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();
@@ -172,6 +177,7 @@ public void Bind(DataTemplate template, object bindingContext, ItemsView itemsVi
 
 				// Set the binding context _before_ we create the renderer; that way, it's available during OnElementChanged
 				view.BindingContext = bindingContext;
+				_bound = true;
 
 				var renderer = TemplateHelpers.GetHandler(view, itemsView.FindMauiContext());
 				SetRenderer(renderer);
@@ -190,13 +196,12 @@ public void Bind(DataTemplate template, object bindingContext, ItemsView itemsVi
 				if (oldElement != null)
 				{
 					oldElement.BindingContext = bindingContext;
-					oldElement.MeasureInvalidated += MeasureInvalidated;
-
-					UpdateCellSize();
+					_bound = true;
 				}
 			}
 
 			CurrentTemplate = itemTemplate;
+			((IMauiPlatformView)this).InvalidateMeasure();
 		}
 
 		void SetRenderer(IPlatformViewHandler renderer)
@@ -211,8 +216,6 @@ void SetRenderer(IPlatformViewHandler renderer)
 			InitializeContentConstraints(platformView);
 
 			UpdateVisualStates();
-
-			(renderer.VirtualView as View).MeasureInvalidated += MeasureInvalidated;
 		}
 
 		void ClearSubviews()
@@ -230,7 +233,9 @@ internal void UseContent(TemplatedCell measurementCell)
 			ConstrainedSize = measurementCell.ConstrainedSize;
 			CurrentTemplate = measurementCell.CurrentTemplate;
 			_size = measurementCell._size;
+			_bound = true;
 			SetRenderer(measurementCell.PlatformHandler);
+			((IMauiPlatformView)this).InvalidateMeasure();
 		}
 
 		bool IsUsingVSMForSelectionColor(View view)
@@ -280,20 +285,30 @@ 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 +359,10 @@ void UpdateSelectionColor(View view)
 				SelectedBackgroundView.BackgroundColor = UIColor.Clear;
 			}
 		}
+
+		void IMauiPlatformView.InvalidateAncestorsMeasuresWhenMovedToWindow()
+		{
+			// This is a no-op for cells
+		}
 	}
 }

src/Controls/src/Core/ILegacyChildMeasureInvalidated.cs

@@ -0,0 +1,10 @@
+using System;
+using Microsoft.Maui.Controls.Internals;
+
+namespace Microsoft.Maui.Controls;
+
+[Obsolete("This is part of the legacy layout system and will be removed in a future release")]
+internal interface ILegacyChildMeasureInvalidated
+{
+	void OnChildMeasureInvalidated(VisualElement child, InvalidationTrigger trigger);
+}

src/Controls/src/Core/LegacyLayouts/Layout.cs

@@ -90,7 +90,7 @@ Size ILayoutManager.ArrangeChildren(Rect bounds)
 	/// Base class for layouts that allow you to arrange and group UI controls in your application.
 	/// </summary>
 	[Obsolete("Use Microsoft.Maui.Controls.Layout instead. For more information, see https://learn.microsoft.com/dotnet/maui/user-interface/layouts/custom")]
-	public abstract class Layout : View, ILayout, ILayoutController, IPaddingElement, IView, IVisualTreeElement, IInputTransparentContainerElement
+	public abstract class Layout : View, ILayout, ILayoutController, IPaddingElement, IView, IVisualTreeElement, IInputTransparentContainerElement, ILegacyChildMeasureInvalidated
 	{
 		/// <summary>Bindable property for <see cref="IsClippedToBounds"/>.</summary>
 		public static readonly BindableProperty IsClippedToBoundsProperty =
@@ -196,16 +196,16 @@ private protected override IList<Element> LogicalChildrenInternalBackingStore
 #pragma warning disable CS0672 // Member overrides obsolete member
 #pragma warning disable CS0618 // Type or member is obsolete
 		public override SizeRequest Measure(double widthConstraint, double heightConstraint, MeasureFlags flags = MeasureFlags.None)
-#pragma warning restore CS0618 // Type or member is obsolete
 		{
-#pragma warning disable CS0618 // Type or member is obsolete
 			SizeRequest size = base.Measure(widthConstraint - Padding.HorizontalThickness, heightConstraint - Padding.VerticalThickness, flags);
-#pragma warning restore CS0618 // Type or member is obsolete
-#pragma warning disable CS0618 // Type or member is obsolete
-			return new SizeRequest(new Size(size.Request.Width + Padding.HorizontalThickness, size.Request.Height + Padding.VerticalThickness),
-				new Size(size.Minimum.Width + Padding.HorizontalThickness, size.Minimum.Height + Padding.VerticalThickness));
-#pragma warning restore CS0618 // Type or member is obsolete
+			var request = new Size(size.Request.Width + Padding.HorizontalThickness, size.Request.Height + Padding.VerticalThickness);
+			var minimum = new Size(size.Minimum.Width + Padding.HorizontalThickness, size.Minimum.Height + Padding.VerticalThickness);
+
+			DesiredSize = request;
+
+			return new SizeRequest(request, minimum);
 		}
+#pragma warning restore CS0618 // Type or member is obsolete
 #pragma warning restore CS0672 // Member overrides obsolete member
 
 		/// <summary>
@@ -320,14 +320,19 @@ public void RaiseChild(View view)
 		[Obsolete("Use InvalidateMeasure depending on your scenario")]
 		protected virtual void InvalidateLayout()
 		{
-			_hasDoneLayout = false;
+			SetNeedsLayout();
 			InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
 			if (!_hasDoneLayout)
 			{
 				ForceLayout();
 			}
 		}
 
+		private void SetNeedsLayout()
+		{
+			_hasDoneLayout = false;
+		}
+
 		/// <summary>
 		/// Positions and sizes the children of a layout.
 		/// </summary>
@@ -341,10 +346,16 @@ protected virtual void InvalidateLayout()
 		[Obsolete("Use ArrangeOverride")]
 		protected abstract void LayoutChildren(double x, double y, double width, double height);
 
-		internal override void OnChildMeasureInvalidatedInternal(VisualElement child, InvalidationTrigger trigger)
+		[Obsolete("This method will be removed in the next major release.")]
+		void ILegacyChildMeasureInvalidated.OnChildMeasureInvalidated(VisualElement child, InvalidationTrigger trigger)
 		{
-			// TODO: once we remove old Xamarin public signatures we can invoke `OnChildMeasureInvalidated(VisualElement, InvalidationTrigger)` directly
+			SetNeedsLayout();
+			InvalidateMeasureCache();
+
 			OnChildMeasureInvalidated(child, new InvalidationEventArgs(trigger));
+
+			var propagatedTrigger = trigger == InvalidationTrigger.RendererReady ? trigger : InvalidationTrigger.MeasureChanged;
+			(Parent as ILegacyChildMeasureInvalidated)?.OnChildMeasureInvalidated(this, propagatedTrigger);
 		}
 
 		/// <summary>
@@ -356,8 +367,6 @@ internal override void OnChildMeasureInvalidatedInternal(VisualElement child, In
 		/// <remarks>This method has a default implementation and application developers must call the base implementation.</remarks>
 		protected void OnChildMeasureInvalidated(object sender, EventArgs e)
 		{
-			InvalidationTrigger trigger = (e as InvalidationEventArgs)?.Trigger ?? InvalidationTrigger.Undefined;
-			OnChildMeasureInvalidated((VisualElement)sender, trigger);
 			OnChildMeasureInvalidated();
 		}
 
@@ -531,42 +540,6 @@ internal static void LayoutChildIntoBoundingRegion(View child, Rect region, Size
 			child.Layout(region);
 		}
 
-		internal virtual void OnChildMeasureInvalidated(VisualElement child, InvalidationTrigger trigger)
-		{
-			IReadOnlyList<Element> children = LogicalChildrenInternal;
-			int count = children.Count;
-			for (var index = 0; index < count; index++)
-			{
-				if (LogicalChildrenInternal[index] is VisualElement v && v.IsVisible && (!v.IsPlatformEnabled || !v.IsPlatformStateConsistent))
-				{
-					return;
-				}
-			}
-
-			if (child is View view)
-			{
-				// we can ignore the request if we are either fully constrained or when the size request changes and we were already fully constrained
-				if ((trigger == InvalidationTrigger.MeasureChanged && view.Constraint == LayoutConstraint.Fixed) ||
-					(trigger == InvalidationTrigger.SizeRequestChanged && view.ComputedConstraint == LayoutConstraint.Fixed))
-				{
-					return;
-				}
-				if (trigger == InvalidationTrigger.HorizontalOptionsChanged || trigger == InvalidationTrigger.VerticalOptionsChanged)
-				{
-					ComputeConstraintForView(view);
-				}
-			}
-
-			if (trigger == InvalidationTrigger.RendererReady)
-			{
-				InvalidateMeasureInternal(InvalidationTrigger.RendererReady);
-			}
-			else
-			{
-				InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
-			}
-		}
-
 		internal override void OnIsVisibleChanged(bool oldValue, bool newValue)
 		{
 			base.OnIsVisibleChanged(oldValue, newValue);
@@ -677,19 +650,6 @@ bool ShouldLayoutChildren()
 			return true;
 		}
 
-		protected override void InvalidateMeasureOverride()
-		{
-			base.InvalidateMeasureOverride();
-
-			foreach (var child in ((IElementController)this).LogicalChildren)
-			{
-				if (child is IView fe)
-				{
-					fe.InvalidateMeasure();
-				}
-			}
-		}
-
 		protected override Size ArrangeOverride(Rect bounds)
 		{
 			base.ArrangeOverride(bounds);