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Fix iOS ScrollView content being measured with non-infinite constraints during LayoutSubviews pass (#27298)
* Fix iOS ScrollView content being measured with non-infinite constraints during LayoutSubviews pass * - add interface to WrapperView and move to ext method --------- Co-authored-by: Shane Neuville <[email protected]>
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+69
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‎src/Controls/tests/TestCases.HostApp/Issues/Issue27169.cs

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

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

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

‎src/Core/src/Handlers/ScrollView/ScrollViewHandler.iOS.cs

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@@ -24,7 +24,7 @@ protected override void ConnectHandler(UIScrollView platformView)
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{
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base.ConnectHandler(platformView);
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if (platformView is MauiScrollView platformScrollView)
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if (platformView is ICrossPlatformLayoutBacking platformScrollView)
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{
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platformScrollView.CrossPlatformLayout = this;
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}
@@ -34,7 +34,7 @@ protected override void ConnectHandler(UIScrollView platformView)
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protected override void DisconnectHandler(UIScrollView platformView)
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{
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if (platformView is MauiScrollView platformScrollView)
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if (platformView is ICrossPlatformLayoutBacking platformScrollView)
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{
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platformScrollView.CrossPlatformLayout = null;
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}

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

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@@ -6,7 +6,7 @@
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namespace Microsoft.Maui.Platform
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{
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public class MauiScrollView : UIScrollView, IUIViewLifeCycleEvents
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public class MauiScrollView : UIScrollView, IUIViewLifeCycleEvents, ICrossPlatformLayoutBacking
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{
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bool _invalidateParentWhenMovedToWindow;
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double _lastMeasureHeight;
@@ -16,12 +16,14 @@ public class MauiScrollView : UIScrollView, IUIViewLifeCycleEvents
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WeakReference<ICrossPlatformLayout>? _crossPlatformLayoutReference;
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internal ICrossPlatformLayout? CrossPlatformLayout
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ICrossPlatformLayout? ICrossPlatformLayoutBacking.CrossPlatformLayout
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{
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get => _crossPlatformLayoutReference != null && _crossPlatformLayoutReference.TryGetTarget(out var v) ? v : null;
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set => _crossPlatformLayoutReference = value == null ? null : new WeakReference<ICrossPlatformLayout>(value);
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}
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internal ICrossPlatformLayout? CrossPlatformLayout => ((ICrossPlatformLayoutBacking)this).CrossPlatformLayout;
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public override void LayoutSubviews()
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{
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// LayoutSubviews is invoked while scrolling, so we need to arrange the content only when it's necessary.
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_lastArrangeWidth = widthConstraint;
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_lastArrangeHeight = heightConstraint;
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// If the SuperView is a MauiView (backing a cross-platform ContentView or Layout), then measurement
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// has already happened via SizeThatFits and doesn't need to be repeated in LayoutSubviews. But we
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// _do_ need LayoutSubviews to make a measurement pass if the parent is something else (for example,
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// If the SuperView is a cross-platform layout backed view (i.e. MauiView, MauiScrollView, LayoutView, ..),
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// then measurement has already happened via SizeThatFits and doesn't need to be repeated in LayoutSubviews.
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// This is especially important to avoid overriding potentially infinite measurement constraints
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// imposed by the parent (i.e. scroll view) with the current bounds.
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// But we _do_ need LayoutSubviews to make a measurement pass if the parent is something else (for example,
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// the window); there's no guarantee that SizeThatFits has been called in that case.
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if (!IsMeasureValid(widthConstraint, heightConstraint) && Superview is not MauiView)
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if (!IsMeasureValid(widthConstraint, heightConstraint) && !this.IsFinalMeasureHandledBySuperView())
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{
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crossPlatformLayout.CrossPlatformMeasure(widthConstraint, heightConstraint);
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CacheMeasureConstraints(widthConstraint, heightConstraint);

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

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@@ -125,12 +125,13 @@ public override void LayoutSubviews()
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var widthConstraint = bounds.Width;
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var heightConstraint = bounds.Height;
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// If the SuperView is a MauiView (backing a cross-platform ContentView or Layout), then measurement
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// has already happened via SizeThatFits and doesn't need to be repeated in LayoutSubviews. But we
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// _do_ need LayoutSubviews to make a measurement pass if the parent is something else (for example,
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// If the SuperView is a cross-platform layout backed view (i.e. MauiView, MauiScrollView, LayoutView, ..),
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// then measurement has already happened via SizeThatFits and doesn't need to be repeated in LayoutSubviews.
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// This is especially important to avoid overriding potentially infinite measurement constraints
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// imposed by the parent (i.e. scroll view) with the current bounds.
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// But we _do_ need LayoutSubviews to make a measurement pass if the parent is something else (for example,
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// the window); there's no guarantee that SizeThatFits has been called in that case.
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if (!IsMeasureValid(widthConstraint, heightConstraint) && Superview is not MauiView)
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if (!IsMeasureValid(widthConstraint, heightConstraint) && !this.IsFinalMeasureHandledBySuperView())
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{
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CrossPlatformMeasure(widthConstraint, heightConstraint);
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CacheMeasureConstraints(widthConstraint, heightConstraint);

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

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@@ -945,5 +945,7 @@ internal static float GetDisplayDensity(this UIView? view) =>
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internal static bool ShowSoftInput(this UIView inputView) => inputView.BecomeFirstResponder();
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internal static bool IsSoftInputShowing(this UIView inputView) => inputView.IsFirstResponder;
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internal static bool IsFinalMeasureHandledBySuperView(this UIView? view) => view?.Superview is ICrossPlatformLayoutBacking { CrossPlatformLayout: not null };
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}
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}

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

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@@ -9,16 +9,22 @@
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namespace Microsoft.Maui.Platform
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{
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public partial class WrapperView : UIView, IDisposable, IUIViewLifeCycleEvents
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public partial class WrapperView : UIView, IDisposable, IUIViewLifeCycleEvents, ICrossPlatformLayoutBacking
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{
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bool _fireSetNeedsLayoutOnParentWhenWindowAttached;
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WeakReference<ICrossPlatformLayout>? _crossPlatformLayoutReference;
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internal ICrossPlatformLayout? CrossPlatformLayout
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ICrossPlatformLayout? ICrossPlatformLayoutBacking.CrossPlatformLayout
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{
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get => _crossPlatformLayoutReference != null && _crossPlatformLayoutReference.TryGetTarget(out var v) ? v : null;
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set => _crossPlatformLayoutReference = value == null ? null : new WeakReference<ICrossPlatformLayout>(value);
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}
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internal ICrossPlatformLayout? CrossPlatformLayout
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{
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get => ((ICrossPlatformLayoutBacking)this).CrossPlatformLayout;
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set => ((ICrossPlatformLayoutBacking)this).CrossPlatformLayout = value;
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}
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double _lastMeasureHeight = double.NaN;
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double _lastMeasureWidth = double.NaN;

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