Fix iOS ScrollView content being measured with non-infinite constraints during LayoutSubviews pass

Author: albyrock87

src/Controls/tests/TestCases.HostApp/Issues/Issue27169.cs

@@ -0,0 +1,21 @@
+namespace Controls.TestCases.HostApp.Issues;
+
+[Issue(IssueTracker.Github, 27169, "Grid inside ScrollView should measure with infinite constraints", PlatformAffected.iOS)]
+public class Issue27169 : ContentPage
+{
+	public Issue27169()
+	{
+		var grid = new Grid { VerticalOptions = LayoutOptions.Start };
+		grid.RowDefinitions.Add(new RowDefinition(GridLength.Star));
+		grid.RowDefinitions.Add(new RowDefinition(GridLength.Star));
+		var firstContent = new Label { MinimumHeightRequest = 200, AutomationId = "StubLabel", BackgroundColor = Colors.LightBlue };
+		firstContent.SetBinding(Label.TextProperty, new Binding(nameof(Label.Height), source: firstContent));
+		var secondContent = new Label { MinimumHeightRequest = 40, Text = "Second Content", BackgroundColor = Colors.SlateBlue };
+		
+		grid.Add(firstContent);
+		grid.Add(secondContent, 0 , 1);
+
+		var scrollView = new ScrollView { Content = grid };
+		Content = scrollView;
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue27169.cs

@@ -0,0 +1,20 @@
+using NUnit.Framework;
+using NUnit.Framework.Legacy;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+	public class Issue27169(TestDevice device) : _IssuesUITest(device)
+	{
+		public override string Issue => "Grid inside ScrollView should measure with infinite constraints";
+
+		[Test]
+		[Category(UITestCategories.ScrollView)]
+		public void ScrollViewContentLayoutMeasuresWithInfiniteConstraints()
+		{
+			var measuredHeight = App.WaitForElement("StubLabel").GetText()!;
+			ClassicAssert.AreEqual("200", measuredHeight);
+		}
+	}
+}

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

@@ -36,11 +36,13 @@ public override void LayoutSubviews()
 				_lastArrangeWidth = widthConstraint;
 				_lastArrangeHeight = heightConstraint;
 
-				// If the SuperView is a MauiView (backing a cross-platform ContentView or Layout), then measurement
-				// has already happened via SizeThatFits and doesn't need to be repeated in LayoutSubviews. But we
-				// _do_ need LayoutSubviews to make a measurement pass if the parent is something else (for example,
+				// If the SuperView is a MauiView or MauiScrollView (backing a cross-platform ContentView or Layout), 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.
+				// 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) && Superview is not MauiView)
+				if (!IsMeasureValid(widthConstraint, heightConstraint) && Superview is not (MauiView or MauiScrollView))
 				{
 					crossPlatformLayout.CrossPlatformMeasure(widthConstraint, heightConstraint);
 					CacheMeasureConstraints(widthConstraint, heightConstraint);

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

@@ -125,12 +125,13 @@ public override void LayoutSubviews()
 			var widthConstraint = bounds.Width;
 			var heightConstraint = bounds.Height;
 
-			// If the SuperView is a MauiView (backing a cross-platform ContentView or Layout), then measurement
-			// has already happened via SizeThatFits and doesn't need to be repeated in LayoutSubviews. But we
-			// _do_ need LayoutSubviews to make a measurement pass if the parent is something else (for example,
+			// If the SuperView is a MauiView or MauiScrollView (backing a cross-platform ContentView or Layout), 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.
+			// 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) && Superview is not MauiView)
+			if (!IsMeasureValid(widthConstraint, heightConstraint) && Superview is not (MauiView or MauiScrollView))
 			{
 				CrossPlatformMeasure(widthConstraint, heightConstraint);
 				CacheMeasureConstraints(widthConstraint, heightConstraint);