Add new event handlers to base behaviors

src/Avalonia.Xaml.Interactions.Custom/Core/BindingTriggerBehavior.cs

@@ -108,25 +108,35 @@ protected override void OnDetaching()
 
     private static void OnValueChanged(AvaloniaPropertyChangedEventArgs args)
     {
-        if (args.Sender is not BindingTriggerBehavior behavior || behavior.AssociatedObject is null)
+        if (args.Sender is not BindingTriggerBehavior behavior)
         {
             return;
         }
 
-        if (!behavior.IsEnabled)
+        behavior.Execute(parameter: args);
+    }
+
+    private void Execute(object? parameter)
+    {
+        if (AssociatedObject is null)
+        {
+            return;
+        }
+
+        if (!IsEnabled)
         {
             return;
         }
 
         // NOTE: In UWP version binding null check is not present but Avalonia throws exception as Bindings are null when first initialized.
-        var binding = behavior.BindingValue;
+        var binding = BindingValue;
         if (binding is not null)
         {
             // Some value has changed--either the binding value, reference value, or the comparison condition. Re-evaluate the equation.
-            if (ComparisonConditionTypeHelper.Compare(behavior.BindingValue, behavior.ComparisonCondition,
-                    behavior.Value))
+            if (ComparisonConditionTypeHelper.Compare(BindingValue, ComparisonCondition,
+                    Value))
             {
-                Interaction.ExecuteActions(behavior.AssociatedObject, behavior.Actions, args);
+                Interaction.ExecuteActions(AssociatedObject, Actions, parameter);
             }
         }
     }

src/Avalonia.Xaml.Interactions/Core/DataTriggerBehavior.cs

@@ -1,4 +1,5 @@
-using System.Diagnostics.CodeAnalysis;
+using System;
+using System.Diagnostics.CodeAnalysis;
 using Avalonia.Reactive;
 using Avalonia.Xaml.Interactivity;
 
@@ -69,24 +70,34 @@ static DataTriggerBehavior()
 
     private static void OnValueChanged(AvaloniaPropertyChangedEventArgs args)
     {
-        if (args.Sender is not DataTriggerBehavior behavior || behavior.AssociatedObject is null)
+        if (args.Sender is not DataTriggerBehavior behavior)
         {
             return;
         }
 
-        if (!behavior.IsEnabled)
+        behavior.Execute(parameter: args);
+    }
+
+    private void Execute(object? parameter)
+    {        
+        if (AssociatedObject is null)
+        {
+            return;
+        }
+
+        if (!IsEnabled)
         {
             return;
         }
 
         // NOTE: In UWP version binding null check is not present but Avalonia throws exception as Bindings are null when first initialized.
-        var binding = behavior.Binding;
+        var binding = Binding;
         if (binding is not null)
         {
             // Some value has changed--either the binding value, reference value, or the comparison condition. Re-evaluate the equation.
-            if (ComparisonConditionTypeHelper.Compare(behavior.Binding, behavior.ComparisonCondition, behavior.Value))
+            if (ComparisonConditionTypeHelper.Compare(Binding, ComparisonCondition, Value))
             {
-                Interaction.ExecuteActions(behavior.AssociatedObject, behavior.Actions, args);
+                Interaction.ExecuteActions(AssociatedObject, Actions, parameter);
             }
         }
     }

src/Avalonia.Xaml.Interactivity/Behavior.cs

@@ -97,11 +97,19 @@ protected virtual void OnDetaching()
 
     void IBehaviorEventsHandler.UnloadedEventHandler() => OnUnloaded();
 
+    void IBehaviorEventsHandler.InitializedEventHandler() => OnInitializedEvent();
+
+    void IBehaviorEventsHandler.DataContextChangedEventHandler() => OnDataContextChangedEvent();
+
+    void IBehaviorEventsHandler.ResourcesChangedEventHandler() => OnResourcesChangedEvent();
+
+    void IBehaviorEventsHandler.ActualThemeVariantChangedEventHandler() => OnActualThemeVariantChangedEvent();
+
     /// <summary>
     /// Called after the <see cref="AssociatedObject"/> is attached to the visual tree.
     /// </summary>
     /// <remarks>
-    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="Control"/>.
+    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="Visual"/>.
     /// </remarks>
     protected virtual void OnAttachedToVisualTree()
     {
@@ -111,7 +119,7 @@ protected virtual void OnAttachedToVisualTree()
     /// Called when the <see cref="AssociatedObject"/> is being detached from the visual tree.
     /// </summary>
     /// <remarks>
-    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="Control"/>.
+    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="Visual"/>.
     /// </remarks>
     protected virtual void OnDetachedFromVisualTree()
     {
@@ -121,7 +129,7 @@ protected virtual void OnDetachedFromVisualTree()
     /// Called after the <see cref="AssociatedObject"/> is attached to the logical tree.
     /// </summary>
     /// <remarks>
-    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="Control"/>.
+    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="StyledElement"/>.
     /// </remarks>
     protected virtual void OnAttachedToLogicalTree()
     {
@@ -131,7 +139,7 @@ protected virtual void OnAttachedToLogicalTree()
     /// Called when the <see cref="AssociatedObject"/> is being detached from the logical tree.
     /// </summary>
     /// <remarks>
-    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="Control"/>.
+    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="StyledElement"/>.
     /// </remarks>
     protected virtual void OnDetachedFromLogicalTree()
     {
@@ -156,4 +164,44 @@ protected virtual void OnLoaded()
     protected virtual void OnUnloaded()
     {
     }
+
+    /// <summary>
+    /// Called when the <see cref="AssociatedObject"/> is initialized.
+    /// </summary>
+    /// <remarks>
+    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="StyledElement"/>.
+    /// </remarks>
+    protected virtual void OnInitializedEvent()
+    {
+    }
+
+    /// <summary>
+    /// Called when the <see cref="AssociatedObject"/> DataContext changed.
+    /// </summary>
+    /// <remarks>
+    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="StyledElement"/>.
+    /// </remarks>
+    protected virtual void OnDataContextChangedEvent()
+    {
+    }
+
+    /// <summary>
+    /// Called when the <see cref="AssociatedObject"/> Resources changed.
+    /// </summary>
+    /// <remarks>
+    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="StyledElement"/>.
+    /// </remarks>
+    protected virtual void OnResourcesChangedEvent()
+    {
+    }
+
+    /// <summary>
+    /// Called when the <see cref="AssociatedObject"/> ActualThemeVariant changed.
+    /// </summary>
+    /// <remarks>
+    /// Invoked only when the <see cref="AssociatedObject"/> is of type <see cref="StyledElement"/>.
+    /// </remarks>
+    protected virtual void OnActualThemeVariantChangedEvent()
+    {
+    }
 }

src/Avalonia.Xaml.Interactivity/BehaviorCollection.cs

@@ -145,6 +145,50 @@ internal void Unloaded()
         }
     }
 
+    internal void Initialized()
+    {
+        foreach (var item in this)
+        {
+            if (item is IBehaviorEventsHandler behaviorEventsHandler and IBehavior { AssociatedObject: not null })
+            {
+                behaviorEventsHandler.InitializedEventHandler();
+            }
+        }
+    }
+
+    internal void DataContextChanged()
+    {
+        foreach (var item in this)
+        {
+            if (item is IBehaviorEventsHandler behaviorEventsHandler and IBehavior { AssociatedObject: not null })
+            {
+                behaviorEventsHandler.DataContextChangedEventHandler();
+            }
+        }
+    }
+
+    internal void ResourcesChanged()
+    {
+        foreach (var item in this)
+        {
+            if (item is IBehaviorEventsHandler behaviorEventsHandler and IBehavior { AssociatedObject: not null })
+            {
+                behaviorEventsHandler.ResourcesChangedEventHandler();
+            }
+        }
+    }
+
+    internal void ActualThemeVariantChanged()
+    {
+        foreach (var item in this)
+        {
+            if (item is IBehaviorEventsHandler behaviorEventsHandler and IBehavior { AssociatedObject: not null })
+            {
+                behaviorEventsHandler.ActualThemeVariantChangedEventHandler();
+            }
+        }
+    }
+
     private void BehaviorCollection_CollectionChanged(object? sender, NotifyCollectionChangedEventArgs eventArgs)
     {
         if (eventArgs.Action == NotifyCollectionChangedAction.Reset)

src/Avalonia.Xaml.Interactivity/IBehaviorEventsHandler.cs

@@ -34,4 +34,24 @@ public interface IBehaviorEventsHandler
     /// Called when element is unloaded.
     /// </summary>
     void UnloadedEventHandler();
+
+    /// <summary>
+    /// Called when element is initialized.
+    /// </summary>
+    void InitializedEventHandler();
+
+    /// <summary>
+    /// Called when element DataContext changed.
+    /// </summary>
+    void DataContextChangedEventHandler();
+
+    /// <summary>
+    /// Called when element Resources changed.
+    /// </summary>
+    void ResourcesChangedEventHandler();
+
+    /// <summary>
+    /// Called when element ActualThemeVariant changed.
+    /// </summary>
+    void ActualThemeVariantChangedEventHandler();
 }