[ios] fix memory leaks in ContentView

Context: https://github.com/jonathanpeppers/MemoryLeaksOniOS
Related to: dotnet#14664

There are a couple cycles on iOS that causes memory leaks in all
controls based on `ContentView`:

* `Microsoft.Maui.Controls.ContentView` ->
    * `ContentViewHandler` ->
    * `Microsoft.Maui.Platform` ->
    * `CrossPlatformArrange/Measure` property ->
* `Microsoft.Maui.Controls.ContentView` cycle

To fix this, I made `CrossPlatformArrange/Measure` properties obsolete,
using the weak `View` property directly instead. This applies to various
other controls like `Border`, `RadioButton`, `SwipeItemView`, `SwipeView`.

I did not yet fix `ScrollView` that appears to be more complicated to
solve. For now, it supports both code paths.

`ScrollView` will continue to have leaks in:

* Closures with captured variables
    * https://github.com/dotnet/maui/blob/3b620952425ca3c4542c4632e05d09eb4f583e22/src/Core/src/Handlers/ScrollView/ScrollViewHandler.iOS.cs#L195
    * https://github.com/dotnet/maui/blob/3b620952425ca3c4542c4632e05d09eb4f583e22/src/Core/src/Handlers/ScrollView/ScrollViewHandler.iOS.cs#L227

* `CrossPlatformArrange/Measure`
    * https://github.com/dotnet/maui/blob/3b620952425ca3c4542c4632e05d09eb4f583e22/src/Core/src/Handlers/ScrollView/ScrollViewHandler.iOS.cs#L182-L186

src/Controls/src/Core/Compatibility/Handlers/iOS/FrameRenderer.cs

@@ -51,9 +51,7 @@ protected override void OnElementChanged(ElementChangedEventArgs<Frame> e)
 
 			if (e.NewElement != null)
 			{
-				_actualView.CrossPlatformArrange = (e.NewElement as IContentView).CrossPlatformArrange;
-				_actualView.CrossPlatformMeasure = (e.NewElement as IContentView).CrossPlatformMeasure;
-
+				_actualView.View = e.NewElement;
 				SetupLayer();
 				UpdateShadow();
 			}

src/Controls/tests/DeviceTests/Elements/ContentView/ContentViewTests.cs

@@ -76,5 +76,42 @@ await InvokeOnMainThreadAsync(() =>
 				Assert.True(child.BindingContext == bindingContext);
 			});
 		}
+
+		[Fact(DisplayName = "ContentView Does Not Leak")]
+		public async Task DoesNotLeak()
+		{
+			SetupBuilder();
+			WeakReference viewReference = null;
+			WeakReference handlerReference = null;
+			WeakReference platformReference = null;
+
+			{
+				var view = new Microsoft.Maui.Controls.ContentView();
+				var page = new ContentPage { Content = view };
+				await CreateHandlerAndAddToWindow(page, () =>
+				{
+					viewReference = new(view);
+					handlerReference = new(view.Handler);
+					platformReference = new(view.Handler.PlatformView);
+					page.Content = null;
+				});
+			}
+
+			Assert.NotNull(viewReference);
+			Assert.NotNull(platformReference);
+			Assert.NotNull(handlerReference);
+
+			// Multiple GCs are sometimes required on iOS
+			for (int i = 0; i < 3; i++)
+			{
+				await Task.Yield();
+				GC.Collect();
+				GC.WaitForPendingFinalizers();
+			}
+
+			Assert.False(viewReference.IsAlive, "View should not be alive!");
+			Assert.False(handlerReference.IsAlive, "Handler should not be alive!");
+			Assert.False(platformReference.IsAlive, "PlatformView should not be alive!");
+		}
 	}
 }

src/Controls/tests/DeviceTests/Elements/NavigationPage/NavigationPageTests.cs

@@ -36,6 +36,7 @@ void SetupBuilder()
 					handlers.AddHandler<Frame, FrameRenderer>();
 					handlers.AddHandler<Label, LabelHandler>();
 					handlers.AddHandler<Button, ButtonHandler>();
+					handlers.AddHandler<ContentView, ContentViewHandler>();
 					handlers.AddHandler<CollectionView, CollectionViewHandler>();
 				});
 			});
@@ -269,6 +270,7 @@ await CreateHandlerAndAddToWindow<WindowHandlerStub>(new Window(navPage), async
 					{
 						new Label(),
 						new Button(),
+						new ContentView(),
 						new CollectionView(),
 					}
 				};

src/Controls/tests/DeviceTests/Elements/Shell/ShellTests.cs

@@ -16,6 +16,7 @@
 using Microsoft.Maui.Hosting;
 using Microsoft.Maui.Platform;
 using Xunit;
+using ContentView = Microsoft.Maui.Controls.ContentView;
 
 #if ANDROID || IOS || MACCATALYST
 using ShellHandler = Microsoft.Maui.Controls.Handlers.Compatibility.ShellRenderer;
@@ -40,6 +41,7 @@ void SetupBuilder()
 					SetupShellHandlers(handlers);
 					handlers.AddHandler(typeof(NavigationPage), typeof(NavigationViewHandler));
 					handlers.AddHandler(typeof(Button), typeof(ButtonHandler));
+					handlers.AddHandler(typeof(ContentView), typeof(ContentViewHandler));
 					handlers.AddHandler(typeof(CollectionView), typeof(CollectionViewHandler));
 				});
 			});
@@ -982,6 +984,7 @@ await CreateHandlerAndAddToWindow<ShellHandler>(shell, async (handler) =>
 					{
 						new Label(),
 						new Button(),
+						new ContentView(),
 						new CollectionView(),
 					}
 				};

src/Core/src/Handlers/Border/BorderHandler.iOS.cs

@@ -12,11 +12,7 @@ protected override ContentView CreatePlatformView()
 			_ = VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} must be set to create a {nameof(ContentView)}");
 			_ = MauiContext ?? throw new InvalidOperationException($"{nameof(MauiContext)} cannot be null");
 
-			return new ContentView
-			{
-				CrossPlatformMeasure = VirtualView.CrossPlatformMeasure,
-				CrossPlatformArrange = VirtualView.CrossPlatformArrange
-			};
+			return new ContentView { View = VirtualView };
 		}
 
 		protected override void ConnectHandler(ContentView platformView)
@@ -40,8 +36,6 @@ public override void SetVirtualView(IView view)
 			_ = VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} should have been set by base class.");
 
 			PlatformView.View = view;
-			PlatformView.CrossPlatformMeasure = VirtualView.CrossPlatformMeasure;
-			PlatformView.CrossPlatformArrange = VirtualView.CrossPlatformArrange;
 		}
 
 		static void UpdateContent(IBorderHandler handler)

src/Core/src/Handlers/ContentView/ContentViewHandler.iOS.cs

@@ -10,11 +10,7 @@ protected override ContentView CreatePlatformView()
 			_ = VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} must be set to create a {nameof(ContentView)}");
 			_ = MauiContext ?? throw new InvalidOperationException($"{nameof(MauiContext)} cannot be null");
 
-			return new ContentView
-			{
-				CrossPlatformMeasure = VirtualView.CrossPlatformMeasure,
-				CrossPlatformArrange = VirtualView.CrossPlatformArrange
-			};
+			return new ContentView { View = VirtualView };
 		}
 
 		public override void SetVirtualView(IView view)
@@ -24,8 +20,6 @@ public override void SetVirtualView(IView view)
 			_ = VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} should have been set by base class.");
 
 			PlatformView.View = view;
-			PlatformView.CrossPlatformMeasure = VirtualView.CrossPlatformMeasure;
-			PlatformView.CrossPlatformArrange = VirtualView.CrossPlatformArrange;
 		}
 
 		static void UpdateContent(IContentViewHandler handler)
@@ -56,8 +50,6 @@ public static void MapContent(IContentViewHandler handler, IContentView page)
 
 		protected override void DisconnectHandler(ContentView platformView)
 		{
-			platformView.CrossPlatformMeasure = null;
-			platformView.CrossPlatformArrange = null;
 			platformView.RemoveFromSuperview();
 			base.DisconnectHandler(platformView);
 		}

src/Core/src/Handlers/RadioButton/RadioButtonHandler.iOS.cs

@@ -19,8 +19,6 @@ public override void SetVirtualView(IView view)
 			_ = VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} should have been set by base class.");
 
 			PlatformView.View = view;
-			PlatformView.CrossPlatformMeasure = VirtualView.CrossPlatformMeasure;
-			PlatformView.CrossPlatformArrange = VirtualView.CrossPlatformArrange;
 		}
 
 		static void UpdateContent(IRadioButtonHandler handler)

src/Core/src/Handlers/ScrollView/ScrollViewHandler.iOS.cs

@@ -179,11 +179,15 @@ static void InsertContentView(UIScrollView platformScrollView, IScrollView scrol
 			var contentContainer = new ContentView()
 			{
 				View = scrollView.PresentedContent,
+#pragma warning disable CS0618 // Type or member is obsolete
 				CrossPlatformMeasure = ConstrainToScrollView(scrollView.CrossPlatformMeasure, platformScrollView, scrollView),
+#pragma warning restore CS0618
 				Tag = ContentPanelTag
 			};
 
+#pragma warning disable CS0618 // Type or member is obsolete
 			contentContainer.CrossPlatformArrange = ArrangeScrollViewContent(scrollView.CrossPlatformArrange, contentContainer, platformScrollView, scrollView);
+#pragma warning restore CS0618
 
 			platformScrollView.ClearSubviews();
 			contentContainer.AddSubview(platformContent);

src/Core/src/Handlers/SwipeItemView/SwipeItemViewHandler.iOS.cs

@@ -5,24 +5,7 @@ namespace Microsoft.Maui.Handlers
 {
 	public partial class SwipeItemViewHandler : ViewHandler<ISwipeItemView, ContentView>, ISwipeItemViewHandler
 	{
-		protected override ContentView CreatePlatformView()
-		{
-			return new ContentView
-			{
-				CrossPlatformMeasure = VirtualView.CrossPlatformMeasure,
-				CrossPlatformArrange = VirtualView.CrossPlatformArrange
-			};
-		}
-
-		public override void SetVirtualView(IView view)
-		{
-			base.SetVirtualView(view);
-			_ = VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} should have been set by base class.");
-			_ = PlatformView ?? throw new InvalidOperationException($"{nameof(PlatformView)} should have been set by base class.");
-
-			PlatformView.CrossPlatformMeasure = VirtualView.CrossPlatformMeasure;
-			PlatformView.CrossPlatformArrange = VirtualView.CrossPlatformArrange;
-		}
+		protected override ContentView CreatePlatformView() => new ContentView { View = VirtualView };
 
 		void UpdateContent()
 		{

src/Core/src/Handlers/SwipeView/SwipeViewHandler.iOS.cs

@@ -10,9 +10,7 @@ protected override MauiSwipeView CreatePlatformView()
 		{
 			return new MauiSwipeView
 			{
-				CrossPlatformMeasure = VirtualView.CrossPlatformMeasure,
-				CrossPlatformArrange = VirtualView.CrossPlatformArrange,
-				Element = VirtualView
+				View = VirtualView
 			};
 		}
 
@@ -21,9 +19,7 @@ public override void SetVirtualView(IView view)
 			base.SetVirtualView(view);
 			_ = PlatformView ?? throw new InvalidOperationException($"{nameof(PlatformView)} should have been set by base class.");
 
-			PlatformView.Element = VirtualView;
-			PlatformView.CrossPlatformMeasure = VirtualView.CrossPlatformMeasure;
-			PlatformView.CrossPlatformArrange = VirtualView.CrossPlatformArrange;
+			PlatformView.View = VirtualView;
 		}
 
 		public static void MapContent(ISwipeViewHandler handler, ISwipeView view)

src/Core/src/Platform/iOS/ContentView.cs

@@ -19,15 +19,24 @@ public ContentView()
 
 		public override CGSize SizeThatFits(CGSize size)
 		{
-			if (CrossPlatformMeasure == null)
+#pragma warning disable CS0618 // Type or member is obsolete
+			var crossPlatformMeasure = CrossPlatformMeasure;
+#pragma warning restore CS0618 // Type or member is obsolete
+
+			if (crossPlatformMeasure is null && View is IContentView view)
+			{
+				crossPlatformMeasure = view.CrossPlatformMeasure;
+			}
+
+			if (crossPlatformMeasure is null)
 			{
 				return base.SizeThatFits(size);
 			}
 
 			var widthConstraint = size.Width;
 			var heightConstraint = size.Height;
 
-			var crossPlatformSize = CrossPlatformMeasure(widthConstraint, heightConstraint);
+			var crossPlatformSize = crossPlatformMeasure(widthConstraint, heightConstraint);
 
 			CacheMeasureConstraints(widthConstraint, heightConstraint);
 
@@ -38,6 +47,26 @@ public override void LayoutSubviews()
 		{
 			base.LayoutSubviews();
 
+#pragma warning disable CS0618 // Type or member is obsolete
+			var crossPlatformMeasure = CrossPlatformMeasure;
+			var crossPlatformArrange = CrossPlatformArrange;
+#pragma warning restore CS0618 // Type or member is obsolete
+
+			var view = View as IContentView;
+			if (crossPlatformMeasure is null && view is not null)
+			{
+				crossPlatformMeasure = view.CrossPlatformMeasure;
+			}
+			if (crossPlatformArrange is null && view is not null)
+			{
+				crossPlatformArrange = view.CrossPlatformArrange;
+			}
+
+			if (crossPlatformMeasure is null || crossPlatformArrange is null)
+			{
+				return;
+			}
+
 			var bounds = AdjustForSafeArea(Bounds).ToRectangle();
 			var widthConstraint = bounds.Width;
 			var heightConstraint = bounds.Height;
@@ -49,11 +78,11 @@ public override void LayoutSubviews()
 
 			if (!IsMeasureValid(widthConstraint, heightConstraint) && Superview is not MauiView)
 			{
-				CrossPlatformMeasure?.Invoke(widthConstraint, heightConstraint);
+				crossPlatformMeasure(widthConstraint, heightConstraint);
 				CacheMeasureConstraints(widthConstraint, heightConstraint);
 			}
 
-			CrossPlatformArrange?.Invoke(bounds);
+			crossPlatformArrange(bounds);
 
 			if (ChildMaskLayer != null)
 				ChildMaskLayer.Frame = bounds;
@@ -70,7 +99,9 @@ public override void SetNeedsLayout()
 			Superview?.SetNeedsLayout();
 		}
 
+		[Obsolete("Use View instead. This member causes memory leaks.")]
 		internal Func<double, double, Size>? CrossPlatformMeasure { get; set; }
+		[Obsolete("Use View instead. This member causes memory leaks.")]
 		internal Func<Rect, Size>? CrossPlatformArrange { get; set; }
 
 		internal IBorderStroke? Clip

src/Core/src/Platform/iOS/MauiSwipeView.cs

@@ -33,7 +33,7 @@ public class MauiSwipeView : ContentView
 		bool _isResettingSwipe;
 		bool _isOpen;
 		OpenSwipeItem _previousOpenSwipeItem;
-		internal ISwipeView? Element { get; set; }
+		internal ISwipeView? Element => View as ISwipeView;
 
 		public MauiSwipeView()
 		{

src/Core/src/Platform/iOS/PageViewController.cs

@@ -13,14 +13,7 @@ public PageViewController(IView page, IMauiContext mauiContext)
 			LoadFirstView(page);
 		}
 
-		protected override UIView CreatePlatformView(IElement view)
-		{
-			return new ContentView
-			{
-				CrossPlatformArrange = ((IContentView)view).CrossPlatformArrange,
-				CrossPlatformMeasure = ((IContentView)view).CrossPlatformMeasure
-			};
-		}
+		protected override UIView CreatePlatformView(IElement view) => new ContentView { View = (IContentView)view };
 
 		public override void TraitCollectionDidChange(UITraitCollection? previousTraitCollection)
 		{

src/Core/src/Platform/iOS/SemanticSwitchContentView.cs

@@ -14,8 +14,7 @@ internal class SemanticSwitchContentView : ContentView
 
 	internal SemanticSwitchContentView(IContentView virtualView)
 	{
-		CrossPlatformMeasure = virtualView.CrossPlatformMeasure;
-		CrossPlatformArrange = virtualView.CrossPlatformArrange;
+		View = virtualView;
 		IsAccessibilityElement = true;
 	}
 

src/Core/src/PublicAPI/net-ios/PublicAPI.Shipped.txt

@@ -2103,7 +2103,6 @@ override Microsoft.Maui.Handlers.StepperHandler.CreatePlatformView() -> UIKit.UI
 override Microsoft.Maui.Handlers.StepperHandler.DisconnectHandler(UIKit.UIStepper! platformView) -> void
 override Microsoft.Maui.Handlers.SwipeItemMenuItemHandler.CreatePlatformElement() -> UIKit.UIButton!
 override Microsoft.Maui.Handlers.SwipeItemViewHandler.CreatePlatformView() -> Microsoft.Maui.Platform.ContentView!
-override Microsoft.Maui.Handlers.SwipeItemViewHandler.SetVirtualView(Microsoft.Maui.IView! view) -> void
 override Microsoft.Maui.Handlers.SwipeViewHandler.CreatePlatformView() -> Microsoft.Maui.Platform.MauiSwipeView!
 override Microsoft.Maui.Handlers.SwipeViewHandler.SetVirtualView(Microsoft.Maui.IView! view) -> void
 override Microsoft.Maui.Handlers.SwitchHandler.ConnectHandler(UIKit.UISwitch! platformView) -> void

src/Core/src/PublicAPI/net-maccatalyst/PublicAPI.Shipped.txt

@@ -2102,7 +2102,6 @@ override Microsoft.Maui.Handlers.StepperHandler.CreatePlatformView() -> UIKit.UI
 override Microsoft.Maui.Handlers.StepperHandler.DisconnectHandler(UIKit.UIStepper! platformView) -> void
 override Microsoft.Maui.Handlers.SwipeItemMenuItemHandler.CreatePlatformElement() -> UIKit.UIButton!
 override Microsoft.Maui.Handlers.SwipeItemViewHandler.CreatePlatformView() -> Microsoft.Maui.Platform.ContentView!
-override Microsoft.Maui.Handlers.SwipeItemViewHandler.SetVirtualView(Microsoft.Maui.IView! view) -> void
 override Microsoft.Maui.Handlers.SwipeViewHandler.CreatePlatformView() -> Microsoft.Maui.Platform.MauiSwipeView!
 override Microsoft.Maui.Handlers.SwipeViewHandler.SetVirtualView(Microsoft.Maui.IView! view) -> void
 override Microsoft.Maui.Handlers.SwitchHandler.ConnectHandler(UIKit.UISwitch! platformView) -> void