[ios] fix memory leak in Entry (#16349)

Context: #16346

This addresses the memory leak discovered by:

    src/Core/src/Platform/iOS/MauiTextField.cs(69,32): error MA0001: Event 'SelectionChanged' could cause memory leaks in an NSObject subclass. Remove the event or add the [UnconditionalSuppressMessage("Memory", "MA0001")] attribute with a justification as to why the event will not leak.
    src/Core/src/Platform/iOS/MauiTextField.cs(68,30): error MA0001: Event 'TextPropertySet' could cause memory leaks in an NSObject subclass. Remove the event or add the [UnconditionalSuppressMessage("Memory", "MA0001")] attribute with a justification as to why the event will not leak.

I could reproduce a leak in a test such as:

    await InvokeOnMainThreadAsync(() =>
    {
        var layout = new Grid();
        var entry = new Entry();
        layout.Add(entry);
        var handler = CreateHandler<LayoutHandler>(layout);
        viewReference = new WeakReference(entry);
        handlerReference = new WeakReference(entry.Handler);
        platformViewReference = new WeakReference(entry.Handler.PlatformView);
    });

    await AssertionExtensions.WaitForGC(viewReference, handlerReference, platformViewReference);
    Assert.False(viewReference.IsAlive, "Entry should not be alive!");
    Assert.False(handlerReference.IsAlive, "Handler should not be alive!");
    Assert.False(platformViewReference.IsAlive, "PlatformView should not be alive!");

Author: jonathanpeppers

src/Controls/tests/DeviceTests/Elements/Entry/EntryTests.cs

@@ -12,6 +12,17 @@ namespace Microsoft.Maui.DeviceTests
 	[Category(TestCategory.Entry)]
 	public partial class EntryTests : ControlsHandlerTestBase
 	{
+		void SetupBuilder()
+		{
+			EnsureHandlerCreated(builder =>
+			{
+				builder.ConfigureMauiHandlers(handlers =>
+				{
+					handlers.AddHandler<Entry, EntryHandler>();
+				});
+			});
+		}
+
 		[Fact]
 		public async Task MaxLengthTrims()
 		{
@@ -70,6 +81,32 @@ await InvokeOnMainThreadAsync(() =>
 			});
 		}
 
+		[Fact(DisplayName = "Does Not Leak")]
+		public async Task DoesNotLeak()
+		{
+			SetupBuilder();
+
+			WeakReference viewReference = null;
+			WeakReference platformViewReference = null;
+			WeakReference handlerReference = null;
+
+			await InvokeOnMainThreadAsync(() =>
+			{
+				var layout = new Grid();
+				var entry = new Entry();
+				layout.Add(entry);
+				var handler = CreateHandler<LayoutHandler>(layout);
+				viewReference = new WeakReference(entry);
+				handlerReference = new WeakReference(entry.Handler);
+				platformViewReference = new WeakReference(entry.Handler.PlatformView);
+			});
+
+			await AssertionExtensions.WaitForGC(viewReference, handlerReference, platformViewReference);
+			Assert.False(viewReference.IsAlive, "Entry should not be alive!");
+			Assert.False(handlerReference.IsAlive, "Handler should not be alive!");
+			Assert.False(platformViewReference.IsAlive, "PlatformView should not be alive!");
+		}
+
 #if WINDOWS
 		// Only Windows needs the IsReadOnly workaround for MaxLength==0 to prevent text from being entered
 		[Fact]

src/Core/src/Handlers/Entry/EntryHandler.iOS.cs

@@ -9,7 +9,7 @@ namespace Microsoft.Maui.Handlers
 {
 	public partial class EntryHandler : ViewHandler<IEntry, MauiTextField>
 	{
-		bool _set;
+		readonly MauiTextFieldProxy _proxy = new();
 
 		protected override MauiTextField CreatePlatformView() =>
 			new MauiTextField
@@ -22,35 +22,17 @@ public override void SetVirtualView(IView view)
 		{
 			base.SetVirtualView(view);
 
-			if (!_set)
-				PlatformView.SelectionChanged += OnSelectionChanged;
-
-			_set = true;
+			_proxy.SetVirtualView(PlatformView);
 		}
 
 		protected override void ConnectHandler(MauiTextField platformView)
 		{
-			platformView.ShouldReturn += OnShouldReturn;
-			platformView.EditingDidBegin += OnEditingBegan;
-			platformView.EditingChanged += OnEditingChanged;
-			platformView.EditingDidEnd += OnEditingEnded;
-			platformView.TextPropertySet += OnTextPropertySet;
-			platformView.ShouldChangeCharacters += OnShouldChangeCharacters;
+			_proxy.Connect(VirtualView, platformView);
 		}
 
 		protected override void DisconnectHandler(MauiTextField platformView)
 		{
-			platformView.ShouldReturn -= OnShouldReturn;
-			platformView.EditingDidBegin -= OnEditingBegan;
-			platformView.EditingChanged -= OnEditingChanged;
-			platformView.EditingDidEnd -= OnEditingEnded;
-			platformView.TextPropertySet -= OnTextPropertySet;
-			platformView.ShouldChangeCharacters -= OnShouldChangeCharacters;
-
-			if (_set)
-				platformView.SelectionChanged -= OnSelectionChanged;
-
-			_set = false;
+			_proxy.Disconnect(platformView);
 		}
 
 		public static void MapText(IEntryHandler handler, IEntry entry)
@@ -124,53 +106,112 @@ public static void MapFormatting(IEntryHandler handler, IEntry entry)
 			handler.PlatformView?.UpdateHorizontalTextAlignment(entry);
 		}
 
-		protected virtual bool OnShouldReturn(UITextField view)
+		protected virtual bool OnShouldReturn(UITextField view) =>
+			_proxy.OnShouldReturn(view);
+
+		class MauiTextFieldProxy
 		{
-			KeyboardAutoManager.GoToNextResponderOrResign(view);
+			bool _set;
+			WeakReference<IEntry>? _virtualView;
 
-			VirtualView?.Completed();
+			IEntry? VirtualView => _virtualView is not null && _virtualView.TryGetTarget(out var v) ? v : null;
 
-			return false;
-		}
+			public void Connect(IEntry virtualView, MauiTextField platformView)
+			{
+				_virtualView = new(virtualView);
 
-		void OnEditingBegan(object? sender, EventArgs e)
-		{
-			if (VirtualView == null || PlatformView == null)
-				return;
+				platformView.ShouldReturn += OnShouldReturn;
+				platformView.EditingDidBegin += OnEditingBegan;
+				platformView.EditingChanged += OnEditingChanged;
+				platformView.EditingDidEnd += OnEditingEnded;
+				platformView.TextPropertySet += OnTextPropertySet;
+				platformView.ShouldChangeCharacters += OnShouldChangeCharacters;
+			}
 
-			PlatformView?.UpdateSelectionLength(VirtualView);
+			public void Disconnect(MauiTextField platformView)
+			{
+				_virtualView = null;
 
-			VirtualView.IsFocused = true;
-		}
+				platformView.ShouldReturn -= OnShouldReturn;
+				platformView.EditingDidBegin -= OnEditingBegan;
+				platformView.EditingChanged -= OnEditingChanged;
+				platformView.EditingDidEnd -= OnEditingEnded;
+				platformView.TextPropertySet -= OnTextPropertySet;
+				platformView.ShouldChangeCharacters -= OnShouldChangeCharacters;
 
-		void OnEditingChanged(object? sender, EventArgs e) =>
-			VirtualView.UpdateText(PlatformView.Text);
+				if (_set)
+					platformView.SelectionChanged -= OnSelectionChanged;
 
-		void OnEditingEnded(object? sender, EventArgs e)
-		{
-			if (VirtualView == null || PlatformView == null)
-				return;
+				_set = false;
+			}
 
-			VirtualView.UpdateText(PlatformView.Text);
-			VirtualView.IsFocused = false;
-		}
+			public void SetVirtualView(MauiTextField platformView)
+			{
+				if (!_set)
+					platformView.SelectionChanged += OnSelectionChanged;
+				_set = true;
+			}
 
-		void OnTextPropertySet(object? sender, EventArgs e) =>
-			VirtualView.UpdateText(PlatformView.Text);
+			public bool OnShouldReturn(UITextField view)
+			{
+				KeyboardAutoManager.GoToNextResponderOrResign(view);
 
-		bool OnShouldChangeCharacters(UITextField textField, NSRange range, string replacementString) =>
-			VirtualView.TextWithinMaxLength(textField.Text, range, replacementString);
+				VirtualView?.Completed();
 
-		private void OnSelectionChanged(object? sender, EventArgs e)
-		{
-			var cursorPosition = PlatformView.GetCursorPosition();
-			var selectedTextLength = PlatformView.GetSelectedTextLength();
+				return false;
+			}
+
+			void OnEditingBegan(object? sender, EventArgs e)
+			{
+				if (sender is MauiTextField platformView && VirtualView is IEntry virtualView)
+				{
+					platformView.UpdateSelectionLength(virtualView);
+					virtualView.IsFocused = true;
+				}
+			}
+
+			void OnEditingChanged(object? sender, EventArgs e)
+			{
+				if (sender is MauiTextField platformView)
+				{
+					VirtualView?.UpdateText(platformView.Text);
+				}
+			}
 
-			if (VirtualView.CursorPosition != cursorPosition)
-				VirtualView.CursorPosition = cursorPosition;
+			void OnEditingEnded(object? sender, EventArgs e)
+			{
+				if (sender is MauiTextField platformView && VirtualView is IEntry virtualView)
+				{
+					virtualView.UpdateText(platformView.Text);
+					virtualView.IsFocused = false;
+				}
+			}
+
+			void OnTextPropertySet(object? sender, EventArgs e)
+			{
+				if (sender is MauiTextField platformView)
+				{
+					VirtualView?.UpdateText(platformView.Text);
+				}
+			}
 
-			if (VirtualView.SelectionLength != selectedTextLength)
-				VirtualView.SelectionLength = selectedTextLength;
+			bool OnShouldChangeCharacters(UITextField textField, NSRange range, string replacementString) =>
+				VirtualView?.TextWithinMaxLength(textField.Text, range, replacementString) ?? false;
+
+			void OnSelectionChanged(object? sender, EventArgs e)
+			{
+				if (sender is MauiTextField platformView && VirtualView is IEntry virtualView)
+				{
+					var cursorPosition = platformView.GetCursorPosition();
+					var selectedTextLength = platformView.GetSelectedTextLength();
+
+					if (virtualView.CursorPosition != cursorPosition)
+						virtualView.CursorPosition = cursorPosition;
+
+					if (virtualView.SelectionLength != selectedTextLength)
+						virtualView.SelectionLength = selectedTextLength;
+				}
+			}
 		}
 	}
 }

src/Core/src/Platform/iOS/MauiTextField.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using CoreGraphics;
 using Foundation;
 using ObjCRuntime;
@@ -65,7 +66,9 @@ public override UITextRange? SelectedTextRange
 			}
 		}
 
+		[UnconditionalSuppressMessage("Memory", "MA0001", Justification = "Proven safe in test: EntryTests.DoesNotLeak")]
 		public event EventHandler? TextPropertySet;
+		[UnconditionalSuppressMessage("Memory", "MA0001", Justification = "Proven safe in test: EntryTests.DoesNotLeak")]
 		internal event EventHandler? SelectionChanged;
 	}
 }