
     /// <see cref="AvaloniaObject"/> depending on a condition.
     /// </remarks>
-    public class Setter : ISetter, IAnimationSetter, IAvaloniaPropertyVisitor<Setter.SetterVisitorData>
+    public class Setter : ISetter, IAnimationSetter
     {
         private object? _value;
 
@@ -68,68 +68,7 @@ namespace Avalonia.Styling
                 throw new InvalidOperationException("Setter.Property must be set.");
             }
 
-            var data = new SetterVisitorData
-            {
-                target = target,
-                value = Value,
-            };
-
-            Property.Accept(this, ref data);
-            return data.result!;
-        }
-
-        void IAvaloniaPropertyVisitor<SetterVisitorData>.Visit<T>(
-            StyledPropertyBase<T> property,
-            ref SetterVisitorData data)
-        {
-            if (data.value is IBinding binding)
-            {
-                data.result = new PropertySetterBindingInstance<T>(
-                    data.target,
-                    property,
-                    binding);
-            }
-            else if (data.value is ITemplate template && !typeof(ITemplate).IsAssignableFrom(property.PropertyType))
-            {
-                data.result = new PropertySetterLazyInstance<T>(
-                    data.target,
-                    property,
-                    () => (T)template.Build());
-            }
-            else
-            {
-                data.result = new PropertySetterInstance<T>(
-                    data.target,
-                    property,
-                    (T)data.value!);
-            }
-        }
-
-        void IAvaloniaPropertyVisitor<SetterVisitorData>.Visit<T>(
-            DirectPropertyBase<T> property,
-            ref SetterVisitorData data)
-        {
-            if (data.value is IBinding binding)
-            {
-                data.result = new PropertySetterBindingInstance<T>(
-                    data.target,
-                    property,
-                    binding);
-            }
-            else if (data.value is ITemplate template && !typeof(ITemplate).IsAssignableFrom(property.PropertyType))
-            {
-                data.result = new PropertySetterLazyInstance<T>(
-                    data.target,
-                    property,
-                    () => (T)template.Build());
-            }
-            else
-            {
-                data.result = new PropertySetterInstance<T>(
-                    data.target,
-                    property,
-                    (T)data.value!);
-            }
+            return Property.CreateSetterInstance(target, Value);
         }
 
         private struct SetterVisitorData

src/Avalonia.Base/Threading/IDispatcher.cs

@@ -26,15 +26,6 @@ namespace Avalonia.Threading
         /// <param name="priority">The priority with which to invoke the method.</param>
         void Post(Action action, DispatcherPriority priority = default);
 
-        /// <summary>
-        /// Posts an action that will be invoked on the dispatcher thread.
-        /// </summary>
-        /// <typeparam name="T">type of argument</typeparam>
-        /// <param name="action">The method to call.</param>
-        /// <param name="arg">The argument of method to call.</param>
-        /// <param name="priority">The priority with which to invoke the method.</param>
-        void Post<T>(Action<T> action, T arg, DispatcherPriority priority = default);
-
         /// <summary>
         /// Invokes a action on the dispatcher thread.
         /// </summary>
@@ -43,14 +34,6 @@ namespace Avalonia.Threading
         /// <returns>A task that can be used to track the method's execution.</returns>
         Task InvokeAsync(Action action, DispatcherPriority priority = default);
 
-        /// <summary>
-        /// Invokes a method on the dispatcher thread.
-        /// </summary>
-        /// <param name="function">The method.</param>
-        /// <param name="priority">The priority with which to invoke the method.</param>
-        /// <returns>A task that can be used to track the method's execution.</returns>
-        Task<TResult> InvokeAsync<TResult>(Func<TResult> function, DispatcherPriority priority = default);
-
         /// <summary>
         /// Queues the specified work to run on the dispatcher thread and returns a proxy for the
         /// task returned by <paramref name="function"/>.
@@ -59,14 +42,5 @@ namespace Avalonia.Threading
         /// <param name="priority">The priority with which to invoke the method.</param>
         /// <returns>A task that represents a proxy for the task returned by <paramref name="function"/>.</returns>
         Task InvokeAsync(Func<Task> function, DispatcherPriority priority = default);
-
-        /// <summary>
-        /// Queues the specified work to run on the dispatcher thread and returns a proxy for the
-        /// task returned by <paramref name="function"/>.
-        /// </summary>
-        /// <param name="function">The work to execute asynchronously.</param>
-        /// <param name="priority">The priority with which to invoke the method.</param>
-        /// <returns>A task that represents a proxy for the task returned by <paramref name="function"/>.</returns>
-        Task<TResult> InvokeAsync<TResult>(Func<Task<TResult>> function, DispatcherPriority priority = default);
     }
 }

src/Avalonia.Base/Utilities/IAvaloniaPropertyVisitor.cs

@@ -1,32 +0,0 @@
-namespace Avalonia.Utilities
-{
-    /// <summary>
-    /// A visitor to resolve an untyped <see cref="AvaloniaProperty"/> to a typed property.
-    /// </summary>
-    /// <typeparam name="TData">The type of user data passed.</typeparam>
-    /// <remarks>
-    /// Pass an instance that implements this interface to
-    /// <see cref="AvaloniaProperty.Accept{TData}(IAvaloniaPropertyVisitor{TData}, ref TData)"/>
-    /// in order to resolve un untyped <see cref="AvaloniaProperty"/> to a typed
-    /// <see cref="StyledPropertyBase{TValue}"/> or <see cref="DirectPropertyBase{TValue}"/>.
-    /// </remarks>
-    public interface IAvaloniaPropertyVisitor<TData>
-        where TData : struct
-    {
-        /// <summary>
-        /// Called when the property is a styled property.
-        /// </summary>
-        /// <typeparam name="T">The property value type.</typeparam>
-        /// <param name="property">The property.</param>
-        /// <param name="data">The user data.</param>
-        void Visit<T>(StyledPropertyBase<T> property, ref TData data);
-
-        /// <summary>
-        /// Called when the property is a direct property.
-        /// </summary>
-        /// <typeparam name="T">The property value type.</typeparam>
-        /// <param name="property">The property.</param>
-        /// <param name="data">The user data.</param>
-        void Visit<T>(DirectPropertyBase<T> property, ref TData data);
-    }
-}

src/Avalonia.Base/Utilities/IWeakEventSubscriber.cs

@@ -9,4 +9,31 @@ namespace Avalonia.Utilities;
 public interface IWeakEventSubscriber<in TEventArgs> where TEventArgs : EventArgs
 {
     void OnEvent(object? sender, WeakEvent ev, TEventArgs e);
-}
+}
+
+public sealed class WeakEventSubscriber<TEventArgs> : IWeakEventSubscriber<TEventArgs> where TEventArgs : EventArgs 
+{
+    public event Action<object?, WeakEvent, TEventArgs>? Event;
+
+    void IWeakEventSubscriber<TEventArgs>.OnEvent(object? sender, WeakEvent ev, TEventArgs e)
+    {
+        Event?.Invoke(sender, ev, e);
+    }
+}
+
+public sealed class TargetWeakEventSubscriber<TTarget, TEventArgs> : IWeakEventSubscriber<TEventArgs> where TEventArgs : EventArgs
+{
+    private readonly TTarget _target;
+    private readonly Action<TTarget, object?, WeakEvent, TEventArgs> _dispatchFunc;
+
+    public TargetWeakEventSubscriber(TTarget target, Action<TTarget, object?, WeakEvent, TEventArgs> dispatchFunc)
+    {
+        _target = target;
+        _dispatchFunc = dispatchFunc;
+    }
+
+    void IWeakEventSubscriber<TEventArgs>.OnEvent(object? sender, WeakEvent ev, TEventArgs e)
+    {
+        _dispatchFunc(_target, sender, ev, e);
+    }
+}

src/Avalonia.Base/Utilities/WeakEvent.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection;
 using System.Runtime.CompilerServices;
@@ -36,7 +37,7 @@ public class WeakEvent<TSender, TEventArgs> : WeakEvent where TEventArgs : Event
     {
         if (!_subscriptions.TryGetValue(target, out var subscription))
             _subscriptions.Add(target, subscription = new Subscription(this, target));
-        subscription.Add(new WeakReference<IWeakEventSubscriber<TEventArgs>>(subscriber));
+        subscription.Add(subscriber);
     }
 
     public void Unsubscribe(TSender target, IWeakEventSubscriber<TEventArgs> subscriber)
@@ -51,11 +52,59 @@ public class WeakEvent<TSender, TEventArgs> : WeakEvent where TEventArgs : Event
         private readonly TSender _target;
         private readonly Action _compact;
 
-        private WeakReference<IWeakEventSubscriber<TEventArgs>>?[] _data =
-            new WeakReference<IWeakEventSubscriber<TEventArgs>>[16];
-        private int _count;
+        struct Entry
+        {
+            WeakReference<IWeakEventSubscriber<TEventArgs>>? _reference;
+            int _hashCode;
+
+            public Entry(IWeakEventSubscriber<TEventArgs> r)
+            {
+                if (r == null)
+                {
+                    _reference = null;
+                    _hashCode = 0;
+                    return;
+                }
+
+                _hashCode = r.GetHashCode();
+                _reference = new WeakReference<IWeakEventSubscriber<TEventArgs>>(r);
+            }
+
+            public bool IsEmpty
+            {
+                get
+                {
+                    if (_reference == null)
+                        return true;
+                    if (_reference.TryGetTarget(out _))
+                        return false;
+                    _reference = null;
+                    return true;
+                }
+            }
+
+            public bool TryGetTarget([MaybeNullWhen(false)]out IWeakEventSubscriber<TEventArgs> target)
+            {
+                if (_reference == null)
+                {
+                    target = null!;
+                    return false;
+                }
+                return _reference.TryGetTarget(out target);
+            }
+
+            public bool Equals(IWeakEventSubscriber<TEventArgs> r)
+            {
+                if (_reference == null || r.GetHashCode() != _hashCode)
+                    return false;
+                return _reference.TryGetTarget(out var target) && target == r;
+            }
+        }
+
         private readonly Action _unsubscribe;
+        private readonly WeakHashList<IWeakEventSubscriber<TEventArgs>> _list = new();
         private bool _compactScheduled;
+        private bool _destroyed;
 
         public Subscription(WeakEvent<TSender, TEventArgs> ev, TSender target)
         {
@@ -67,48 +116,27 @@ public class WeakEvent<TSender, TEventArgs> : WeakEvent where TEventArgs : Event
 
         void Destroy()
         {
+            if(_destroyed)
+                return;
+            _destroyed = true;
             _unsubscribe();
             _ev._subscriptions.Remove(_target);
         }
 
-        public void Add(WeakReference<IWeakEventSubscriber<TEventArgs>> s)
-        {
-            if (_count == _data.Length)
-            {
-                //Extend capacity
-                var extendedData = new WeakReference<IWeakEventSubscriber<TEventArgs>>?[_data.Length * 2];
-                Array.Copy(_data, extendedData, _data.Length);
-                _data = extendedData;
-            }
-
-            _data[_count] = s;
-            _count++;
-        }
+        public void Add(IWeakEventSubscriber<TEventArgs> s) => _list.Add(s);
 
         public void Remove(IWeakEventSubscriber<TEventArgs> s)
         {
-            var removed = false;
-
-            for (int c = 0; c < _count; ++c)
-            {
-                var reference = _data[c];
-
-                if (reference != null && reference.TryGetTarget(out var instance) && instance == s)
-                {
-                    _data[c] = null;
-                    removed = true;
-                }
-            }
-
-            if (removed)
-            {
+            _list.Remove(s);
+            if(_list.IsEmpty)
+                Destroy();
+            else if(_list.NeedCompact && _compactScheduled)
                 ScheduleCompact();
-            }
         }
 
         void ScheduleCompact()
         {
-            if(_compactScheduled)
+            if(_compactScheduled || _destroyed)
                 return;
             _compactScheduled = true;
             Dispatcher.UIThread.Post(_compact, DispatcherPriority.Background);
@@ -116,43 +144,27 @@ public class WeakEvent<TSender, TEventArgs> : WeakEvent where TEventArgs : Event
         
         void Compact()
         {
+            if(!_compactScheduled)
+                return;
             _compactScheduled = false;
-            int empty = -1;
-            for (var c = 0; c < _count; c++)
-            {
-                var r = _data[c];
-                //Mark current index as first empty
-                if (r == null && empty == -1)
-                    empty = c;
-                //If current element isn't null and we have an empty one
-                if (r != null && empty != -1)
-                {
-                    _data[c] = null;
-                    _data[empty] = r;
-                    empty++;
-                }
-            }
-
-            if (empty != -1)
-                _count = empty;
-            if (_count == 0)
+            _list.Compact();
+            if (_list.IsEmpty)
                 Destroy();
         }
 
         void OnEvent(object? sender, TEventArgs eventArgs)
         {
-            var needCompact = false;
-            for (var c = 0; c < _count; c++)
+            var alive = _list.GetAlive();
+            if(alive == null)
+                Destroy();
+            else
             {
-                var r = _data[c];
-                if (r?.TryGetTarget(out var sub) == true)
-                    sub!.OnEvent(_target, _ev, eventArgs);
-                else
-                    needCompact = true;
+                foreach(var item in alive.Span)
+                    item.OnEvent(_target, _ev, eventArgs);
+                WeakHashList<IWeakEventSubscriber<TEventArgs>>.ReturnToSharedPool(alive);
+                if(_list.NeedCompact && !_compactScheduled)
+                    ScheduleCompact();
             }
-
-            if (needCompact)
-                ScheduleCompact();
         }
     }
 

src/Avalonia.Base/Utilities/WeakHashList.cs

@@ -0,0 +1,238 @@
+using System;
+using System.Collections.Generic;
+using Avalonia.Collections.Pooled;
+
+namespace Avalonia.Utilities;
+
+internal class WeakHashList<T> where T : class
+{
+    private struct Key
+    {
+        public WeakReference<T>? Weak;
+        public T? Strong;
+        public int HashCode;
+
+        public static Key MakeStrong(T r) => new()
+        {
+            HashCode = r.GetHashCode(),
+            Strong = r
+        };
+
+        public static Key MakeWeak(T r) => new()
+        {
+            HashCode = r.GetHashCode(),
+            Weak = new WeakReference<T>(r)
+        };
+
+        public override int GetHashCode() => HashCode;
+    }
+
+    class KeyComparer : IEqualityComparer<Key>
+    {
+        public bool Equals(Key x, Key y)
+        {
+            if (x.HashCode != y.HashCode)
+                return false;
+            if (x.Strong != null)
+            {
+                if (y.Strong != null)
+                    return x.Strong == y.Strong;
+                if (y.Weak == null)
+                    return false;
+                return y.Weak.TryGetTarget(out var weakTarget) && weakTarget == x.Strong;
+            }
+            else if (y.Strong != null)
+            {
+                if (x.Weak == null)
+                    return false;
+                return x.Weak.TryGetTarget(out var weakTarget) && weakTarget == y.Strong;
+            }
+            else
+            {
+                if (x.Weak == null || x.Weak.TryGetTarget(out var xTarget) == false)
+                    return y.Weak?.TryGetTarget(out _) != true;
+                return y.Weak?.TryGetTarget(out var yTarget) == true && xTarget == yTarget;
+            }
+        }
+
+        public int GetHashCode(Key obj) => obj.HashCode;
+        public static KeyComparer Instance = new();
+    }
+
+    Dictionary<Key, int>? _dic;
+    WeakReference<T>?[]? _arr;
+    int _arrCount;
+    
+    public bool IsEmpty => _dic == null || _dic.Count == 0;
+    public bool NeedCompact { get; private set; }
+    
+    public void Add(T item)
+    {
+        if (_dic != null)
+        {
+            var strongKey = Key.MakeStrong(item);
+            if (_dic.TryGetValue(strongKey, out var cnt))
+                _dic[strongKey] = cnt + 1;
+            else
+                _dic[Key.MakeWeak(item)] = 1;
+            return;
+        }
+
+        if (_arr == null)
+            _arr = new WeakReference<T>[8];
+
+        if (_arrCount < _arr.Length)
+        {
+            _arr[_arrCount] = new WeakReference<T>(item);
+            _arrCount++;
+            return;
+        }
+
+        // Check if something is dead
+        for (var c = 0; c < _arrCount; c++)
+        {
+            if (_arr[c]!.TryGetTarget(out _) == false)
+            {
+                _arr[c] = new WeakReference<T>(item);
+                return;
+            }
+        }
+
+        _dic = new Dictionary<Key, int>(KeyComparer.Instance);
+        foreach (var existing in _arr)
+        {
+            if (existing!.TryGetTarget(out var target))
+                Add(target);
+        }
+        
+        Add(item);
+
+        _arr = null;
+    }
+
+    public void Remove(T item)
+    {
+        if (_arr != null)
+        {
+            for (var c = 0; c < _arr.Length; c++)
+            {
+                if (_arr[c]?.TryGetTarget(out var target) == true && target == item)
+                {
+                    _arr[c] = null;
+                    Compact();
+                    return;
+                }
+            }
+        }
+        else if (_dic != null)
+        {
+            var strongKey = Key.MakeStrong(item);
+            
+            if (_dic.TryGetValue(strongKey, out var cnt))
+            {
+                if (cnt > 1)
+                {
+                    _dic[strongKey] = cnt - 1;
+                    return;
+                }
+            }
+
+            _dic.Remove(strongKey);
+        }
+    }
+
+    private void ArrCompact()
+    {
+        if (_arr != null)
+        {
+            int empty = -1;
+            for (var c = 0; c < _arrCount; c++)
+            {
+                var r = _arr[c];
+                //Mark current index as first empty
+                if (r == null && empty == -1)
+                    empty = c;
+                //If current element isn't null and we have an empty one
+                if (r != null && empty != -1)
+                {
+                    _arr[c] = null;
+                    _arr[empty] = r;
+                    empty++;
+                }
+            }
+
+            if (empty != -1)
+                _arrCount = empty;
+        }
+    }
+    
+    public void Compact()
+    {
+        if (_dic != null)
+        {
+            PooledList<Key>? toRemove = null;
+            foreach (var kvp in _dic)
+            {
+                if (kvp.Key.Weak?.TryGetTarget(out _) != true)
+                    (toRemove ??= new PooledList<Key>()).Add(kvp.Key);
+            }
+
+            if (toRemove != null)
+            {
+                foreach (var k in toRemove)
+                    _dic.Remove(k);
+                toRemove.Dispose();
+            }
+        }
+    }
+
+    private static readonly Stack<PooledList<T>> s_listPool = new();
+
+    public static void ReturnToSharedPool(PooledList<T> list)
+    {
+        list.Clear();
+        s_listPool.Push(list);
+    }
+    
+    public PooledList<T>? GetAlive(Func<PooledList<T>>? factory = null)
+    {
+        PooledList<T>? pooled = null;
+        if (_arr != null)
+        {
+            bool needCompact = false;
+            for (var c = 0; c < _arrCount; c++)
+            {
+                if (_arr[c]?.TryGetTarget(out var target) == true)
+                    (pooled ??= factory?.Invoke()
+                                ?? (s_listPool.Count > 0
+                                    ? s_listPool.Pop()
+                                    : new PooledList<T>())).Add(target!);
+                else
+                {
+                    _arr[c] = null;
+                    needCompact = true;
+                }
+            }
+            if(needCompact)
+                ArrCompact();
+            return pooled;
+        }
+        if (_dic != null)
+        {
+            
+            foreach (var kvp in _dic)
+            {
+                if (kvp.Key.Weak?.TryGetTarget(out var target) == true)
+                    (pooled ??= factory?.Invoke()
+                                ?? (s_listPool.Count > 0
+                                    ? s_listPool.Pop()
+                                    : new PooledList<T>()))
+                        .Add(target!);
+                else
+                    NeedCompact = true;
+            }
+        }
+
+        return pooled;
+    }
+}

src/Avalonia.Base/ValueStore.cs

@@ -21,16 +21,15 @@ namespace Avalonia
     /// - For a single binding it will be an instance of <see cref="BindingEntry{T}"/>
     /// - For all other cases it will be an instance of <see cref="PriorityValue{T}"/>
     /// </remarks>
-    internal class ValueStore : IValueSink
+    internal class ValueStore
     {
         private readonly AvaloniaObject _owner;
-        private readonly IValueSink _sink;
         private readonly AvaloniaPropertyValueStore<IValue> _values;
         private BatchUpdate? _batchUpdate;
 
         public ValueStore(AvaloniaObject owner)
         {
-            _sink = _owner = owner;
+            _owner = owner;
             _values = new AvaloniaPropertyValueStore<IValue>();
         }
 
@@ -122,7 +121,7 @@ namespace Avalonia
                 }
                 else
                 {
-                    var entry = new ConstantValueEntry<T>(property, value, priority, this);
+                    var entry = new ConstantValueEntry<T>(property, value, priority, new(this));
                     AddValue(property, entry);
                     NotifyValueChanged<T>(property, default, value, priority);
                     result = entry;
@@ -151,7 +150,7 @@ namespace Avalonia
             }
             else
             {
-                var entry = new BindingEntry<T>(_owner, property, source, priority, this);
+                var entry = new BindingEntry<T>(_owner, property, source, priority, new(this));
                 AddValue(property, entry);
                 return entry;
             }
@@ -187,7 +186,7 @@ namespace Avalonia
                         // so there's no way to mark them for removal at the end of a batch update. Instead convert
                         // them to a constant value entry with Unset priority in the event of a local value being
                         // cleared during a batch update.
-                        var sentinel = new ConstantValueEntry<T>(property, Optional<T>.Empty, BindingPriority.Unset, _sink);
+                        var sentinel = new ConstantValueEntry<T>(property, Optional<T>.Empty, BindingPriority.Unset, new(this));
                         _values.SetValue(property, sentinel);
                     }
 
@@ -196,11 +195,11 @@ namespace Avalonia
             }
         }
 
-        public void CoerceValue<T>(StyledPropertyBase<T> property)
+        public void CoerceValue(AvaloniaProperty property)
         {
             if (TryGetValue(property, out var slot))
             {
-                if (slot is PriorityValue<T> p)
+                if (slot is IPriorityValue p)
                 {
                     p.UpdateEffectiveValue();
                 }
@@ -222,7 +221,7 @@ namespace Avalonia
             return null;
         }
 
-        void IValueSink.ValueChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        public void ValueChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
         {
             if (_batchUpdate is object)
             {
@@ -233,11 +232,11 @@ namespace Avalonia
             }
             else
             {
-                _sink.ValueChanged(change);
+                _owner.ValueChanged(change);
             }
         }
 
-        void IValueSink.Completed<T>(
+        public void Completed<T>(
             StyledPropertyBase<T> property,
             IPriorityValueEntry entry,
             Optional<T> oldValue)
@@ -248,7 +247,7 @@ namespace Avalonia
                 if (_batchUpdate is null)
                 {
                     _values.Remove(property);
-                    _sink.Completed(property, entry, oldValue);
+                    _owner.Completed(property, entry, oldValue);
                 }
                 else
                 {
@@ -352,7 +351,7 @@ namespace Avalonia
         {
             if (_batchUpdate is null)
             {
-                _sink.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
+                _owner.ValueChanged(new AvaloniaPropertyChangedEventArgs<T>(
                     _owner,
                     property,
                     oldValue,
@@ -451,7 +450,7 @@ namespace Avalonia
                             };
 
                             // Call _sink.ValueChanged with an appropriately typed AvaloniaPropertyChangedEventArgs<T>.
-                            slot.RaiseValueChanged(_owner._sink, _owner._owner, entry.property, oldValue, newValue);
+                            slot.RaiseValueChanged(_owner._owner, entry.property, oldValue, newValue);
 
                             // During batch update values can't be removed immediately because they're needed to raise
                             // the _sink.ValueChanged notification. They instead mark themselves for removal by setting

src/Avalonia.Base/Visual.cs

@@ -97,12 +97,18 @@ namespace Avalonia
         /// </summary>
         public static readonly StyledProperty<int> ZIndexProperty =
             AvaloniaProperty.Register<Visual, int>(nameof(ZIndex));
+        
+        private static readonly WeakEvent<IAffectsRender, EventArgs> InvalidatedWeakEvent =
+            WeakEvent.Register<IAffectsRender>(
+                (s, h) => s.Invalidated += h,
+                (s, h) => s.Invalidated -= h);
 
         private Rect _bounds;
         private TransformedBounds? _transformedBounds;
         private IRenderRoot? _visualRoot;
         private IVisual? _visualParent;
         private bool _hasMirrorTransform;
+        private TargetWeakEventSubscriber<Visual, EventArgs>? _affectsRenderWeakSubscriber;
 
         /// <summary>
         /// Initializes static members of the <see cref="Visual"/> class.
@@ -369,12 +375,21 @@ namespace Avalonia
                 {
                     if (e.OldValue is IAffectsRender oldValue)
                     {
-                        WeakEventHandlerManager.Unsubscribe<EventArgs, T>(oldValue, nameof(oldValue.Invalidated), sender.AffectsRenderInvalidated);
+                        if (sender._affectsRenderWeakSubscriber != null)
+                            InvalidatedWeakEvent.Unsubscribe(oldValue, sender._affectsRenderWeakSubscriber);
                     }
 
                     if (e.NewValue is IAffectsRender newValue)
                     {
-                        WeakEventHandlerManager.Subscribe<IAffectsRender, EventArgs, T>(newValue, nameof(newValue.Invalidated), sender.AffectsRenderInvalidated);
+                        if (sender._affectsRenderWeakSubscriber == null)
+                        {
+                            sender._affectsRenderWeakSubscriber = new TargetWeakEventSubscriber<Visual, EventArgs>(
+                                sender, static (target, _, _, _) =>
+                                {
+                                    target.InvalidateVisual();
+                                });
+                        }
+                        InvalidatedWeakEvent.Subscribe(newValue, sender._affectsRenderWeakSubscriber);
                     }
 
                     sender.InvalidateVisual();
@@ -625,8 +640,6 @@ namespace Avalonia
             OnVisualParentChanged(old, value);
         }
 
-        private void AffectsRenderInvalidated(object? sender, EventArgs e) => InvalidateVisual();
-
         /// <summary>
         /// Called when the <see cref="VisualChildren"/> collection changes.
         /// </summary>

src/Avalonia.Controls.DataGrid/ApiCompatBaseline.txt

@@ -1 +1,4 @@
-Total Issues: 0
+Compat issues with assembly Avalonia.Controls.DataGrid:
+MembersMustExist : Member 'protected void Avalonia.Controls.DataGridCheckBoxColumn.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.DataGridTextColumn.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
+Total Issues: 2

src/Avalonia.Controls.DataGrid/DataGridCheckBoxColumn.cs

@@ -46,7 +46,7 @@ namespace Avalonia.Controls
             set => SetValue(IsThreeStateProperty, value);
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 

src/Avalonia.Controls.DataGrid/DataGridColumn.cs

@@ -192,14 +192,14 @@ namespace Avalonia.Controls
             set => SetValue(IsVisibleProperty, value);
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == IsVisibleProperty)
             {
                 OwningGrid?.OnColumnVisibleStateChanging(this);
-                var isVisible = change.NewValue.GetValueOrDefault<bool>();
+                var isVisible = change.GetNewValue<bool>();
 
                 if (_headerCell != null)
                 {

src/Avalonia.Controls.DataGrid/DataGridRow.cs

@@ -1062,7 +1062,7 @@ namespace Avalonia.Controls
         }
         
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             if (change.Property == DataContextProperty)
             {

src/Avalonia.Controls.DataGrid/DataGridTextColumn.cs

@@ -119,7 +119,7 @@ namespace Avalonia.Controls
             set => SetValue(ForegroundProperty, value);
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 

src/Avalonia.Controls/ApiCompatBaseline.txt

@@ -1,11 +1,17 @@
 Compat issues with assembly Avalonia.Controls:
+MembersMustExist : Member 'protected void Avalonia.Controls.Button.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.ButtonSpinner.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.CalendarDatePicker.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.ContextMenu.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
 TypesMustExist : Type 'Avalonia.Controls.DropDown' does not exist in the implementation but it does exist in the contract.
 TypesMustExist : Type 'Avalonia.Controls.DropDownItem' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.Expander.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.Boolean Avalonia.Controls.IMenuItem.StaysOpenOnClick' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.Boolean Avalonia.Controls.IMenuItem.StaysOpenOnClick.get()' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.IMenuItem.StaysOpenOnClick.set(System.Boolean)' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.INativeMenuExporterEventsImplBridge.RaiseClosed()' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.INativeMenuExporterEventsImplBridge.RaiseOpening()' is present in the implementation but not in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.ItemsRepeater.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.DirectProperty<Avalonia.Controls.NumericUpDown, System.Double> Avalonia.DirectProperty<Avalonia.Controls.NumericUpDown, System.Double> Avalonia.Controls.NumericUpDown.ValueProperty' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.StyledProperty<System.Double> Avalonia.StyledProperty<System.Double> Avalonia.Controls.NumericUpDown.IncrementProperty' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.StyledProperty<System.Double> Avalonia.StyledProperty<System.Double> Avalonia.Controls.NumericUpDown.MaximumProperty' does not exist in the implementation but it does exist in the contract.
@@ -30,7 +36,9 @@ MembersMustExist : Member 'public void Avalonia.Controls.NumericUpDown.Value.set
 MembersMustExist : Member 'public void Avalonia.Controls.NumericUpDownValueChangedEventArgs..ctor(Avalonia.Interactivity.RoutedEvent, System.Double, System.Double)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public System.Double Avalonia.Controls.NumericUpDownValueChangedEventArgs.NewValue.get()' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public System.Double Avalonia.Controls.NumericUpDownValueChangedEventArgs.OldValue.get()' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.ProgressBar.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.StyledProperty<System.Boolean> Avalonia.StyledProperty<System.Boolean> Avalonia.Controls.ScrollViewer.AllowAutoHideProperty' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.Slider.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.AttachedProperty<Avalonia.Media.FontFamily> Avalonia.AttachedProperty<Avalonia.Media.FontFamily> Avalonia.Controls.TextBlock.FontFamilyProperty' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.AttachedProperty<Avalonia.Media.FontStyle> Avalonia.AttachedProperty<Avalonia.Media.FontStyle> Avalonia.Controls.TextBlock.FontStyleProperty' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.AttachedProperty<Avalonia.Media.FontWeight> Avalonia.AttachedProperty<Avalonia.Media.FontWeight> Avalonia.Controls.TextBlock.FontWeightProperty' does not exist in the implementation but it does exist in the contract.
@@ -51,10 +59,12 @@ MembersMustExist : Member 'public void Avalonia.Controls.TextBlock.SetFontSize(A
 MembersMustExist : Member 'public void Avalonia.Controls.TextBlock.SetFontStyle(Avalonia.Controls.Control, Avalonia.Media.FontStyle)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Controls.TextBlock.SetFontWeight(Avalonia.Controls.Control, Avalonia.Media.FontWeight)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Controls.TextBlock.SetForeground(Avalonia.Controls.Control, Avalonia.Media.IBrush)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.TextBox.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
 CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Controls.TopLevel' does not implement interface 'Avalonia.Utilities.IWeakSubscriber<Avalonia.Controls.ResourcesChangedEventArgs>' in the implementation but it does in the contract.
 CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Controls.Viewbox' does not inherit from base type 'Avalonia.Controls.Decorator' in the implementation but it does in the contract.
 MembersMustExist : Member 'public Avalonia.AvaloniaProperty<Avalonia.Media.Stretch> Avalonia.AvaloniaProperty<Avalonia.Media.Stretch> Avalonia.Controls.Viewbox.StretchProperty' does not exist in the implementation but it does exist in the contract.
 CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Controls.Window' does not implement interface 'Avalonia.Utilities.IWeakSubscriber<Avalonia.Controls.ResourcesChangedEventArgs>' in the implementation but it does in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.Window.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
 CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Controls.WindowBase' does not implement interface 'Avalonia.Utilities.IWeakSubscriber<Avalonia.Controls.ResourcesChangedEventArgs>' in the implementation but it does in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.EventHandler<Avalonia.Controls.ApplicationLifetimes.ShutdownRequestedEventArgs> Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.ShutdownRequested' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.add_ShutdownRequested(System.EventHandler<Avalonia.Controls.ApplicationLifetimes.ShutdownRequestedEventArgs>)' is present in the implementation but not in the contract.
@@ -65,12 +75,17 @@ MembersMustExist : Member 'public System.Action<Avalonia.Size> Avalonia.Controls
 MembersMustExist : Member 'public void Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.Resized.set(System.Action<Avalonia.Size>)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.SetCursor(Avalonia.Platform.IPlatformHandle)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.AvaloniaProperty Avalonia.AvaloniaProperty Avalonia.Controls.Notifications.NotificationCard.CloseOnClickProperty' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.Notifications.WindowNotificationManager.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.Platform.ITopLevelNativeMenuExporter.SetNativeMenu(Avalonia.Controls.NativeMenu)' is present in the contract but not in the implementation.
+MembersMustExist : Member 'protected void Avalonia.Controls.Presenters.ScrollContentPresenter.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'protected Avalonia.Media.FormattedText Avalonia.Controls.Presenters.TextPresenter.CreateFormattedText()' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.Media.FormattedText Avalonia.Controls.Presenters.TextPresenter.FormattedText.get()' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public System.Int32 Avalonia.Controls.Presenters.TextPresenter.GetCaretIndex(Avalonia.Point)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'protected void Avalonia.Controls.Presenters.TextPresenter.InvalidateFormattedText()' does not exist in the implementation but it does exist in the contract.
 CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Controls.Primitives.PopupRoot' does not implement interface 'Avalonia.Utilities.IWeakSubscriber<Avalonia.Controls.ResourcesChangedEventArgs>' in the implementation but it does in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.Primitives.ScrollBar.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.Primitives.SelectingItemsControl.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'protected void Avalonia.Controls.Primitives.Track.OnPropertyChanged<T>(Avalonia.AvaloniaPropertyChangedEventArgs<T>)' does not exist in the implementation but it does exist in the contract.
 TypesMustExist : Type 'Avalonia.Platform.ExportWindowingSubsystemAttribute' does not exist in the implementation but it does exist in the contract.
 EnumValuesMustMatch : Enum value 'Avalonia.Platform.ExtendClientAreaChromeHints Avalonia.Platform.ExtendClientAreaChromeHints.Default' is (System.Int32)2 in the implementation but (System.Int32)1 in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.Screen Avalonia.Platform.IScreenImpl.ScreenFromPoint(Avalonia.PixelPoint)' is present in the implementation but not in the contract.
@@ -94,4 +109,4 @@ InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platfor
 MembersMustExist : Member 'public void Avalonia.Platform.IWindowImpl.Resize(Avalonia.Size)' does not exist in the implementation but it does exist in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.IWindowImpl.Resize(Avalonia.Size, Avalonia.Platform.PlatformResizeReason)' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.ITrayIconImpl Avalonia.Platform.IWindowingPlatform.CreateTrayIcon()' is present in the implementation but not in the contract.
-Total Issues: 95
+Total Issues: 110

src/Avalonia.Controls/AutoCompleteBox.cs

@@ -1346,12 +1346,16 @@ namespace Avalonia.Controls
         /// enabled.
         /// </summary>
         /// <param name="property">The property.</param>
-        /// <param name="value">The new binding value for the property.</param>
-        protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
+        /// <param name="state">The current data binding state.</param>
+        /// <param name="error">The current data binding error, if any.</param>
+        protected override void UpdateDataValidation(
+            AvaloniaProperty property,
+            BindingValueType state,
+            Exception? error)
         {
             if (property == TextProperty || property == SelectedItemProperty)
             {
-                DataValidationErrors.SetError(this, value.Error);
+                DataValidationErrors.SetError(this, error);
             }
         }
 

src/Avalonia.Controls/Button.cs

@@ -413,7 +413,7 @@ namespace Avalonia.Controls
         }
 
         /// <inheritdoc/>
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
@@ -421,12 +421,13 @@ namespace Avalonia.Controls
             {
                 if (((ILogical)this).IsAttachedToLogicalTree)
                 {
-                    if (change.OldValue.GetValueOrDefault() is ICommand oldCommand)
+                    var (oldValue, newValue) = change.GetOldAndNewValue<ICommand?>();
+                    if (oldValue is ICommand oldCommand)
                     {
                         oldCommand.CanExecuteChanged -= CanExecuteChanged;
                     }
 
-                    if (change.NewValue.GetValueOrDefault() is ICommand newCommand)
+                    if (newValue is ICommand newCommand)
                     {
                         newCommand.CanExecuteChanged += CanExecuteChanged;
                     }
@@ -440,7 +441,7 @@ namespace Avalonia.Controls
             }
             else if (change.Property == IsCancelProperty)
             {
-                var isCancel = change.NewValue.GetValueOrDefault<bool>();
+                var isCancel = change.GetNewValue<bool>();
 
                 if (VisualRoot is IInputElement inputRoot)
                 {
@@ -456,7 +457,7 @@ namespace Avalonia.Controls
             }
             else if (change.Property == IsDefaultProperty)
             {
-                var isDefault = change.NewValue.GetValueOrDefault<bool>();
+                var isDefault = change.GetNewValue<bool>();
 
                 if (VisualRoot is IInputElement inputRoot)
                 {
@@ -476,8 +477,7 @@ namespace Avalonia.Controls
             }
             else if (change.Property == FlyoutProperty)
             {
-                var oldFlyout = change.OldValue.GetValueOrDefault() as FlyoutBase;
-                var newFlyout = change.NewValue.GetValueOrDefault() as FlyoutBase;
+                var (oldFlyout, newFlyout) = change.GetOldAndNewValue<FlyoutBase?>();
 
                 // If flyout is changed while one is already open, make sure we 
                 // close the old one first
@@ -498,12 +498,15 @@ namespace Avalonia.Controls
         protected override AutomationPeer OnCreateAutomationPeer() => new ButtonAutomationPeer(this);
 
         /// <inheritdoc/>
-        protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
+        protected override void UpdateDataValidation(
+            AvaloniaProperty property,
+            BindingValueType state,
+            Exception? error)
         {
-            base.UpdateDataValidation(property, value);
+            base.UpdateDataValidation(property, state, error);
             if (property == CommandProperty)
             {
-                if (value.Type == BindingValueType.BindingError)
+                if (state == BindingValueType.BindingError)
                 {
                     if (_commandCanExecute)
                     {

src/Avalonia.Controls/ButtonSpinner.cs

@@ -210,13 +210,13 @@ namespace Avalonia.Controls
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == ButtonSpinnerLocationProperty)
             {
-                UpdatePseudoClasses(change.NewValue.GetValueOrDefault<Location>());
+                UpdatePseudoClasses(change.GetNewValue<Location>());
             }
         }
 

src/Avalonia.Controls/Calendar/CalendarDatePicker.cs

@@ -540,11 +540,11 @@ namespace Avalonia.Controls
             }
         }
 
-        protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
+        protected override void UpdateDataValidation(AvaloniaProperty property, BindingValueType state, Exception? error)
         {
             if (property == SelectedDateProperty)
             {
-                DataValidationErrors.SetError(this, value.Error);
+                DataValidationErrors.SetError(this, error);
             }
         }
 

src/Avalonia.Controls/ContextMenu.cs

@@ -241,13 +241,13 @@ namespace Avalonia.Controls
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == WindowManagerAddShadowHintProperty && _popup != null)
             {
-                _popup.WindowManagerAddShadowHint = change.NewValue.GetValueOrDefault<bool>();
+                _popup.WindowManagerAddShadowHint = change.GetNewValue<bool>();
             }
         }
 

src/Avalonia.Controls/Control.cs

@@ -348,7 +348,7 @@ namespace Avalonia.Controls
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 

src/Avalonia.Controls/Documents/Inline.cs

@@ -55,7 +55,7 @@ namespace Avalonia.Controls.Documents
                 TextDecorations, Foreground, Background, BaselineAlignment);
         }
         
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 

src/Avalonia.Controls/Documents/Run.cs

@@ -71,7 +71,7 @@ namespace Avalonia.Controls.Documents
             return text.Length;
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 

src/Avalonia.Controls/Documents/TextElement.cs

@@ -256,7 +256,7 @@ namespace Avalonia.Controls.Documents
         /// </summary>
         public event EventHandler? Invalidated;
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 

src/Avalonia.Controls/Expander.cs

@@ -106,13 +106,13 @@ namespace Avalonia.Controls
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == ExpandDirectionProperty)
             {
-                UpdatePseudoClasses(change.NewValue.GetValueOrDefault<ExpandDirection>());
+                UpdatePseudoClasses(change.GetNewValue<ExpandDirection>());
             }
         }
 

src/Avalonia.Controls/ItemsControl.cs

@@ -341,13 +341,13 @@ namespace Avalonia.Controls
             return new ItemsControlAutomationPeer(this);
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == ItemCountProperty)
             {
-                UpdatePseudoClasses(change.NewValue.GetValueOrDefault<int>());
+                UpdatePseudoClasses(change.GetNewValue<int>());
             }
         }
 

src/Avalonia.Controls/MaskedTextBox.cs

@@ -280,7 +280,7 @@ namespace Avalonia.Controls
             base.OnLostFocus(e);
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             void UpdateMaskProvider()
             {

src/Avalonia.Controls/MenuItem.cs

@@ -501,12 +501,15 @@ namespace Avalonia.Controls
             return new MenuItemAutomationPeer(this);
         }
 
-        protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
+        protected override void UpdateDataValidation(
+            AvaloniaProperty property,
+            BindingValueType state,
+            Exception? error)
         {
-            base.UpdateDataValidation(property, value);
+            base.UpdateDataValidation(property, state, error);
             if (property == CommandProperty)
             {
-                _commandBindingError = value.Type == BindingValueType.BindingError;
+                _commandBindingError = state == BindingValueType.BindingError;
                 if (_commandBindingError && _commandCanExecute)
                 {
                     _commandCanExecute = false;

src/Avalonia.Controls/Notifications/WindowNotificationManager.cs

@@ -139,13 +139,13 @@ namespace Avalonia.Controls.Notifications
             notificationControl.Close();
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == PositionProperty)
             {
-                UpdatePseudoClasses(change.NewValue.GetValueOrDefault<NotificationPosition>());
+                UpdatePseudoClasses(change.GetNewValue<NotificationPosition>());
             }
         }
 

src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs

@@ -403,12 +403,16 @@ namespace Avalonia.Controls
         /// enabled.
         /// </summary>
         /// <param name="property">The property.</param>
-        /// <param name="value">The new binding value for the property.</param>
-        protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
+        /// <param name="state">The current data binding state.</param>
+        /// <param name="error">The current data binding error, if any.</param>
+        protected override void UpdateDataValidation(
+            AvaloniaProperty property,
+            BindingValueType state,
+            Exception? error)
         {
             if (property == TextProperty || property == ValueProperty)
             {
-                DataValidationErrors.SetError(this, value.Error);
+                DataValidationErrors.SetError(this, error);
             }
         }
 

src/Avalonia.Controls/Presenters/ContentPresenter.cs

@@ -403,7 +403,7 @@ namespace Avalonia.Controls.Presenters
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
             switch (change.Property.Name)

src/Avalonia.Controls/Presenters/ScrollContentPresenter.cs

@@ -469,7 +469,7 @@ namespace Avalonia.Controls.Presenters
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             if (change.Property == OffsetProperty && !_arranging)
             {

src/Avalonia.Controls/Presenters/TextPresenter.cs

@@ -776,7 +776,7 @@ namespace Avalonia.Controls.Presenters
             _caretTimer.Tick -= CaretTimerTick;
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
             

src/Avalonia.Controls/Primitives/AdornerLayer.cs

@@ -69,15 +69,18 @@ namespace Avalonia.Controls.Primitives
         {
             foreach (var child in Children)
             {
-                var info = child.GetValue(s_adornedElementInfoProperty);
-
-                if (info != null && info.Bounds.HasValue)
-                {
-                    child.Measure(info.Bounds.Value.Bounds.Size);
-                }
-                else
+                if (child is AvaloniaObject ao)
                 {
-                    child.Measure(availableSize);
+                    var info = ao.GetValue(s_adornedElementInfoProperty);
+
+                    if (info != null && info.Bounds.HasValue)
+                    {
+                        child.Measure(info.Bounds.Value.Bounds.Size);
+                    }
+                    else
+                    {
+                        child.Measure(availableSize);
+                    }
                 }
             }
 
@@ -88,19 +91,22 @@ namespace Avalonia.Controls.Primitives
         {
             foreach (var child in Children)
             {
-                var info = child.GetValue(s_adornedElementInfoProperty);
-                var isClipEnabled = child.GetValue(IsClipEnabledProperty);
-
-                if (info != null && info.Bounds.HasValue)
-                {
-                    child.RenderTransform = new MatrixTransform(info.Bounds.Value.Transform);
-                    child.RenderTransformOrigin = new RelativePoint(new Point(0,0), RelativeUnit.Absolute);
-                    UpdateClip(child, info.Bounds.Value, isClipEnabled);
-                    child.Arrange(info.Bounds.Value.Bounds);
-                }
-                else
+                if (child is AvaloniaObject ao)
                 {
-                    child.Arrange(new Rect(finalSize));
+                    var info = ao.GetValue(s_adornedElementInfoProperty);
+                    var isClipEnabled = ao.GetValue(IsClipEnabledProperty);
+
+                    if (info != null && info.Bounds.HasValue)
+                    {
+                        child.RenderTransform = new MatrixTransform(info.Bounds.Value.Transform);
+                        child.RenderTransformOrigin = new RelativePoint(new Point(0, 0), RelativeUnit.Absolute);
+                        UpdateClip(child, info.Bounds.Value, isClipEnabled);
+                        child.Arrange(info.Bounds.Value.Bounds);
+                    }
+                    else
+                    {
+                        child.Arrange(new Rect(finalSize));
+                    }
                 }
             }
 

src/Avalonia.Controls/Primitives/ScrollBar.cs

@@ -194,13 +194,13 @@ namespace Avalonia.Controls.Primitives
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == OrientationProperty)
             {
-                UpdatePseudoClasses(change.NewValue.GetValueOrDefault<Orientation>());
+                UpdatePseudoClasses(change.GetNewValue<Orientation>());
             }
             else if (change.Property == AllowAutoHideProperty)
             {

src/Avalonia.Controls/Primitives/SelectingItemsControl.cs

@@ -501,12 +501,16 @@ namespace Avalonia.Controls.Primitives
         /// enabled.
         /// </summary>
         /// <param name="property">The property.</param>
-        /// <param name="value">The new binding value for the property.</param>
-        protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
+        /// <param name="state">The current data binding state.</param>
+        /// <param name="error">The current data binding error, if any.</param>
+        protected override void UpdateDataValidation(
+            AvaloniaProperty property,
+            BindingValueType state,
+            Exception? error)
         {
             if (property == SelectedItemProperty)
             {
-                DataValidationErrors.SetError(this, value.Error);
+                DataValidationErrors.SetError(this, error);
             }
         }
         
@@ -533,9 +537,9 @@ namespace Avalonia.Controls.Primitives
 
                 bool Match(ItemContainerInfo info)
                 {
-                    if (info.ContainerControl.IsSet(TextSearch.TextProperty))
+                    if (info.ContainerControl is AvaloniaObject ao && ao.IsSet(TextSearch.TextProperty))
                     {
-                        var searchText = info.ContainerControl.GetValue(TextSearch.TextProperty);
+                        var searchText = ao.GetValue(TextSearch.TextProperty);
 
                         if (searchText?.StartsWith(_textSearchTerm, StringComparison.OrdinalIgnoreCase) == true)
                         {
@@ -585,7 +589,7 @@ namespace Avalonia.Controls.Primitives
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
@@ -595,7 +599,7 @@ namespace Avalonia.Controls.Primitives
             }
             if (change.Property == ItemsProperty && _updateState is null && _selection is object)
             {
-                var newValue = change.NewValue.GetValueOrDefault<IEnumerable>();
+                var newValue = change.GetNewValue<IEnumerable>();
                 _selection.Source = newValue;
 
                 if (newValue is null)
@@ -605,7 +609,7 @@ namespace Avalonia.Controls.Primitives
             }
             else if (change.Property == SelectionModeProperty && _selection is object)
             {
-                var newValue = change.NewValue.GetValueOrDefault<SelectionMode>();
+                var newValue = change.GetNewValue<SelectionMode>();
                 _selection.SingleSelect = !newValue.HasAllFlags(SelectionMode.Multiple);
             }
             else if (change.Property == WrapSelectionProperty)

src/Avalonia.Controls/Primitives/Track.cs

@@ -291,13 +291,13 @@ namespace Avalonia.Controls.Primitives
             return arrangeSize;
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == OrientationProperty)
             {
-                UpdatePseudoClasses(change.NewValue.GetValueOrDefault<Orientation>());
+                UpdatePseudoClasses(change.GetNewValue<Orientation>());
             }
         }
 

src/Avalonia.Controls/ProgressBar.cs

@@ -178,17 +178,17 @@ namespace Avalonia.Controls
             return base.ArrangeOverride(finalSize);
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == IsIndeterminateProperty)
             {
-                UpdatePseudoClasses(change.NewValue.GetValueOrDefault<bool>(), null);
+                UpdatePseudoClasses(change.GetNewValue<bool>(), null);
             }
             else if (change.Property == OrientationProperty)
             {
-                UpdatePseudoClasses(null, change.NewValue.GetValueOrDefault<Orientation>());
+                UpdatePseudoClasses(null, change.GetNewValue<Orientation>());
             }
         }
 

src/Avalonia.Controls/RepeatButton.cs

@@ -70,11 +70,11 @@ namespace Avalonia.Controls
             _repeatTimer?.Stop();
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
-            if (change.Property == IsPressedProperty && change.NewValue.GetValueOrDefault<bool>() == false)
+            if (change.Property == IsPressedProperty && change.GetNewValue<bool>() == false)
             {
                 StopTimer();
             }

src/Avalonia.Controls/Repeater/ItemsRepeater.cs

@@ -20,7 +20,7 @@ namespace Avalonia.Controls
     /// Represents a data-driven collection control that incorporates a flexible layout system,
     /// custom views, and virtualization.
     /// </summary>
-    public class ItemsRepeater : Panel, IChildIndexProvider, IWeakEventSubscriber<EventArgs>
+    public class ItemsRepeater : Panel, IChildIndexProvider
     {
         /// <summary>
         /// Defines the <see cref="HorizontalCacheLength"/> property.
@@ -60,6 +60,7 @@ namespace Avalonia.Controls
 
         private readonly ViewManager _viewManager;
         private readonly ViewportManager _viewportManager;
+        private readonly TargetWeakEventSubscriber<ItemsRepeater, EventArgs> _layoutWeakSubscriber;
         private IEnumerable? _items;
         private VirtualizingLayoutContext? _layoutContext;
         private EventHandler<ChildIndexChangedEventArgs>? _childIndexChanged;
@@ -74,6 +75,15 @@ namespace Avalonia.Controls
         /// </summary>
         public ItemsRepeater()
         {
+            _layoutWeakSubscriber = new TargetWeakEventSubscriber<ItemsRepeater, EventArgs>(
+                this, static (target, _, ev, _) =>
+                {
+                    if (ev == AttachedLayout.ArrangeInvalidatedWeakEvent)
+                        target.InvalidateArrange();
+                    else if (ev == AttachedLayout.MeasureInvalidatedWeakEvent)
+                        target.InvalidateMeasure();
+                });
+
             _viewManager = new ViewManager(this);
             _viewportManager = new ViewportManager(this);
             KeyboardNavigation.SetTabNavigation(this, KeyboardNavigationMode.Once);
@@ -257,10 +267,9 @@ namespace Avalonia.Controls
 
         internal void UnpinElement(IControl element) => _viewManager.UpdatePin(element, false);
 
-        internal static VirtualizationInfo TryGetVirtualizationInfo(IControl element)
+        internal static VirtualizationInfo? TryGetVirtualizationInfo(IControl element)
         {
-            var value = element.GetValue(VirtualizationInfoProperty);
-            return value;
+            return (element as AvaloniaObject)?.GetValue(VirtualizationInfoProperty);
         }
 
         internal static VirtualizationInfo CreateAndInitializeVirtualizationInfo(IControl element)
@@ -277,15 +286,20 @@ namespace Avalonia.Controls
 
         internal static VirtualizationInfo GetVirtualizationInfo(IControl element)
         {
-            var result = element.GetValue(VirtualizationInfoProperty);
-
-            if (result == null)
+            if (element is AvaloniaObject ao)
             {
-                result = new VirtualizationInfo();
-                element.SetValue(VirtualizationInfoProperty, result);
+                var result = ao.GetValue(VirtualizationInfoProperty);
+
+                if (result == null)
+                {
+                    result = new VirtualizationInfo();
+                    ao.SetValue(VirtualizationInfoProperty, result);
+                }
+
+                return result;
             }
 
-            return result;
+            throw new NotSupportedException("Custom implementations of IAvaloniaObject not supported.");
         }
 
         private protected override void InvalidateMeasureOnChildrenChanged()
@@ -391,11 +405,7 @@ namespace Avalonia.Controls
                         var newBounds = element.Bounds;
                         virtInfo.ArrangeBounds = newBounds;
 
-                        if (!virtInfo.IsRegisteredAsAnchorCandidate)
-                        {
-                            _viewportManager.RegisterScrollAnchorCandidate(element);
-                            virtInfo.IsRegisteredAsAnchorCandidate = true;
-                        }
+                        _viewportManager.RegisterScrollAnchorCandidate(element, virtInfo);
                     }
                 }
 
@@ -420,12 +430,11 @@ namespace Avalonia.Controls
             _viewportManager.ResetScrollers();
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             if (change.Property == ItemsProperty)
             {
-                var oldEnumerable = change.OldValue.GetValueOrDefault<IEnumerable>();
-                var newEnumerable = change.NewValue.GetValueOrDefault<IEnumerable>();
+                var (oldEnumerable, newEnumerable) = change.GetOldAndNewValue<IEnumerable?>();
 
                 if (oldEnumerable != newEnumerable)
                 {
@@ -440,23 +449,21 @@ namespace Avalonia.Controls
             }
             else if (change.Property == ItemTemplateProperty)
             {
-                OnItemTemplateChanged(
-                    change.OldValue.GetValueOrDefault<IDataTemplate>(),
-                    change.NewValue.GetValueOrDefault<IDataTemplate>());
+                var (oldvalue, newValue) = change.GetOldAndNewValue<IDataTemplate?>();
+                OnItemTemplateChanged(oldvalue, newValue);
             }
             else if (change.Property == LayoutProperty)
             {
-                OnLayoutChanged(
-                    change.OldValue.GetValueOrDefault<AttachedLayout>(),
-                    change.NewValue.GetValueOrDefault<AttachedLayout>());
+                var (oldvalue, newValue) = change.GetOldAndNewValue<AttachedLayout>();
+                OnLayoutChanged(oldvalue, newValue);
             }
             else if (change.Property == HorizontalCacheLengthProperty)
             {
-                _viewportManager.HorizontalCacheLength = change.NewValue.GetValueOrDefault<double>();
+                _viewportManager.HorizontalCacheLength = change.GetNewValue<double>();
             }
             else if (change.Property == VerticalCacheLengthProperty)
             {
-                _viewportManager.VerticalCacheLength = change.NewValue.GetValueOrDefault<double>();
+                _viewportManager.VerticalCacheLength = change.GetNewValue<double>();
             }
 
             base.OnPropertyChanged(change);
@@ -480,7 +487,7 @@ namespace Avalonia.Controls
                     _processingItemsSourceChange.Action == NotifyCollectionChangedAction.Reset);
 
             _viewManager.ClearElement(element, isClearedDueToCollectionChange);
-            _viewportManager.OnElementCleared(element);
+            _viewportManager.OnElementCleared(element, GetVirtualizationInfo(element));
         }
 
         private int GetElementIndexImpl(IControl element)
@@ -491,7 +498,7 @@ namespace Avalonia.Controls
             if (parent == this)
             {
                 var virtInfo = TryGetVirtualizationInfo(element);
-                return _viewManager.GetElementIndex(virtInfo);
+                return _viewManager.GetElementIndex(virtInfo!);
             }
 
             return -1;
@@ -728,8 +735,8 @@ namespace Avalonia.Controls
             {
                 oldValue.UninitializeForContext(LayoutContext);
 
-                AttachedLayout.MeasureInvalidatedWeakEvent.Unsubscribe(oldValue, this);
-                AttachedLayout.ArrangeInvalidatedWeakEvent.Unsubscribe(oldValue, this);
+                AttachedLayout.MeasureInvalidatedWeakEvent.Unsubscribe(oldValue, _layoutWeakSubscriber);
+                AttachedLayout.ArrangeInvalidatedWeakEvent.Unsubscribe(oldValue, _layoutWeakSubscriber);
 
                 // Walk through all the elements and make sure they are cleared
                 foreach (var element in Children)
@@ -747,8 +754,8 @@ namespace Avalonia.Controls
             {
                 newValue.InitializeForContext(LayoutContext);
 
-                AttachedLayout.MeasureInvalidatedWeakEvent.Subscribe(newValue, this);
-                AttachedLayout.ArrangeInvalidatedWeakEvent.Subscribe(newValue, this);
+                AttachedLayout.MeasureInvalidatedWeakEvent.Subscribe(newValue, _layoutWeakSubscriber);
+                AttachedLayout.ArrangeInvalidatedWeakEvent.Subscribe(newValue, _layoutWeakSubscriber);
             }
 
             bool isVirtualizingLayout = newValue != null && newValue is VirtualizingLayout;
@@ -798,15 +805,7 @@ namespace Avalonia.Controls
         {
             _viewportManager.OnBringIntoViewRequested(e);
         }
-
-        void IWeakEventSubscriber<EventArgs>.OnEvent(object? sender, WeakEvent ev, EventArgs e)
-        {
-            if(ev == AttachedLayout.ArrangeInvalidatedWeakEvent)
-                InvalidateArrange();
-            else if (ev == AttachedLayout.MeasureInvalidatedWeakEvent)
-                InvalidateMeasure();
-        }
-
+        
         private VirtualizingLayoutContext GetLayoutContext()
         {
             if (_layoutContext == null)

src/Avalonia.Controls/Repeater/RecyclePool.cs

@@ -80,8 +80,8 @@ namespace Avalonia.Controls
             return null;
         }
 
-        internal string GetReuseKey(IControl element) => element.GetValue(ReuseKeyProperty);
-        internal void SetReuseKey(IControl element, string value) => element.SetValue(ReuseKeyProperty, value);
+        internal string GetReuseKey(IControl element) => ((Control)element).GetValue(ReuseKeyProperty);
+        internal void SetReuseKey(IControl element, string value) => ((Control)element).SetValue(ReuseKeyProperty, value);
 
         private IPanel? EnsureOwnerIsPanelOrNull(IControl? owner)
         {

src/Avalonia.Controls/Repeater/ViewManager.cs

@@ -47,7 +47,7 @@ namespace Avalonia.Controls
                 if (madeAnchor != null)
                 {
                     var anchorVirtInfo = ItemsRepeater.TryGetVirtualizationInfo(madeAnchor);
-                    if (anchorVirtInfo.Index == index)
+                    if (anchorVirtInfo!.Index == index)
                     {
                         element = madeAnchor;
                     }
@@ -60,12 +60,12 @@ namespace Avalonia.Controls
             var virtInfo = ItemsRepeater.TryGetVirtualizationInfo(element);
             if (suppressAutoRecycle)
             {
-                virtInfo.AutoRecycleCandidate = false;
+                virtInfo!.AutoRecycleCandidate = false;
                 Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "GetElement: {Index} Not AutoRecycleCandidate:", virtInfo.Index);
             }
             else
             {
-                virtInfo.AutoRecycleCandidate = true;
+                virtInfo!.AutoRecycleCandidate = true;
                 virtInfo.KeepAlive = true;
                 Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "GetElement: {Index} AutoRecycleCandidate:", virtInfo.Index);
             }

src/Avalonia.Controls/Repeater/ViewportManager.cs

@@ -249,9 +249,10 @@ namespace Avalonia.Controls
             virtInfo.IsRegisteredAsAnchorCandidate = false;
         }
 
-        public void OnElementCleared(IControl element)
+        public void OnElementCleared(IControl element, VirtualizationInfo virtInfo)
         {
             _scroller?.UnregisterAnchorCandidate(element);
+            virtInfo.IsRegisteredAsAnchorCandidate = false;
         }
 
         public void OnOwnerMeasuring()
@@ -358,9 +359,12 @@ namespace Avalonia.Controls
                 {
                     foreach (var child in _owner.Children)
                     {
-                        if (child != targetChild)
+                        var info = ItemsRepeater.GetVirtualizationInfo(child);
+
+                        if (child != targetChild && info.IsRegisteredAsAnchorCandidate)
                         {
                             _scroller.UnregisterAnchorCandidate(child);
+                            info.IsRegisteredAsAnchorCandidate = false;
                         }
                     }
                 }
@@ -377,9 +381,13 @@ namespace Avalonia.Controls
             }
         }
 
-        public void RegisterScrollAnchorCandidate(IControl element)
+        public void RegisterScrollAnchorCandidate(IControl element, VirtualizationInfo virtInfo)
         {
-            _scroller?.RegisterAnchorCandidate(element);
+            if (!virtInfo.IsRegisteredAsAnchorCandidate)
+            {
+                _scroller?.RegisterAnchorCandidate(element);
+                virtInfo.IsRegisteredAsAnchorCandidate = true;
+            }
         }
 
         private IControl? GetImmediateChildOfRepeater(IControl descendant)
@@ -405,15 +413,18 @@ namespace Avalonia.Controls
             _isBringIntoViewInProgress = false;
             _makeAnchorElement = null;
 
+            // Undo the anchor deregistrations done by OnBringIntoViewRequested.
             if (_scroller is object)
             {
                 foreach (var child in _owner.Children)
                 {
                     var info = ItemsRepeater.GetVirtualizationInfo(child);
 
-                    if (info.IsRealized && info.IsHeldByLayout)
+                    // The item brought into view is still registered - don't register it more than once.
+                    if (info.IsRealized && info.IsHeldByLayout && !info.IsRegisteredAsAnchorCandidate)
                     {
                         _scroller.RegisterAnchorCandidate(child);
+                        info.IsRegisteredAsAnchorCandidate = true;
                     }
                 }
             }
@@ -430,7 +441,13 @@ namespace Avalonia.Controls
             {
                 foreach (var child in _owner.Children)
                 {
-                    _scroller.UnregisterAnchorCandidate(child);
+                    var info = ItemsRepeater.GetVirtualizationInfo(child);
+
+                    if (info.IsRegisteredAsAnchorCandidate)
+                    {
+                        _scroller.UnregisterAnchorCandidate(child);
+                        info.IsRegisteredAsAnchorCandidate = false;
+                    }
                 }
 
                 _scroller = null;

src/Avalonia.Controls/Slider.cs

@@ -361,21 +361,24 @@ namespace Avalonia.Controls
             Value = IsSnapToTickEnabled ? SnapToTick(finalValue) : finalValue;
         }
 
-        protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
+        protected override void UpdateDataValidation(
+            AvaloniaProperty property,
+            BindingValueType state,
+            Exception? error)
         {
             if (property == ValueProperty)
             {
-                DataValidationErrors.SetError(this, value.Error);
+                DataValidationErrors.SetError(this, error);
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == OrientationProperty)
             {
-                UpdatePseudoClasses(change.NewValue.GetValueOrDefault<Orientation>());
+                UpdatePseudoClasses(change.GetNewValue<Orientation>());
             }
         }
 

src/Avalonia.Controls/SplitButton/SplitButton.cs

@@ -276,19 +276,21 @@ namespace Avalonia.Controls
         }
 
         /// <inheritdoc/>
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> e)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs e)
         {
             if (e.Property == CommandProperty)
             {
                 if (_isAttachedToLogicalTree)
                 {
                     // Must unregister events here while a reference to the old command still exists
-                    if (e.OldValue.GetValueOrDefault() is ICommand oldCommand)
+                    var (oldValue, newValue) = e.GetOldAndNewValue<ICommand?>();
+
+                    if (oldValue is ICommand oldCommand)
                     {
                         oldCommand.CanExecuteChanged -= CanExecuteChanged;
                     }
 
-                    if (e.NewValue.GetValueOrDefault() is ICommand newCommand)
+                    if (newValue is ICommand newCommand)
                     {
                         newCommand.CanExecuteChanged += CanExecuteChanged;
                     }
@@ -302,8 +304,7 @@ namespace Avalonia.Controls
             }
             else if (e.Property == FlyoutProperty)
             {
-                var oldFlyout = e.OldValue.GetValueOrDefault() as FlyoutBase;
-                var newFlyout = e.NewValue.GetValueOrDefault() as FlyoutBase;
+                var (oldFlyout, newFlyout) = e.GetOldAndNewValue<FlyoutBase?>();
 
                 // If flyout is changed while one is already open, make sure we 
                 // close the old one first

src/Avalonia.Controls/SplitButton/ToggleSplitButton.cs

@@ -90,7 +90,7 @@ namespace Avalonia.Controls
         ////////////////////////////////////////////////////////////////////////
 
         /// <inheritdoc/>
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> e)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs e)
         {
             if (e.Property == IsCheckedProperty)
             {

src/Avalonia.Controls/TextBlock.cs

@@ -639,7 +639,7 @@ namespace Avalonia.Controls
 
         private static bool IsValidLineHeight(double lineHeight) => double.IsNaN(lineHeight) || lineHeight > 0;
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 

src/Avalonia.Controls/TextBox.cs

@@ -585,7 +585,7 @@ namespace Avalonia.Controls
             _imClient.SetPresenter(null, null);
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
@@ -594,7 +594,7 @@ namespace Avalonia.Controls
                 UpdatePseudoclasses();
                 UpdateCommandStates();
             }
-            else if (change.Property == IsUndoEnabledProperty && change.NewValue.GetValueOrDefault<bool>() == false)
+            else if (change.Property == IsUndoEnabledProperty && change.GetNewValue<bool>() == false)
             {
                 // from docs at
                 // https://docs.microsoft.com/en-us/dotnet/api/system.windows.controls.primitives.textboxbase.isundoenabled:
@@ -1262,11 +1262,14 @@ namespace Avalonia.Controls
             return new TextBoxAutomationPeer(this);
         }
 
-        protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
+        protected override void UpdateDataValidation(
+            AvaloniaProperty property,
+            BindingValueType state,
+            Exception? error)
         {
             if (property == TextProperty)
             {
-                DataValidationErrors.SetError(this, value.Error);
+                DataValidationErrors.SetError(this, error);
             }
         }
 

src/Avalonia.Controls/TopLevel.cs

@@ -34,8 +34,7 @@ namespace Avalonia.Controls
         ICloseable,
         IStyleHost,
         ILogicalRoot,
-        ITextInputMethodRoot,
-        IWeakEventSubscriber<ResourcesChangedEventArgs>
+        ITextInputMethodRoot
     {
         /// <summary>
         /// Defines the <see cref="ClientSize"/> property.
@@ -93,6 +92,7 @@ namespace Avalonia.Controls
         private WindowTransparencyLevel _actualTransparencyLevel;
         private ILayoutManager? _layoutManager;
         private Border? _transparencyFallbackBorder;
+        private TargetWeakEventSubscriber<TopLevel, ResourcesChangedEventArgs>? _resourcesChangesSubscriber;
 
         /// <summary>
         /// Initializes static members of the <see cref="TopLevel"/> class.
@@ -192,7 +192,13 @@ namespace Avalonia.Controls
 
             if (((IStyleHost)this).StylingParent is IResourceHost applicationResources)
             {
-                ResourcesChangedWeakEvent.Subscribe(applicationResources, this);
+                _resourcesChangesSubscriber = new TargetWeakEventSubscriber<TopLevel, ResourcesChangedEventArgs>(
+                    this, static (target, _, _, e) =>
+                    {
+                        ((ILogical)target).NotifyResourcesChanged(e);
+                    });
+
+                ResourcesChangedWeakEvent.Subscribe(applicationResources, _resourcesChangesSubscriber);
             }
 
             impl.LostFocus += PlatformImpl_LostFocus;
@@ -297,11 +303,6 @@ namespace Avalonia.Controls
         /// <inheritdoc/>
         IMouseDevice? IInputRoot.MouseDevice => PlatformImpl?.MouseDevice;
 
-        void IWeakEventSubscriber<ResourcesChangedEventArgs>.OnEvent(object? sender, WeakEvent ev, ResourcesChangedEventArgs e)
-        {
-            ((ILogical)this).NotifyResourcesChanged(e);
-        }
-
         /// <summary>
         /// Gets or sets a value indicating whether access keys are shown in the window.
         /// </summary>

src/Avalonia.Controls/TransitioningContentControl.cs

@@ -61,7 +61,7 @@ public class TransitioningContentControl : ContentControl
         _lastTransitionCts?.Cancel();
     }
 
-    protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+    protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
     {
         base.OnPropertyChanged(change);
 

src/Avalonia.Controls/TrayIcon.cs

@@ -206,7 +206,7 @@ namespace Avalonia.Controls
             }
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
@@ -216,15 +216,15 @@ namespace Avalonia.Controls
             }
             else if (change.Property == IsVisibleProperty)
             {
-                _impl?.SetIsVisible(change.NewValue.GetValueOrDefault<bool>());
+                _impl?.SetIsVisible(change.GetNewValue<bool>());
             }
             else if (change.Property == ToolTipTextProperty)
             {
-                _impl?.SetToolTipText(change.NewValue.GetValueOrDefault<string?>());
+                _impl?.SetToolTipText(change.GetNewValue<string?>());
             }
             else if (change.Property == MenuProperty)
             {
-                _impl?.MenuExporter?.SetNativeMenu(change.NewValue.GetValueOrDefault<NativeMenu>());
+                _impl?.MenuExporter?.SetNativeMenu(change.GetNewValue<NativeMenu?>());
             }
         }
 

src/Avalonia.Controls/TreeView.cs

@@ -401,7 +401,7 @@ namespace Avalonia.Controls
         protected virtual ITreeItemContainerGenerator CreateTreeItemContainerGenerator() =>
             CreateTreeItemContainerGenerator<TreeViewItem>();
 
-        protected virtual ITreeItemContainerGenerator CreateTreeItemContainerGenerator<TVItem>() where TVItem: TreeViewItem, new()
+        protected ITreeItemContainerGenerator CreateTreeItemContainerGenerator<TVItem>() where TVItem: TreeViewItem, new()
         {
             return new TreeItemContainerGenerator<TVItem>(
                 this,

src/Avalonia.Controls/TreeViewItem.cs

@@ -96,7 +96,7 @@ namespace Avalonia.Controls
         protected override IItemContainerGenerator CreateItemContainerGenerator() => CreateTreeItemContainerGenerator<TreeViewItem>();
 
         /// <inheritdoc/>
-        protected virtual ITreeItemContainerGenerator CreateTreeItemContainerGenerator<TVItem>()
+        protected ITreeItemContainerGenerator CreateTreeItemContainerGenerator<TVItem>()
             where TVItem: TreeViewItem, new()
         {
             return new TreeItemContainerGenerator<TVItem>(

src/Avalonia.Controls/Viewbox.cs

@@ -82,13 +82,13 @@ namespace Avalonia.Controls
             set => _containerVisual.RenderTransform = value;
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
             if (change.Property == ChildProperty)
             {
-                _containerVisual.Child = change.NewValue.GetValueOrDefault<IControl>();
+                _containerVisual.Child = change.GetNewValue<IControl>();
                 InvalidateMeasure();
             }
         }

src/Avalonia.Controls/Window.cs

@@ -1019,16 +1019,16 @@ namespace Avalonia.Controls
         /// </remarks>
         protected virtual void OnClosing(CancelEventArgs e) => Closing?.Invoke(this, e);
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
             if (change.Property == SystemDecorationsProperty)
             {
-                var typedNewValue = change.NewValue.GetValueOrDefault<SystemDecorations>();
+                var (typedOldValue, typedNewValue) = change.GetOldAndNewValue<SystemDecorations>();
 
                 PlatformImpl?.SetSystemDecorations(typedNewValue);
 
-                var o = change.OldValue.GetValueOrDefault<SystemDecorations>() == SystemDecorations.Full;
+                var o = typedOldValue == SystemDecorations.Full;
                 var n = typedNewValue == SystemDecorations.Full;
 
                 if (o != n)

src/Avalonia.Diagnostics/Diagnostics/Controls/ThicknessEditor.cs

@@ -92,7 +92,7 @@ namespace Avalonia.Diagnostics.Controls
             set => SetValue(HighlightProperty, value);
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
 
@@ -102,7 +102,7 @@ namespace Avalonia.Diagnostics.Controls
                 {
                     _isUpdatingThickness = true;
 
-                    var value = change.NewValue.GetValueOrDefault<Thickness>();
+                    var value = change.GetNewValue<Thickness>();
 
                     Left = value.Left;
                     Top = value.Top;

src/Avalonia.Diagnostics/Diagnostics/ViewModels/ControlLayoutViewModel.cs

@@ -110,7 +110,7 @@ namespace Avalonia.Diagnostics.ViewModels
 
         private void UpdateSizeConstraints()
         {
-            if (_control is IAvaloniaObject ao)
+            if (_control is AvaloniaObject ao)
             {
                 string? CreateConstraintInfo(StyledProperty<double> minProperty, StyledProperty<double> maxProperty)
                 {
@@ -191,7 +191,7 @@ namespace Avalonia.Diagnostics.ViewModels
                 }
                 else
                 {
-                    if (_control is IAvaloniaObject ao)
+                    if (_control is AvaloniaObject ao)
                     {
                         if (e.Property == Layoutable.MarginProperty)
                         {

src/Avalonia.Themes.Default/SimpleTheme.cs

@@ -116,7 +116,7 @@ namespace Avalonia.Themes.Default
             return false;
         }
 
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
             if (change.Property == ModeProperty)

src/Avalonia.Themes.Fluent/FluentTheme.cs

@@ -78,7 +78,7 @@ namespace Avalonia.Themes.Fluent
             set => SetValue(DensityStyleProperty, value);
         }
         
-        protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);
             if (change.Property == ModeProperty)

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs

@@ -138,7 +138,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             NameScopeSetNameScope = NameScope.GetMethod(new FindMethodMethodSignature("SetNameScope",
                 XamlIlTypes.Void, StyledElement, INameScope)
             { IsStatic = true });
-            AvaloniaObjectSetValueMethod = AvaloniaObject.FindMethod("SetValue", XamlIlTypes.Void,
+            AvaloniaObjectSetValueMethod = AvaloniaObject.FindMethod("SetValue", IDisposable,
                 false, AvaloniaProperty, XamlIlTypes.Object, BindingPriority);
             IPropertyInfo = cfg.TypeSystem.GetType("Avalonia.Data.Core.IPropertyInfo");
             ClrPropertyInfo = cfg.TypeSystem.GetType("Avalonia.Data.Core.ClrPropertyInfo");

src/Windows/Avalonia.Win32/WinRT/NativeWinRTMethods.cs

@@ -23,7 +23,7 @@ namespace Avalonia.Win32.WinRT
 
         [DllImport("api-ms-win-core-winrt-string-l1-1-0.dll", 
             CallingConvention = CallingConvention.StdCall, PreserveSig = false)]
-        internal static extern unsafe IntPtr WindowsDeleteString(IntPtr hString);
+        internal static extern unsafe void WindowsDeleteString(IntPtr hString);
         
         [DllImport("Windows.UI.Composition", EntryPoint = "DllGetActivationFactory",
             CallingConvention = CallingConvention.StdCall, PreserveSig = false)]

tests/Avalonia.Base.UnitTests/AvaloniaObjectTests_DataValidation.cs

@@ -52,14 +52,14 @@ namespace Avalonia.Base.UnitTests
             source.OnNext(BindingValue<int>.DataValidationError(new Exception()));
             source.OnNext(7);
 
-            var result = target.Notifications.Cast<BindingValue<int>>().ToList();
+            var result = target.Notifications;
             Assert.Equal(4, result.Count);
-            Assert.Equal(BindingValueType.Value, result[0].Type);
-            Assert.Equal(6, result[0].Value);
-            Assert.Equal(BindingValueType.BindingError, result[1].Type);
-            Assert.Equal(BindingValueType.DataValidationError, result[2].Type);
-            Assert.Equal(BindingValueType.Value, result[3].Type);
-            Assert.Equal(7, result[3].Value);
+            Assert.Equal(BindingValueType.Value, result[0].type);
+            Assert.Equal(6, result[0].value);
+            Assert.Equal(BindingValueType.BindingError, result[1].type);
+            Assert.Equal(BindingValueType.DataValidationError, result[2].type);
+            Assert.Equal(BindingValueType.Value, result[3].type);
+            Assert.Equal(7, result[3].value);
         }
 
         [Fact]
@@ -72,8 +72,7 @@ namespace Avalonia.Base.UnitTests
             target.Bind(Class1.NonValidatedDirectProperty, source);
             source.OnNext(1);
 
-            var result = target.Notifications.Cast<BindingValue<int>>().ToList();
-            Assert.Equal(1, result.Count);
+            Assert.Equal(1, target.Notifications.Count);
         }
 
         [Fact]
@@ -154,13 +153,14 @@ namespace Avalonia.Base.UnitTests
                 set { SetAndRaise(ValidatedDirectStringProperty, ref _directString, value); }
             }
 
-            public IList<object> Notifications { get; } = new List<object>();
+            public List<(BindingValueType type, object value)> Notifications { get; } = new();
 
-            protected override void UpdateDataValidation<T>(
-                AvaloniaProperty<T> property,
-                BindingValue<T> value)
+            protected override void UpdateDataValidation(
+                AvaloniaProperty property,
+                BindingValueType state,
+                Exception error)
             {
-                Notifications.Add(value);
+                Notifications.Add((state, GetValue(property)));
             }
         }
 

tests/Avalonia.Base.UnitTests/AvaloniaObjectTests_OnPropertyChanged.cs

@@ -109,25 +109,26 @@ namespace Avalonia.Base.UnitTests
             public List<AvaloniaPropertyChangedEventArgs> Changes { get; }
             public List<AvaloniaPropertyChangedEventArgs> CoreChanges { get; }
 
-            protected override void OnPropertyChangedCore<T>(AvaloniaPropertyChangedEventArgs<T> change)
+            protected override void OnPropertyChangedCore(AvaloniaPropertyChangedEventArgs change)
             {
                 CoreChanges.Add(Clone(change));
                 base.OnPropertyChangedCore(change);
             }
 
-            protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+            protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
             {
                 Changes.Add(Clone(change));
                 base.OnPropertyChanged(change);
             }
 
-            private static AvaloniaPropertyChangedEventArgs<T> Clone<T>(AvaloniaPropertyChangedEventArgs<T> change)
+            private static AvaloniaPropertyChangedEventArgs Clone(AvaloniaPropertyChangedEventArgs change)
             {
-                var result = new AvaloniaPropertyChangedEventArgs<T>(
+                var e = (AvaloniaPropertyChangedEventArgs<string>)change;
+                var result = new AvaloniaPropertyChangedEventArgs<string>(
                     change.Sender,
-                    change.Property,
-                    change.OldValue,
-                    change.NewValue,
+                    e.Property,
+                    e.OldValue,
+                    e.NewValue,
                     change.Priority);
 
                 if (!change.IsEffectiveValueChange)

tests/Avalonia.Base.UnitTests/AvaloniaPropertyTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using Avalonia.Data;
+using Avalonia.Styling;
 using Avalonia.Utilities;
 using Xunit;
 
@@ -146,46 +147,46 @@ namespace Avalonia.Base.UnitTests
                 OverrideMetadata(typeof(T), metadata);
             }
 
-            public override void Accept<TData>(IAvaloniaPropertyVisitor<TData> vistor, ref TData data)
-            {
-                throw new NotImplementedException();
-            }
-
             internal override IDisposable RouteBind(
-                IAvaloniaObject o,
+                AvaloniaObject o,
                 IObservable<BindingValue<object>> source,
                 BindingPriority priority)
             {
                 throw new NotImplementedException();
             }
 
-            internal override void RouteClearValue(IAvaloniaObject o)
+            internal override void RouteClearValue(AvaloniaObject o)
             {
                 throw new NotImplementedException();
             }
 
-            internal override object RouteGetValue(IAvaloniaObject o)
+            internal override object RouteGetValue(AvaloniaObject o)
             {
                 throw new NotImplementedException();
             }
 
-            internal override object RouteGetBaseValue(IAvaloniaObject o, BindingPriority maxPriority)
+            internal override object RouteGetBaseValue(AvaloniaObject o, BindingPriority maxPriority)
             {
                 throw new NotImplementedException();
             }
 
-            internal override void RouteInheritanceParentChanged(AvaloniaObject o, IAvaloniaObject oldParent)
+            internal override void RouteInheritanceParentChanged(AvaloniaObject o, AvaloniaObject oldParent)
             {
                 throw new NotImplementedException();
             }
 
             internal override IDisposable RouteSetValue(
-                IAvaloniaObject o,
+                AvaloniaObject o,
                 object value,
                 BindingPriority priority)
             {
                 throw new NotImplementedException();
             }
+
+            internal override ISetterInstance CreateSetterInstance(IStyleable target, object value)
+            {
+                throw new NotImplementedException();
+            }
         }
 
         private class Class1 : AvaloniaObject

tests/Avalonia.Base.UnitTests/PriorityValueTests.cs

@@ -10,8 +10,8 @@ namespace Avalonia.Base.UnitTests
 {
     public class PriorityValueTests
     {
-        private static readonly IValueSink NullSink = new MockSink();
-        private static readonly IAvaloniaObject Owner = Mock.Of<IAvaloniaObject>();
+        private static readonly AvaloniaObject Owner = new AvaloniaObject();
+        private static readonly ValueStore ValueStore = new ValueStore(Owner);
         private static readonly StyledProperty<string> TestProperty = new StyledProperty<string>(
             "Test",
             typeof(PriorityValueTests),
@@ -23,12 +23,12 @@ namespace Avalonia.Base.UnitTests
             var target = new PriorityValue<string>(
                 Owner,
                 TestProperty,
-                NullSink,
+                ValueStore,
                 new ConstantValueEntry<string>(
                     TestProperty,
                     "1",
                     BindingPriority.StyleTrigger,
-                    NullSink));
+                    new(ValueStore)));
 
             Assert.Equal("1", target.GetValue().Value);
             Assert.Equal(BindingPriority.StyleTrigger, target.Priority);
@@ -40,7 +40,7 @@ namespace Avalonia.Base.UnitTests
             var target = new PriorityValue<string>(
                 Owner,
                 TestProperty,
-                NullSink);
+                ValueStore);
 
             target.SetValue("animation", BindingPriority.Animation);
             target.SetValue("local", BindingPriority.LocalValue);
@@ -60,7 +60,7 @@ namespace Avalonia.Base.UnitTests
             var target = new PriorityValue<string>(
                 Owner,
                 TestProperty,
-                NullSink);
+                ValueStore);
 
             target.SetValue("1", BindingPriority.LocalValue);
             target.SetValue("2", BindingPriority.LocalValue);
@@ -74,7 +74,7 @@ namespace Avalonia.Base.UnitTests
             var target = new PriorityValue<string>(
                 Owner,
                 TestProperty,
-                NullSink);
+                ValueStore);
 
             target.SetValue("1", BindingPriority.Style);
             target.SetValue("2", BindingPriority.Animation);
@@ -93,7 +93,7 @@ namespace Avalonia.Base.UnitTests
             var target = new PriorityValue<string>(
                 Owner,
                 TestProperty,
-                NullSink);
+                ValueStore);
 
             Assert.Equal(BindingPriority.Unset, target.Priority);
             target.SetValue("style", BindingPriority.Style);
@@ -109,7 +109,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void Binding_With_Same_Priority_Should_Be_Appended()
         {
-            var target = new PriorityValue<string>(Owner, TestProperty, NullSink);
+            var target = new PriorityValue<string>(Owner, TestProperty, ValueStore);
             var source1 = new Source("1");
             var source2 = new Source("2");
 
@@ -129,7 +129,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void Binding_With_Higher_Priority_Should_Be_Appended()
         {
-            var target = new PriorityValue<string>(Owner, TestProperty, NullSink);
+            var target = new PriorityValue<string>(Owner, TestProperty, ValueStore);
             var source1 = new Source("1");
             var source2 = new Source("2");
 
@@ -149,7 +149,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void Binding_With_Lower_Priority_Should_Be_Prepended()
         {
-            var target = new PriorityValue<string>(Owner, TestProperty, NullSink);
+            var target = new PriorityValue<string>(Owner, TestProperty, ValueStore);
             var source1 = new Source("1");
             var source2 = new Source("2");
 
@@ -169,7 +169,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void Second_Binding_With_Lower_Priority_Should_Be_Inserted_In_Middle()
         {
-            var target = new PriorityValue<string>(Owner, TestProperty, NullSink);
+            var target = new PriorityValue<string>(Owner, TestProperty, ValueStore);
             var source1 = new Source("1");
             var source2 = new Source("2");
             var source3 = new Source("3");
@@ -191,7 +191,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void Competed_Binding_Should_Be_Removed()
         {
-            var target = new PriorityValue<string>(Owner, TestProperty, NullSink);
+            var target = new PriorityValue<string>(Owner, TestProperty, ValueStore);
             var source1 = new Source("1");
             var source2 = new Source("2");
             var source3 = new Source("3");
@@ -214,7 +214,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void Value_Should_Come_From_Last_Entry()
         {
-            var target = new PriorityValue<string>(Owner, TestProperty, NullSink);
+            var target = new PriorityValue<string>(Owner, TestProperty, ValueStore);
             var source1 = new Source("1");
             var source2 = new Source("2");
             var source3 = new Source("3");
@@ -229,7 +229,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void LocalValue_Should_Override_LocalValue_Binding()
         {
-            var target = new PriorityValue<string>(Owner, TestProperty, NullSink);
+            var target = new PriorityValue<string>(Owner, TestProperty, ValueStore);
             var source1 = new Source("1");
 
             target.AddBinding(source1, BindingPriority.LocalValue).Start();
@@ -241,7 +241,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void LocalValue_Should_Override_Style_Binding()
         {
-            var target = new PriorityValue<string>(Owner, TestProperty, NullSink);
+            var target = new PriorityValue<string>(Owner, TestProperty, ValueStore);
             var source1 = new Source("1");
 
             target.AddBinding(source1, BindingPriority.Style).Start();
@@ -253,7 +253,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void LocalValue_Should_Not_Override_Animation_Binding()
         {
-            var target = new PriorityValue<string>(Owner, TestProperty, NullSink);
+            var target = new PriorityValue<string>(Owner, TestProperty, ValueStore);
             var source1 = new Source("1");
 
             target.AddBinding(source1, BindingPriority.Animation).Start();
@@ -265,7 +265,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void NonAnimated_Value_Should_Be_Correct_1()
         {
-            var target = new PriorityValue<string>(Owner, TestProperty, NullSink);
+            var target = new PriorityValue<string>(Owner, TestProperty, ValueStore);
             var source1 = new Source("1");
             var source2 = new Source("2");
             var source3 = new Source("3");
@@ -281,7 +281,7 @@ namespace Avalonia.Base.UnitTests
         [Fact]
         public void NonAnimated_Value_Should_Be_Correct_2()
         {
-            var target = new PriorityValue<string>(Owner, TestProperty, NullSink);
+            var target = new PriorityValue<string>(Owner, TestProperty, ValueStore);
             var source1 = new Source("1");
             var source2 = new Source("2");
             var source3 = new Source("3");
@@ -310,16 +310,5 @@ namespace Avalonia.Base.UnitTests
 
             public void OnCompleted() => _observer.OnCompleted();
         }
-
-        private class MockSink : IValueSink
-        {
-            public void Completed<T>(StyledPropertyBase<T> property, IPriorityValueEntry entry, Optional<T> oldValue)
-            {
-            }
-
-            public void ValueChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
-            {
-            }
-        }
     }
 }

tests/Avalonia.Base.UnitTests/Styling/SetterTests.cs

@@ -5,6 +5,7 @@ using Avalonia.Controls;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
 using Avalonia.Data.Converters;
+using Avalonia.Diagnostics;
 using Avalonia.Styling;
 using Moq;
 using Xunit;
@@ -105,51 +106,51 @@ namespace Avalonia.Base.UnitTests.Styling
         [Fact]
         public void Setter_Should_Apply_Value_With_Activator_As_Binding_With_StyleTrigger_Priority()
         {
-            var control = new Mock<IStyleable>();
-            var style = Mock.Of<Style>();
+            var control = new Canvas();
             var setter = new Setter(TextBlock.TagProperty, "foo");
-            var activator = new Subject<bool>();
 
-            var instance = setter.Instance(control.Object);
+            var instance = setter.Instance(control);
             instance.Start(true);
             instance.Activate();
 
-            control.Verify(x => x.Bind(
-                TextBlock.TagProperty,
-                It.IsAny<IObservable<BindingValue<object>>>(),
-                BindingPriority.StyleTrigger));
+            Assert.Equal("foo", control.Tag);
+            Assert.Equal(BindingPriority.StyleTrigger, control.GetDiagnostic(TextBlock.TagProperty).Priority);
         }
 
         [Fact]
         public void Setter_Should_Apply_Binding_Without_Activator_With_Style_Priority()
         {
-            var control = new Mock<IStyleable>();
-            var style = Mock.Of<Style>();
-            var setter = new Setter(TextBlock.TagProperty, CreateMockBinding(TextBlock.TagProperty));
+            var control = new Canvas();
+            var source = new { Foo = "foo" };
+            var setter = new Setter(TextBlock.TagProperty, new Binding
+            {
+                Source = source,
+                Path = nameof(source.Foo),
+            });
 
-            setter.Instance(control.Object).Start(false);
+            setter.Instance(control).Start(false);
 
-            control.Verify(x => x.Bind(
-                TextBlock.TagProperty,
-                It.IsAny<PropertySetterBindingInstance<object>>(),
-                BindingPriority.Style));
+            Assert.Equal("foo", control.Tag);
+            Assert.Equal(BindingPriority.Style, control.GetDiagnostic(TextBlock.TagProperty).Priority);
         }
 
         [Fact]
         public void Setter_Should_Apply_Binding_With_Activator_With_StyleTrigger_Priority()
         {
-            var control = new Mock<IStyleable>();
-            var style = Mock.Of<Style>();
-            var setter = new Setter(TextBlock.TagProperty, CreateMockBinding(TextBlock.TagProperty));
+            var control = new Canvas();
+            var source = new { Foo = "foo" };
+            var setter = new Setter(TextBlock.TagProperty, new Binding
+            {
+                Source = source,
+                Path = nameof(source.Foo),
+            });
 
-            var instance = setter.Instance(control.Object);
+            var instance = setter.Instance(control);
             instance.Start(true);
             instance.Activate();
 
-            control.Verify(x => x.Bind(
-                TextBlock.TagProperty,
-                It.IsAny<IObservable<BindingValue<object>>>(),
-                BindingPriority.StyleTrigger));
+            Assert.Equal("foo", control.Tag);
+            Assert.Equal(BindingPriority.StyleTrigger, control.GetDiagnostic(TextBlock.TagProperty).Priority);
         }
 
         private IBinding CreateMockBinding(AvaloniaProperty property)

tests/Avalonia.Benchmarks/Visuals/VisualAffectsRenderBenchmarks.cs

@@ -0,0 +1,45 @@
+using Avalonia.Controls;
+using Avalonia.Media;
+using BenchmarkDotNet.Attributes;
+
+namespace Avalonia.Benchmarks.Visuals;
+
+[MemoryDiagnoser]
+public class VisualAffectsRenderBenchmarks
+{
+    private readonly TestVisual _target;
+    private readonly IPen _pen;
+        
+    public VisualAffectsRenderBenchmarks()
+    {
+        _target = new TestVisual();
+        _pen = new Pen(Brushes.Black);
+    }
+        
+    [Benchmark]
+    public void SetPropertyThatAffectsRender()
+    {
+        _target.Pen = _pen;
+        _target.Pen = null;
+    }
+
+    private class TestVisual : Visual
+    {
+        /// <summary>
+        /// Defines the <see cref="Pen"/> property.
+        /// </summary>
+        public static readonly StyledProperty<IPen> PenProperty =
+            AvaloniaProperty.Register<Border, IPen>(nameof(Pen));
+            
+        public IPen Pen
+        {
+            get => GetValue(PenProperty);
+            set => SetValue(PenProperty, value);
+        }
+
+        static TestVisual()
+        {
+            AffectsRender<TestVisual>(PenProperty);
+        }
+    }
+}