Remove MeasureInvalidated propagation on non-legacy layouts

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

@@ -99,6 +99,8 @@ void IMauiPlatformView.InvalidateAncestorsMeasuresWhenMovedToWindow()
 			_invalidateParentWhenMovedToWindow = true;
 		}
 
+		void IMauiPlatformView.InvalidateMeasure() => SetNeedsLayout();
+
 		public override void MovedToWindow()
 		{
 			base.MovedToWindow();

src/Controls/src/Core/Handlers/Items/iOS/ItemsViewController.cs

@@ -194,11 +194,30 @@ public override void ViewWillAppear(bool animated)
 		public override void ViewWillLayoutSubviews()
 		{
 			ConstrainItemsToBounds();
+			InvalidateLayoutIfItemsMeasureChanged();
 			base.ViewWillLayoutSubviews();
 			InvalidateMeasureIfContentSizeChanged();
 			LayoutEmptyView();
 		}
 
+		void InvalidateLayoutIfItemsMeasureChanged()
+		{
+			var visibleCells = CollectionView.VisibleCells;
+
+			var changed = false;
+			for (int n = 0; n < visibleCells.Length; n++)
+			{
+				if (visibleCells[n] is TemplatedCell { MeasureInvalidated: true } cell && cell.VerifyAndUpdateSize())
+				{
+					changed = true;
+				}
+			}
+
+			if (changed)
+			{
+				ItemsViewLayout.InvalidateLayout();
+			}
+		}
 
 
 		void MauiCollectionView.ICustomMauiCollectionViewDelegate.MovedToWindow(UIView view)
@@ -402,27 +421,14 @@ protected object GetItemAtIndex(NSIndexPath index)
 			return ItemsSource[index];
 		}
 
-		[UnconditionalSuppressMessage("Memory", "MEM0003", Justification = "Proven safe in test: CollectionViewTests.ItemsSourceDoesNotLeak")]
 		void CellContentSizeChanged(object sender, EventArgs e)
 		{
 			if (_disposed)
-				return;
-
-			if (!(sender is TemplatedCell cell))
 			{
 				return;
 			}
 
-			var visibleCells = CollectionView.VisibleCells;
-
-			for (int n = 0; n < visibleCells.Length; n++)
-			{
-				if (cell == visibleCells[n])
-				{
-					ItemsViewLayout?.InvalidateLayout();
-					return;
-				}
-			}
+			CollectionView.SetNeedsLayout();
 		}
 
 		[UnconditionalSuppressMessage("Memory", "MEM0003", Justification = "Proven safe in test: CollectionViewTests.ItemsSourceDoesNotLeak")]

src/Controls/src/Core/Handlers/Items/iOS/MauiCollectionView.cs

@@ -25,6 +25,11 @@ void IMauiPlatformView.InvalidateAncestorsMeasuresWhenMovedToWindow()
 		_invalidateParentWhenMovedToWindow = true;
 	}
 
+	void IMauiPlatformView.InvalidateMeasure()
+	{
+		// No-op during propagation
+	}
+
 	[UnconditionalSuppressMessage("Memory", "MEM0002", Justification = IUIViewLifeCycleEvents.UnconditionalSuppressMessage)]
 	EventHandler? _movedToWindow;
 

src/Controls/src/Core/Handlers/Items/iOS/TemplatedCell.cs

@@ -9,7 +9,7 @@
 
 namespace Microsoft.Maui.Controls.Handlers.Items
 {
-	public abstract class TemplatedCell : ItemsViewCell
+	public abstract class TemplatedCell : ItemsViewCell, IMauiPlatformView
 	{
 		readonly WeakEventManager _weakEventManager = new();
 
@@ -40,6 +40,7 @@ public DataTemplate CurrentTemplate
 		// Keep track of the cell size so we can verify whether a measure invalidation 
 		// actually changed the size of the cell
 		Size _size;
+		bool _bound;
 
 		internal CGSize CurrentSize => _size.ToCGSize();
 
@@ -50,6 +51,9 @@ protected TemplatedCell(CGRect frame) : base(frame)
 		}
 
 		WeakReference<IPlatformViewHandler> _handler;
+		bool _measureInvalidated;
+
+		internal bool MeasureInvalidated => _measureInvalidated;
 
 		internal IPlatformViewHandler PlatformHandler
 		{
@@ -77,9 +81,10 @@ protected void ClearConstraints()
 
 		internal void Unbind()
 		{
+			_bound = false;
+
 			if (PlatformHandler?.VirtualView is View view)
 			{
-				view.MeasureInvalidated -= MeasureInvalidated;
 				view.BindingContext = null;
 			}
 		}
@@ -120,6 +125,7 @@ CGSize UpdateCellSize()
 			var nativeBounds = platformView.Frame.ToRectangle();
 			PlatformHandler.VirtualView.Arrange(nativeBounds);
 			_size = nativeBounds.Size;
+			_measureInvalidated = false;
 
 			return size;
 		}
@@ -160,7 +166,6 @@ public void Bind(DataTemplate template, object bindingContext, ItemsView itemsVi
 				// Remove the old view, if it exists
 				if (oldElement != null)
 				{
-					oldElement.MeasureInvalidated -= MeasureInvalidated;
 					oldElement.BindingContext = null;
 					itemsView.RemoveLogicalChild(oldElement);
 					ClearSubviews();
@@ -190,13 +195,12 @@ public void Bind(DataTemplate template, object bindingContext, ItemsView itemsVi
 				if (oldElement != null)
 				{
 					oldElement.BindingContext = bindingContext;
-					oldElement.MeasureInvalidated += MeasureInvalidated;
-
-					UpdateCellSize();
 				}
 			}
 
 			CurrentTemplate = itemTemplate;
+			_bound = true;
+			((IMauiPlatformView)this).InvalidateMeasure();
 		}
 
 		void SetRenderer(IPlatformViewHandler renderer)
@@ -211,8 +215,6 @@ void SetRenderer(IPlatformViewHandler renderer)
 			InitializeContentConstraints(platformView);
 
 			UpdateVisualStates();
-
-			(renderer.VirtualView as View).MeasureInvalidated += MeasureInvalidated;
 		}
 
 		void ClearSubviews()
@@ -231,6 +233,8 @@ internal void UseContent(TemplatedCell measurementCell)
 			CurrentTemplate = measurementCell.CurrentTemplate;
 			_size = measurementCell._size;
 			SetRenderer(measurementCell.PlatformHandler);
+			_bound = true;
+			((IMauiPlatformView)this).InvalidateMeasure();
 		}
 
 		bool IsUsingVSMForSelectionColor(View view)
@@ -280,20 +284,30 @@ public override bool Selected
 
 		protected abstract (bool, Size) NeedsContentSizeUpdate(Size currentSize);
 
-		void MeasureInvalidated(object sender, EventArgs args)
+		void IMauiPlatformView.InvalidateMeasure()
+		{
+			// If the cell is not bound (or getting unbounded), we don't want to measure it
+			// and cause a useless and harming InvalidateLayout on the collection view layout
+			if (!_measureInvalidated && _bound)
+			{
+				_measureInvalidated = true;
+				OnContentSizeChanged();
+			}
+		}
+
+		internal bool VerifyAndUpdateSize()
 		{
+			_measureInvalidated = false;
 			var (needsUpdate, toSize) = NeedsContentSizeUpdate(_size);
 
 			if (!needsUpdate)
 			{
-				return;
+				return false;
 			}
 
 			// Cache the size for next time
 			_size = toSize;
-
-			// Let the controller know that things need to be arranged again
-			OnContentSizeChanged();
+			return true;
 		}
 
 		protected void OnContentSizeChanged()
@@ -344,5 +358,10 @@ void UpdateSelectionColor(View view)
 				SelectedBackgroundView.BackgroundColor = UIColor.Clear;
 			}
 		}
+
+		void IMauiPlatformView.InvalidateAncestorsMeasuresWhenMovedToWindow()
+		{
+			// This is a no-op for cells
+		}
 	}
 }

src/Controls/src/Core/Handlers/Items2/iOS/ItemsViewController2.cs

@@ -112,7 +112,7 @@ public override UICollectionViewCell GetCell(UICollectionView collectionView, NS
 			if (cell is TemplatedCell2 TemplatedCell2)
 			{
 				TemplatedCell2.ScrollDirection = ScrollDirection;
-
+				TemplatedCell2.Connect(CellContentSizeChanged);
 				TemplatedCell2.Bind(ItemsView.ItemTemplate, ItemsSource[indexpathAdjusted], ItemsView);
 			}
 			else if (cell is DefaultCell2 DefaultCell2)
@@ -188,10 +188,39 @@ public override void LoadView()
 
 		public override void ViewWillLayoutSubviews()
 		{
+			InvalidateLayoutIfItemsMeasureChanged();
 			base.ViewWillLayoutSubviews();
 			LayoutEmptyView();
 		}
 
+		void InvalidateLayoutIfItemsMeasureChanged()
+		{
+			var visibleCells = CollectionView.VisibleCells;
+			var changed = false;
+			for (int n = 0; n < visibleCells.Length; n++)
+			{
+				if (visibleCells[n] is TemplatedCell2 { MeasureInvalidated: true })
+				{
+					changed = true;
+				}
+			}
+
+			if (changed)
+			{
+				ItemsViewLayout.InvalidateLayout();
+			}
+		}
+
+		void CellContentSizeChanged(object sender, EventArgs e)
+		{
+			if (_disposed)
+			{
+				return;
+			}
+
+			CollectionView.SetNeedsLayout();
+		}
+
 		void Items.MauiCollectionView.ICustomMauiCollectionViewDelegate.MovedToWindow(UIView view)
 		{
 			if (CollectionView?.Window != null)