Fix for PathGeometry.Figures.Clear() leaks when clearing shared PathFigure instances

src/Controls/src/Core/Shapes/PathGeometry.cs

@@ -14,6 +14,11 @@ namespace Microsoft.Maui.Controls.Shapes
 	[ContentProperty("Figures")]
 	public sealed class PathGeometry : Geometry
 	{
+		// Tracks figures whose PropertyChanged and InvalidatePathSegmentRequested events are
+		// subscribed so we can unsubscribe them even when the collection is cleared (Reset
+		// action does not populate OldItems).
+		readonly List<PathFigure> _subscribedFigures = new List<PathFigure>();
+
 		/// <summary>
 		/// Initializes a new instance of the <see cref="PathGeometry"/> class.
 		/// </summary>
@@ -198,17 +203,36 @@ void AddPolyQuad(PathF path, PolyQuadraticBezierSegment polyQuadraticBezierSegme
 			}
 		}
 
+		void SubscribeFigure(PathFigure figure)
+		{
+			figure.PropertyChanged += OnPathFigurePropertyChanged;
+			figure.InvalidatePathSegmentRequested += OnInvalidatePathSegmentRequested;
+			_subscribedFigures.Add(figure);
+		}
+
+		void UnsubscribeFigure(PathFigure figure)
+		{
+			figure.PropertyChanged -= OnPathFigurePropertyChanged;
+			figure.InvalidatePathSegmentRequested -= OnInvalidatePathSegmentRequested;
+			_subscribedFigures.Remove(figure);
+		}
+
+		void UnsubscribeAllFigures()
+		{
+			foreach (var figure in _subscribedFigures)
+			{
+				figure.PropertyChanged -= OnPathFigurePropertyChanged;
+				figure.InvalidatePathSegmentRequested -= OnInvalidatePathSegmentRequested;
+			}
+			_subscribedFigures.Clear();
+		}
+
 		void UpdatePathFigureCollection(PathFigureCollection oldCollection, PathFigureCollection newCollection)
 		{
 			if (oldCollection != null)
 			{
 				oldCollection.CollectionChanged -= OnPathFigureCollectionChanged;
-
-				foreach (var oldPathFigure in oldCollection)
-				{
-					oldPathFigure.PropertyChanged -= OnPathFigurePropertyChanged;
-					oldPathFigure.InvalidatePathSegmentRequested -= OnInvalidatePathSegmentRequested;
-				}
+				UnsubscribeAllFigures();
 			}
 
 			if (newCollection == null)
@@ -218,34 +242,37 @@ void UpdatePathFigureCollection(PathFigureCollection oldCollection, PathFigureCo
 
 			foreach (var newPathFigure in newCollection)
 			{
-				newPathFigure.PropertyChanged += OnPathFigurePropertyChanged;
-				newPathFigure.InvalidatePathSegmentRequested += OnInvalidatePathSegmentRequested;
+				SubscribeFigure(newPathFigure);
 			}
 		}
 
 		void OnPathFigureCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
 		{
-			if (e.OldItems != null)
+			if (e.OldItems != null && e.Action != NotifyCollectionChangedAction.Move)
 			{
 				foreach (var oldItem in e.OldItems)
 				{
-					if (!(oldItem is PathFigure oldPathFigure))
-						continue;
-
-					oldPathFigure.PropertyChanged -= OnPathFigurePropertyChanged;
-					oldPathFigure.InvalidatePathSegmentRequested -= OnInvalidatePathSegmentRequested;
+					if (oldItem is PathFigure oldPathFigure)
+					{
+						UnsubscribeFigure(oldPathFigure);
+					}
 				}
 			}
+			if (e.Action == NotifyCollectionChangedAction.Reset)
+			{
+				// Clear() raises Reset with OldItems = null; unsubscribe all tracked figures
+				// to prevent the cleared figures from retaining this PathGeometry alive.
+				UnsubscribeAllFigures();
+			}
 
-			if (e.NewItems != null)
+			if (e.NewItems != null && e.Action != NotifyCollectionChangedAction.Move)
 			{
 				foreach (var newItem in e.NewItems)
 				{
-					if (!(newItem is PathFigure newPathFigure))
-						continue;
-
-					newPathFigure.PropertyChanged += OnPathFigurePropertyChanged;
-					newPathFigure.InvalidatePathSegmentRequested += OnInvalidatePathSegmentRequested;
+					if (newItem is PathFigure newPathFigure)
+					{
+						SubscribeFigure(newPathFigure);
+					}
 				}
 			}
 

src/Controls/tests/Core.UnitTests/Shapes/PathGeometryTests.cs

@@ -0,0 +1,94 @@
+using System;
+using System.Runtime.CompilerServices;
+using Microsoft.Maui.Controls.Shapes;
+using Microsoft.Maui.Graphics;
+using Xunit;
+
+namespace Microsoft.Maui.Controls.Core.UnitTests.Shapes;
+
+public class PathGeometryTests : BaseTestFixture
+{
+	/// <summary>
+	/// Figures.Clear() must unsubscribe the cleared PathFigure from the PathGeometry,
+	/// otherwise the figure retains the geometry alive via its PropertyChanged delegate.
+	/// </summary>
+	[Fact]
+	public void FiguresClear_UnsubscribesFigurePropertyChangedHandler()
+	{
+		var geometry = new PathGeometry();
+		var sharedFigure = new PathFigure { StartPoint = new Point(0, 0) };
+		geometry.Figures.Add(sharedFigure);
+
+		int invalidateCount = 0;
+		geometry.InvalidatePathGeometryRequested += (s, e) => invalidateCount++;
+
+		// Sanity-check: mutating the figure before Clear should trigger invalidation.
+		sharedFigure.StartPoint = new Point(10, 10);
+		Assert.Equal(1, invalidateCount);
+
+		// Act - Clear() fires CollectionChanged (Reset), which itself calls Invalidate() once.
+		geometry.Figures.Clear();
+		int countAfterClear = invalidateCount;
+
+		// After Clear, mutating the figure must NOT trigger any further invalidation on the geometry.
+		sharedFigure.StartPoint = new Point(20, 20);
+		Assert.Equal(countAfterClear, invalidateCount);
+	}
+
+	/// <summary>
+	/// Figures.Clear() must unsubscribe the cleared PathFigure's segment-invalidation event
+	/// from the PathGeometry.
+	/// </summary>
+	[Fact]
+	public void FiguresClear_UnsubscribesFigureSegmentInvalidateHandler()
+	{
+		var geometry = new PathGeometry();
+		var sharedFigure = new PathFigure { StartPoint = new Point(0, 0) };
+		geometry.Figures.Add(sharedFigure);
+
+		int invalidateCount = 0;
+		geometry.InvalidatePathGeometryRequested += (s, e) => invalidateCount++;
+
+		// Sanity-check: adding a segment before Clear should trigger invalidation.
+		sharedFigure.Segments.Add(new LineSegment { Point = new Point(100, 100) });
+		Assert.Equal(1, invalidateCount);
+
+		// Act - Clear() fires CollectionChanged (Reset), which itself calls Invalidate() once.
+		geometry.Figures.Clear();
+		int countAfterClear = invalidateCount;
+
+		// After Clear, adding segments to the cleared figure must NOT trigger any further invalidation.
+		sharedFigure.Segments.Add(new LineSegment { Point = new Point(200, 200) });
+		Assert.Equal(countAfterClear, invalidateCount);
+	}
+
+	/// <summary>
+	/// After Figures.Clear(), the PathGeometry must be eligible for garbage collection
+	/// even when the cleared PathFigure is still alive (shared/rooted elsewhere).
+	/// </summary>
+	[Fact]
+	public void FiguresClear_AllowsPathGeometryToBeGarbageCollected()
+	{
+		var sharedFigure = new PathFigure { StartPoint = new Point(0, 0) };
+		var weakRef = CreateGeometryAndClear(sharedFigure);
+
+		GC.Collect();
+		GC.WaitForPendingFinalizers();
+		GC.Collect();
+
+		// If the bug is present, sharedFigure still holds the geometry alive via
+		// its PropertyChanged delegate chain, so TryGetTarget would return true.
+		Assert.False(weakRef.TryGetTarget(out _),
+			"PathGeometry was retained by the cleared PathFigure (event-handler leak in Figures.Clear()).");
+	}
+
+	// Factored out so the JIT cannot inline the PathGeometry local onto the caller's frame.
+	[MethodImpl(MethodImplOptions.NoInlining)]
+	static WeakReference<PathGeometry> CreateGeometryAndClear(PathFigure figure)
+	{
+		var geometry = new PathGeometry();
+		geometry.Figures.Add(figure);
+		geometry.Figures.Clear();
+		return new WeakReference<PathGeometry>(geometry);
+	}
+}