Refactor TopLevel and ItemsRepeater handling.

src/Avalonia.Controls/Repeater/ItemsRepeater.cs

@@ -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;
@@ -68,25 +69,25 @@ namespace Avalonia.Controls
         private ItemsRepeaterElementPreparedEventArgs? _elementPreparedArgs;
         private ItemsRepeaterElementClearingEventArgs? _elementClearingArgs;
         private ItemsRepeaterElementIndexChangedEventArgs? _elementIndexChangedArgs;
-        private WeakEventSubscriber<EventArgs> _layoutWeakSubscriber = new();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ItemsRepeater"/> class.
         /// </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);
-            
-            _layoutWeakSubscriber.Event += (_, ev, e) =>
-            {
-                if (ev == AttachedLayout.ArrangeInvalidatedWeakEvent)
-                    InvalidateArrange();
-                else if (ev == AttachedLayout.MeasureInvalidatedWeakEvent)
-                    InvalidateMeasure();
-            };
-            
+
             OnLayoutChanged(null, Layout);
         }
 

src/Avalonia.Controls/TopLevel.cs

@@ -91,7 +91,7 @@ namespace Avalonia.Controls
         private WindowTransparencyLevel _actualTransparencyLevel;
         private ILayoutManager? _layoutManager;
         private Border? _transparencyFallbackBorder;
-        private WeakEventSubscriber<ResourcesChangedEventArgs>? _resourcesChangesSubscriber;
+        private TargetWeakEventSubscriber<TopLevel, ResourcesChangedEventArgs>? _resourcesChangesSubscriber;
 
         /// <summary>
         /// Initializes static members of the <see cref="TopLevel"/> class.
@@ -191,11 +191,12 @@ namespace Avalonia.Controls
 
             if (((IStyleHost)this).StylingParent is IResourceHost applicationResources)
             {
-                _resourcesChangesSubscriber = new();
-                _resourcesChangesSubscriber.Event += (_, __, e) =>
-                {
-                    ((ILogical)this).NotifyResourcesChanged(e);
-                };
+                _resourcesChangesSubscriber = new TargetWeakEventSubscriber<TopLevel, ResourcesChangedEventArgs>(
+                    this, static (target, _, _, e) =>
+                    {
+                        ((ILogical)target).NotifyResourcesChanged(e);
+                    });
+
                 ResourcesChangedWeakEvent.Subscribe(applicationResources, _resourcesChangesSubscriber);
             }