perf(memory): Reduce ConditionalDisposable pressure

- Remove indirect delegates created from `ConditionalDisposable`
- Use strong references for property changes registrations to avoid the creation of `ConditionalDisposable` instances
- If `RegisterPropertyChangedCallback` is used and is registered on self, don't use `DispatcherConditionalDisposable`
- Generate `OnPropertyChanged2` for all uno-internal DependencyObject to avoid delegates creation. DependencyObject now invokes this method through `IDependencyObjectInternal`.

src/SourceGenerators/Uno.UI.SourceGenerators/DependencyObject/DependencyObjectGenerator.cs

@@ -48,6 +48,7 @@ private class SerializationMethodsGenerator : SymbolVisitor
 			private readonly INamedTypeSymbol? _bindableAttributeSymbol;
 			private readonly INamedTypeSymbol? _iFrameworkElementSymbol;
 			private readonly INamedTypeSymbol? _frameworkElementSymbol;
+			private readonly bool _isUnoSolution;
 
 			public SerializationMethodsGenerator(GeneratorExecutionContext context)
 			{
@@ -66,6 +67,7 @@ public SerializationMethodsGenerator(GeneratorExecutionContext context)
 				_bindableAttributeSymbol = comp.GetTypeByMetadataName("Windows.UI.Xaml.Data.BindableAttribute");
 				_iFrameworkElementSymbol = comp.GetTypeByMetadataName(XamlConstants.Types.IFrameworkElement);
 				_frameworkElementSymbol = comp.GetTypeByMetadataName("Windows.UI.Xaml.FrameworkElement");
+				_isUnoSolution = _context.GetMSBuildPropertyValue("_IsUnoUISolution") == "true";
 			}
 
 			public override void VisitNamedType(INamedTypeSymbol type)
@@ -116,7 +118,7 @@ private void ProcessType(INamedTypeSymbol typeSymbol)
 
 				if (isDependencyObject)
 				{
-					if (_context.GetMSBuildPropertyValue("_IsUnoUISolution") != "true")
+					if (!_isUnoSolution)
 					{
 						if (typeSymbol.Is(_iosViewSymbol))
 						{
@@ -162,9 +164,11 @@ private void ProcessType(INamedTypeSymbol typeSymbol)
 								builder.AppendLineInvariant(@"[global::Windows.UI.Xaml.Data.Bindable]");
 							}
 
-							using (builder.BlockInvariant($"partial class {typeSymbol.Name} : IDependencyObjectStoreProvider, IWeakReferenceProvider"))
+							var internalDependencyObject = _isUnoSolution && !typeSymbol.IsSealed ? ", IDependencyObjectInternal" : "";
+
+							using (builder.BlockInvariant($"partial class {typeSymbol.Name} : IDependencyObjectStoreProvider, IWeakReferenceProvider{internalDependencyObject}"))
 							{
-								GenerateDependencyObjectImplementation(builder);
+								GenerateDependencyObjectImplementation(typeSymbol, builder);
 								GenerateIBinderImplementation(typeSymbol, builder);
 							}
 						}
@@ -851,7 +855,7 @@ public override bool Equals(object other)
 				}
 			}
 
-			private static void GenerateDependencyObjectImplementation(IndentedStringBuilder builder)
+			private void GenerateDependencyObjectImplementation(INamedTypeSymbol typeSymbol, IndentedStringBuilder builder)
 			{
 				builder.AppendLineInvariant(@"private DependencyObjectStore __storeBackingField;");
 				builder.AppendLineInvariant(@"public Windows.UI.Core.CoreDispatcher Dispatcher => Windows.ApplicationModel.Core.CoreApplication.MainView.Dispatcher;");
@@ -890,6 +894,16 @@ private static void GenerateDependencyObjectImplementation(IndentedStringBuilder
 				builder.AppendLineInvariant("public long RegisterPropertyChangedCallback(DependencyProperty dp, DependencyPropertyChangedCallback callback) => __Store.RegisterPropertyChangedCallback(dp, callback);");
 
 				builder.AppendLineInvariant("public void UnregisterPropertyChangedCallback(DependencyProperty dp, long token) => __Store.UnregisterPropertyChangedCallback(dp, token);");
+
+				if (_isUnoSolution && !typeSymbol.IsSealed)
+				{
+					builder.AppendLineInvariant("void IDependencyObjectInternal.OnPropertyChanged2(global::Windows.UI.Xaml.DependencyPropertyChangedEventArgs args) => OnPropertyChanged2(args);");
+
+					if (typeSymbol.GetMethodsWithName("OnPropertyChanged2").None(m => m.Parameters.Length == 1))
+					{
+						builder.AppendLineInvariant("internal virtual void OnPropertyChanged2(global::Windows.UI.Xaml.DependencyPropertyChangedEventArgs args) {{ }}");
+					}
+				}
 			}
 		}
 	}

src/Uno.Foundation/Uno.Core.Extensions/Uno.Core.Extensions.Disposables/Disposables/ConditionalDisposable.cs

@@ -26,11 +26,10 @@ namespace Uno.Disposables
 	/// <summary>
 	/// A disposable that can call an action when a dependent object has been collected.
 	/// </summary>
-	internal class ConditionalDisposable : IDisposable
+	internal abstract class ConditionalDisposable : IDisposable
 	{
 		private static ConditionalWeakTable<object, List<IDisposable>> _registrations = new ConditionalWeakTable<object, List<IDisposable>>();
 
-		private readonly Action _action;
 		private bool _disposed;
 		private readonly WeakReference? _conditionSource;
 		private readonly List<IDisposable> _list;
@@ -43,12 +42,10 @@ internal class ConditionalDisposable : IDisposable
 		/// Creates a <see cref="ConditionalDisposable"/> instance using 
 		/// <paramref name="target"/> as a reference for its lifetime.
 		/// </summary>
-		/// <param name="action">The action to be executed when target has been collected</param>
 		/// <param name="conditionSource">An optional secondary reference, used to avoid calling action if it has been collected</param>
 		/// <param name="target">The instance to use to keep the disposable alive</param>
-		public ConditionalDisposable(object target, Action action, WeakReference? conditionSource = null)
+		public ConditionalDisposable(object target, WeakReference? conditionSource = null)
 		{
-			_action = action;
 			_conditionSource = conditionSource;
 
 #if DEBUG
@@ -74,6 +71,8 @@ public void Dispose()
 			Dispose(true);
 		}
 
+		protected abstract void TargetFinalized();
+
 		private void Dispose(bool disposing)
 		{
 			if(disposing)
@@ -94,7 +93,7 @@ private void Dispose(bool disposing)
 					{
 						_disposed = true;
 
-						_action();
+						TargetFinalized();
 					}
 				}
 			}
@@ -105,5 +104,4 @@ private void Dispose(bool disposing)
 			Dispose(false);
 		}
 	}
-
 }

src/Uno.UI/UI/Xaml/Controls/DropDownButton/DropDownButton.cs

@@ -27,11 +27,19 @@ protected override void OnApplyTemplate()
 		{
 			base.OnApplyTemplate();
 
-			this.RegisterDisposablePropertyChangedCallback(Button.FlyoutProperty, OnFlyoutPropertyChanged);
-
 			RegisterFlyoutEvents();
 		}
 
+		internal override void OnPropertyChanged2(DependencyPropertyChangedEventArgs args)
+		{
+			if (args.Property == Button.FlyoutProperty)
+			{
+				OnFlyoutPropertyChanged(this, args);
+			}
+
+			base.OnPropertyChanged2(args);
+		}
+
 		private void RegisterFlyoutEvents()
 		{
 			if (Flyout != null)

src/Uno.UI/UI/Xaml/Controls/Grid/ColumnDefinition.cs

@@ -15,11 +15,14 @@ public ColumnDefinition()
 		{
 			InitializeBinder();
 			IsAutoPropertyInheritanceEnabled = false;
+		}
 
-			this.RegisterDisposablePropertyChangedCallback((i, p, args) =>
-			{
-				InvalidateDefinition();
-			});
+		/// <remarks>
+		/// This method is called from the generated IDependencyObjectInternal.OnPropertyChanged2 method
+		/// </summary>
+		internal void OnPropertyChanged2(DependencyPropertyChangedEventArgs args)
+		{
+			InvalidateDefinition();
 		}
 
 		#region Width DependencyProperty

src/Uno.UI/UI/Xaml/Controls/Grid/RowDefinition.cs

@@ -14,11 +14,14 @@ public RowDefinition()
 		{
 			InitializeBinder();
 			IsAutoPropertyInheritanceEnabled = false;
+		}
 
-			this.RegisterDisposablePropertyChangedCallback((i, p, args) =>
-			{
-				InvalidateDefinition();
-			});
+		/// <remarks>
+		/// This method is called from the generated IDependencyObjectInternal.OnPropertyChanged2 method
+		/// </summary>
+		internal void OnPropertyChanged2(DependencyPropertyChangedEventArgs args)
+		{
+			InvalidateDefinition();
 		}
 
 		#region Height DependencyProperty

src/Uno.UI/UI/Xaml/Controls/ScrollContentPresenter/ScrollContentPresenter.cs

@@ -69,7 +69,7 @@ bool IScrollContentPresenter.ForceChangeToCurrentView
 
 		private void InitializeScrollContentPresenter()
 		{
-			this.RegisterParentChangedCallback(this, OnParentChanged);
+			this.RegisterParentChangedCallbackStrong(this, OnParentChanged);
 		}
 
 		private void OnParentChanged(object instance, object key, DependencyObjectParentChangedEventArgs args)

src/Uno.UI/UI/Xaml/Controls/TextBox/TextBox.cs

@@ -82,7 +82,7 @@ public partial class TextBox : Control, IFrameworkTemplatePoolAware
 
 		public TextBox()
 		{
-			this.RegisterParentChangedCallback(this, OnParentChanged);
+			this.RegisterParentChangedCallbackStrong(this, OnParentChanged);
 
 			DefaultStyleKey = typeof(TextBox);
 			SizeChanged += OnSizeChanged;

src/Uno.UI/UI/Xaml/DependencyObjectExtensions.cs

@@ -400,6 +400,16 @@ internal static IDisposable RegisterParentChangedCallback(this DependencyObject
 			return GetStore(instance).RegisterParentChangedCallback(key, handler);
 		}
 
+		/// <summary>
+		/// Registers to parent changes.
+		/// </summary>
+		/// <param name="instance">The target dependency object</param>
+		/// <param name="key">A key to be passed to the callback parameter.</param>
+		/// <param name="handler">A callback to be called</param>
+		/// <returns>A disposable that cancels the subscription.</returns>
+		internal static void RegisterParentChangedCallbackStrong(this DependencyObject instance, object key, ParentChangedCallback handler)
+			=> GetStore(instance).RegisterParentChangedCallback(key, handler);
+
 		/// <summary>
 		/// Determines if the specified dependency property is set.
 		/// A property is set whenever a value (including null) is assigned to it.