Fix TemplateBinding

src/Avalonia.Xaml.Interactivity/StyledElementAction.cs

@@ -34,12 +34,24 @@ public bool IsEnabled
 
     internal void AttachActionToLogicalTree(StyledElement parent)
     {
+        // Required for $parent binding in XAML
         ((ISetLogicalParent)this).SetParent(null);
         ((ISetLogicalParent)this).SetParent(parent);
+
+        // Required for TemplateBinding in XAML
+        if (parent.TemplatedParent is { } templatedParent)
+        {
+            TemplatedParentHelper.SetTemplatedParent(this, templatedParent);
+        }
     }
 
-    internal void DetachActionFromLogicalTree()
+    internal void DetachActionFromLogicalTree(StyledElement parent)
     {
         ((ISetLogicalParent)this).SetParent(null);
+
+        if (parent is { TemplatedParent: not null })
+        {
+            TemplatedParentHelper.SetTemplatedParent(this, null);
+        }
     }
 }

src/Avalonia.Xaml.Interactivity/StyledElementBehavior.cs

@@ -194,19 +194,32 @@ internal virtual void AttachBehaviorToLogicalTree()
             return;
         }
 
+        // Required for $parent binding in XAML
         ((ISetLogicalParent)this).SetParent(null);
         ((ISetLogicalParent)this).SetParent(styledElement);
+
+        // Required for TemplateBinding in XAML
+        if (styledElement.TemplatedParent is { } templatedParent)
+        {
+            TemplatedParentHelper.SetTemplatedParent(this, templatedParent);
+        }
     }
 
     internal virtual void DetachBehaviorFromLogicalTree()
     {
         ((ISetLogicalParent)this).SetParent(null);
+
+        if (AssociatedObject is StyledElement { TemplatedParent: not null })
+        {
+            TemplatedParentHelper.SetTemplatedParent(this, null);
+        }
     }
 
     private IDisposable? SynchronizeDataContext(AvaloniaObject associatedObject)
     {
         if (associatedObject is StyledElement styledElement)
         {
+            // Required for data context binding in XAML
             return styledElement
                 .GetObservable(DataContextProperty)
                 .Subscribe(new AnonymousObserver<object?>(x =>

src/Avalonia.Xaml.Interactivity/StyledElementTrigger.cs

@@ -43,14 +43,16 @@ internal override void AttachBehaviorToLogicalTree()
 
     internal override void DetachBehaviorFromLogicalTree()
     {
-        base.DetachBehaviorFromLogicalTree();
-        
+        var parent = this;
+
         foreach (var action in Actions)
         {
             if (action is StyledElementAction styledElementAction)
             {
-                styledElementAction.DetachActionFromLogicalTree();
+                styledElementAction.DetachActionFromLogicalTree(parent);
             }
         }
+
+        base.DetachBehaviorFromLogicalTree();
     }
 }

src/Avalonia.Xaml.Interactivity/TemplatedParentHelper.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Reflection;
+
+namespace Avalonia.Xaml.Interactivity;
+
+internal static class TemplatedParentHelper
+{
+    private static readonly Action<StyledElement, AvaloniaObject?>? s_setterDelegate;
+
+    static TemplatedParentHelper()
+    {
+        var templatedParentProperty = typeof(StyledElement).GetProperty(
+            "TemplatedParent",
+            BindingFlags.Public | BindingFlags.Instance);
+
+        var setMethod = templatedParentProperty?.GetSetMethod(true);
+        if (setMethod != null)
+        {
+            s_setterDelegate = (Action<StyledElement, AvaloniaObject?>)Delegate.CreateDelegate(
+                typeof(Action<StyledElement, AvaloniaObject?>),
+                setMethod);
+        }
+    }
+
+    public static void SetTemplatedParent(StyledElement target, AvaloniaObject? value)
+    {
+        s_setterDelegate?.Invoke(target, value);
+    }
+}