Don't implement IWeakEventSubscriber directly on public types

src/Avalonia.Base/Utilities/IWeakEventSubscriber.cs

@@ -9,4 +9,14 @@ namespace Avalonia.Utilities;
 public interface IWeakEventSubscriber<in TEventArgs> where TEventArgs : EventArgs
 {
     void OnEvent(object? sender, WeakEvent ev, TEventArgs e);
+}
+
+public 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)
+    {
+        
+    }
 }

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.
@@ -68,6 +68,7 @@ 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.
@@ -77,6 +78,15 @@ namespace Avalonia.Controls
             _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);
         }
 
@@ -723,8 +733,8 @@ 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)
@@ -742,8 +752,8 @@ 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;
@@ -793,15 +803,7 @@ 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/TopLevel.cs

@@ -33,8 +33,7 @@ namespace Avalonia.Controls
         ICloseable,
         IStyleHost,
         ILogicalRoot,
-        ITextInputMethodRoot,
-        IWeakEventSubscriber<ResourcesChangedEventArgs>
+        ITextInputMethodRoot
     {
         /// <summary>
         /// Defines the <see cref="ClientSize"/> property.
@@ -90,6 +89,7 @@ namespace Avalonia.Controls
         private WindowTransparencyLevel _actualTransparencyLevel;
         private ILayoutManager _layoutManager;
         private Border _transparencyFallbackBorder;
+        private WeakEventSubscriber<ResourcesChangedEventArgs> _resourcesChangesSubscriber;
 
         /// <summary>
         /// Initializes static members of the <see cref="TopLevel"/> class.
@@ -184,7 +184,12 @@ namespace Avalonia.Controls
 
             if (((IStyleHost)this).StylingParent is IResourceHost applicationResources)
             {
-                ResourcesChangedWeakEvent.Subscribe(applicationResources, this);
+                _resourcesChangesSubscriber = new();
+                _resourcesChangesSubscriber.Event += (_, __, e) =>
+                {
+                    ((ILogical)this).NotifyResourcesChanged(e);
+                };
+                ResourcesChangedWeakEvent.Subscribe(applicationResources, _resourcesChangesSubscriber);
             }
 
             impl.LostFocus += PlatformImpl_LostFocus;
@@ -289,11 +294,6 @@ 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.Visuals/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 WeakEventSubscriber<EventArgs>? _weakSubscriber;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="Pen"/> class.
         /// </summary>
@@ -207,13 +208,23 @@ 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 WeakEventSubscriber<EventArgs>();
+                    _weakSubscriber.Event += (_, ev, __) =>
+                    {
+                        if (ev == InvalidatedWeakEvent)
+                            _invalidated?.Invoke(this, EventArgs.Empty);
+                    };
+                }
+                InvalidatedWeakEvent.Subscribe(affectsRender, _weakSubscriber);
                 field = affectsRender;
             }
         }
@@ -223,11 +234,5 @@ 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);
-        }
     }
 }