Stop iOS SetNeedsLayout propagation by looking at VisualElement computed Constraint

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

@@ -99,7 +99,11 @@ void IPlatformMeasureInvalidationController.InvalidateAncestorsMeasuresWhenMoved
 			_invalidateParentWhenMovedToWindow = true;
 		}
 
-		void IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating) => SetNeedsLayout();
+		bool IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
+		{
+			SetNeedsLayout();
+			return true;
+		}
 
 		public override void MovedToWindow()
 		{

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

@@ -28,14 +28,15 @@ void IPlatformMeasureInvalidationController.InvalidateAncestorsMeasuresWhenMoved
 		_invalidateParentWhenMovedToWindow = true;
 	}
 
-	void IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
+	bool IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
 	{
 		if (isPropagating)
 		{
 			NeedsCellLayout = true;
 		}
 
 		SetNeedsLayout();
+		return !isPropagating;
 	}
 
 	[UnconditionalSuppressMessage("Memory", "MEM0002", Justification = IUIViewLifeCycleEvents.UnconditionalSuppressMessage)]

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

@@ -306,14 +306,17 @@ public override bool Selected
 
 		protected abstract (bool, Size) NeedsContentSizeUpdate(Size currentSize);
 
-		void IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
+		bool IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
 		{
 			// 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;
+				return true;
 			}
+
+			return false;
 		}
 
 		protected void OnContentSizeChanged()

src/Controls/src/Core/Handlers/Items2/iOS/TemplatedCell2.cs

@@ -306,14 +306,17 @@ void IPlatformMeasureInvalidationController.InvalidateAncestorsMeasuresWhenMoved
 			// This is a no-op
 		}
 
-		void IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
+		bool IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
 		{
 			// 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;
+				return true;
 			}
+
+			return false;
 		}
 	}
 }

src/Controls/src/Core/Page/Page.cs

@@ -21,7 +21,7 @@ namespace Microsoft.Maui.Controls
 	/// <remarks><see cref = "Page" /> is primarily a base class for more useful derived types. Objects that are derived from the <see cref="Page"/> class are most prominently used as the top level UI element in .NET MAUI applications. In addition to their role as the main pages of applications, <see cref="Page"/> objects and their descendants can be used with navigation classes, such as <see cref="NavigationPage"/> or <see cref="FlyoutPage"/>, among others, to provide rich user experiences that conform to the expected behaviors on each platform.
 	/// </remarks>
 	[DebuggerDisplay("{GetDebuggerDisplay(), nq}")]
-	public partial class Page : VisualElement, ILayout, IPageController, IElementConfiguration<Page>, IPaddingElement, ISafeAreaView, ISafeAreaView2, IView, ITitledElement, IToolbarElement
+	public partial class Page : VisualElement, ILayout, IPageController, IElementConfiguration<Page>, IPaddingElement, ISafeAreaView, ISafeAreaView2, IView, ITitledElement, IToolbarElement, IConstrainedView
 #if IOS
 	,IiOSPageSpecifics
 #endif
@@ -212,6 +212,8 @@ public bool IgnoresContainerArea
 		/// <inheritdoc/>
 		bool ISafeAreaView.IgnoreSafeArea => !On<PlatformConfiguration.iOS>().UsingSafeArea();
 
+		bool IConstrainedView.HasFixedConstraints => true;
+
 #if IOS
 		/// <inheritdoc/>
 		bool IiOSPageSpecifics.IsHomeIndicatorAutoHidden

src/Controls/src/Core/VisualElement/VisualElement.cs

@@ -22,7 +22,7 @@ namespace Microsoft.Maui.Controls
 	/// </remarks>
 
 	[DebuggerDisplay("{GetDebuggerDisplay(), nq}")]
-	public partial class VisualElement : NavigableElement, IAnimatable, IVisualElementController, IResourcesProvider, IStyleElement, IFlowDirectionController, IPropertyPropagationController, IVisualController, IWindowController, IView, IControlsVisualElement
+	public partial class VisualElement : NavigableElement, IAnimatable, IVisualElementController, IResourcesProvider, IStyleElement, IFlowDirectionController, IPropertyPropagationController, IVisualController, IWindowController, IView, IControlsVisualElement, IConstrainedView
 	{
 		/// <summary>Bindable property for <see cref="NavigableElement.Navigation"/>.</summary>
 		public new static readonly BindableProperty NavigationProperty = NavigableElement.NavigationProperty;
@@ -978,6 +978,8 @@ internal LayoutConstraint ComputedConstraint
 
 		internal LayoutConstraint Constraint => ComputedConstraint | SelfConstraint;
 
+		bool IConstrainedView.HasFixedConstraints => Constraint == LayoutConstraint.Fixed;
+
 		/// <summary>
 		/// Gets a value that indicates that layout for this element is disabled.
 		/// </summary>

src/Core/src/Core/IConstrainedView.cs

@@ -0,0 +1,6 @@
+namespace Microsoft.Maui;
+
+internal interface IConstrainedView
+{
+	bool HasFixedConstraints { get; }
+}

src/Core/src/Handlers/Page/PageHandler.iOS.cs

@@ -21,14 +21,6 @@ protected override ContentView CreatePlatformView()
 			throw new InvalidOperationException($"PageViewController.View must be a {nameof(ContentView)}");
 		}
 
-		public override void SetVirtualView(IView view)
-		{
-			base.SetVirtualView(view);
-
-			// Ensure we tag the ContentView as a Page so that InvalidateAncestorsMeasures can stop propagation here
-			PlatformView.IsPage = true;
-		}
-
 		public static void MapBackground(IPageHandler handler, IContentView page)
 		{
 			if (handler is IPlatformViewHandler platformViewHandler && platformViewHandler.ViewController is not null)

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

@@ -16,8 +16,6 @@ public class ContentView : MauiView
 		// verify we're using the correct subview for masking (and any other purposes)
 		internal const nint ContentTag = 0x63D2A0;
 
-		internal bool IsPage { get; set; }
-
 		public ContentView()
 		{
 			if (OperatingSystem.IsIOSVersionAtLeast(13) || OperatingSystem.IsMacCatalystVersionAtLeast(13, 1))

src/Core/src/Platform/iOS/IPlatformMeasureInvalidationController.cs

@@ -3,5 +3,5 @@ namespace Microsoft.Maui.Platform;
 internal interface IPlatformMeasureInvalidationController
 {
 	void InvalidateAncestorsMeasuresWhenMovedToWindow();
-	void InvalidateMeasure(bool isPropagating = false);
+	bool InvalidateMeasure(bool isPropagating = false);
 }

src/Core/src/Platform/iOS/MauiScrollView.cs

@@ -87,10 +87,12 @@ void IPlatformMeasureInvalidationController.InvalidateAncestorsMeasuresWhenMoved
 			_invalidateParentWhenMovedToWindow = true;
 		}
 
-		void IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
+		bool IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
 		{
 			SetNeedsLayout();
 			InvalidateConstraintsCache();
+
+			return !isPropagating;
 		}
 
 		bool IsMeasureValid(double widthConstraint, double heightConstraint)

src/Core/src/Platform/iOS/MauiView.cs

@@ -24,6 +24,8 @@ public IView? View
 			set => _reference = value == null ? null : new(value);
 		}
 
+		bool HasFixedConstraints => CrossPlatformLayout is IConstrainedView { HasFixedConstraints: true };
+
 		bool RespondsToSafeArea()
 		{
 			if (_respondsToSafeArea.HasValue)
@@ -55,6 +57,11 @@ protected bool IsMeasureValid(double widthConstraint, double heightConstraint)
 			return heightConstraint == _lastMeasureHeight && widthConstraint == _lastMeasureWidth;
 		}
 
+		bool HasBeenMeasured()
+		{
+			return !double.IsNaN(_lastMeasureWidth) && !double.IsNaN(_lastMeasureHeight);
+		}
+
 		protected void InvalidateConstraintsCache()
 		{
 			_lastMeasureWidth = double.NaN;
@@ -128,10 +135,11 @@ public override void LayoutSubviews()
 			// If the SuperView is a cross-platform layout backed view (i.e. MauiView, MauiScrollView, LayoutView, ..),
 			// then measurement has already happened via SizeThatFits and doesn't need to be repeated in LayoutSubviews.
 			// This is especially important to avoid overriding potentially infinite measurement constraints
-			// imposed by the parent (i.e. scroll view) with the current bounds.
+			// imposed by the parent (i.e. scroll view) with the current bounds, except when our bounds are fixed by constraints.
 			// But we _do_ need LayoutSubviews to make a measurement pass if the parent is something else (for example,
 			// the window); there's no guarantee that SizeThatFits has been called in that case.
-			if (!IsMeasureValid(widthConstraint, heightConstraint) && !this.IsFinalMeasureHandledBySuperView())
+			if (!IsMeasureValid(widthConstraint, heightConstraint) && !this.IsFinalMeasureHandledBySuperView() ||
+			    !HasBeenMeasured() && HasFixedConstraints)
 			{
 				CrossPlatformMeasure(widthConstraint, heightConstraint);
 				CacheMeasureConstraints(widthConstraint, heightConstraint);
@@ -163,10 +171,27 @@ void IPlatformMeasureInvalidationController.InvalidateAncestorsMeasuresWhenMoved
 			_invalidateParentWhenMovedToWindow = true;
 		}
 
-		void IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
+		bool IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
 		{
 			InvalidateConstraintsCache();
 			SetNeedsLayout();
+
+			// If we're propagating, we can stop at the first view with fixed constraints
+			if (isPropagating && HasFixedConstraints)
+			{
+				// We're stopping propagation here, but we have to account for the wrapper view
+				// which needs to be invalidated for consistency too.
+				if (Superview is WrapperView wrapper)
+				{
+					wrapper.SetNeedsLayout();
+				}
+
+				return false;
+			}
+
+			// If we're not propagating, then this view is the one triggering the invalidation
+			// and one possible cause is that constraints have changed, so we have to propagate the invalidation.
+			return true;
 		}
 
 		[UnconditionalSuppressMessage("Memory", "MEM0002", Justification = IUIViewLifeCycleEvents.UnconditionalSuppressMessage)]

src/Core/src/Platform/iOS/ViewExtensions.cs

@@ -287,16 +287,21 @@ public static void InvalidateMeasure(this UIView platformView, IView view)
 
 		internal static void InvalidateMeasure(this UIView platformView)
 		{
+			var propagate = true;
+
 			if (platformView is IPlatformMeasureInvalidationController mauiPlatformView)
 			{
-				mauiPlatformView.InvalidateMeasure();
+				propagate = mauiPlatformView.InvalidateMeasure();
 			}
 			else
 			{
 				platformView.SetNeedsLayout();
 			}
 
-			platformView.InvalidateAncestorsMeasures();
+			if (propagate)
+			{
+				platformView.InvalidateAncestorsMeasures();
+			}
 		}
 
 		internal static void InvalidateAncestorsMeasures(this UIView child)
@@ -322,22 +327,20 @@ internal static void InvalidateAncestorsMeasures(this UIView child)
 				}
 
 				// Now invalidate the parent view
+				var propagate = true;
 				var superviewMauiPlatformLayout = superview as IPlatformMeasureInvalidationController;
 				if (superviewMauiPlatformLayout is not null)
 				{
-					superviewMauiPlatformLayout.InvalidateMeasure(isPropagating: true);
+					propagate = superviewMauiPlatformLayout.InvalidateMeasure(isPropagating: true);
 				}
 				else
 				{
 					superview.SetNeedsLayout();
 				}
 
-				// Potential improvement: if the MAUI view (superview here) is constrained to a fixed size, we could stop propagating
-				// when doing this, we must pay attention to a scenario where a non-fixed-size view becomes fixed-size
-				if (superview is ContentView { IsPage: true } or UIScrollView)
+				if (!propagate)
 				{
-					// We reached the root view or a scrollable area (includes collection view), stop propagating
-					// The view will eventually watch its content size and invoke InvalidateAncestorsMeasures when needed
+					// We've been asked to stop propagation, so let's stop here
 					return;
 				}
 
@@ -1013,7 +1016,8 @@ internal static float GetDisplayDensity(this UIView? view) =>
 
 		private const nint NativeViewControlledByCrossPlatformLayout = 0x63D2A1;
 
-		internal static bool IsFinalMeasureHandledBySuperView(this UIView? view) => view?.Superview is ICrossPlatformLayoutBacking { CrossPlatformLayout: not null } or { Tag: NativeViewControlledByCrossPlatformLayout };
+		internal static bool IsFinalMeasureHandledBySuperView(this UIView? view) 
+			=> view?.Superview is ICrossPlatformLayoutBacking { CrossPlatformLayout: not null } or { Tag: NativeViewControlledByCrossPlatformLayout };
 
 		internal static void MarkAsCrossPlatformLayoutBacking(this UIView view)
 		{

src/Core/src/Platform/iOS/WrapperView.cs

@@ -319,10 +319,11 @@ void IPlatformMeasureInvalidationController.InvalidateAncestorsMeasuresWhenMoved
 			_invalidateParentWhenMovedToWindow = true;
 		}
 
-		void IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
+		bool IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
 		{
 			InvalidateConstraintsCache();
 			SetNeedsLayout();
+			return true;
 		}
 
 		[UnconditionalSuppressMessage("Memory", "MEM0002", Justification = IUIViewLifeCycleEvents.UnconditionalSuppressMessage)]

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

@@ -87,6 +87,5 @@ override Microsoft.Maui.Handlers.EditorHandler.NeedsContainer.get -> bool
 override Microsoft.Maui.Handlers.WindowHandler.DisconnectHandler(UIKit.UIWindow! platformView) -> void
 *REMOVED*override Microsoft.Maui.Handlers.ScrollViewHandler.NeedsContainer.get -> bool
 override Microsoft.Maui.Handlers.ImageButtonHandler.SetupContainer() -> void
-override Microsoft.Maui.Handlers.PageHandler.SetVirtualView(Microsoft.Maui.IView! view) -> void
 *REMOVED*override Microsoft.Maui.Platform.WrapperView.SetNeedsLayout() -> void
 *REMOVED*override Microsoft.Maui.Platform.MauiView.SetNeedsLayout() -> void

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

@@ -88,6 +88,5 @@ override Microsoft.Maui.Handlers.EditorHandler.NeedsContainer.get -> bool
 override Microsoft.Maui.Handlers.WindowHandler.DisconnectHandler(UIKit.UIWindow! platformView) -> void
 *REMOVED*override Microsoft.Maui.Handlers.ScrollViewHandler.NeedsContainer.get -> bool
 override Microsoft.Maui.Handlers.ImageButtonHandler.SetupContainer() -> void
-override Microsoft.Maui.Handlers.PageHandler.SetVirtualView(Microsoft.Maui.IView! view) -> void
 *REMOVED*override Microsoft.Maui.Platform.WrapperView.SetNeedsLayout() -> void
 *REMOVED*override Microsoft.Maui.Platform.MauiView.SetNeedsLayout() -> void