fix(reg): Workaround Gallery measure issue on Android

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml/Given_UIElement.cs

@@ -938,7 +938,11 @@ namespace Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml
 
 			using var _ = new AssertionScope();
 
+#if __ANDROID__
+			ctl1.MeasureCount.Should().Be(2);
+#else
 			ctl1.MeasureCount.Should().Be(1);
+#endif
 			ctl2.MeasureCount.Should().Be(2);
 			ctl3.MeasureCount.Should().Be(1);
 

src/Uno.UI/Extensions/ViewExtensions.Android.cs

@@ -21,6 +21,7 @@ using System.Threading.Tasks;
 using Android.Views.Animations;
 using Microsoft.UI.Xaml.Controls;
 using Uno.UI.Controls;
+using Microsoft.UI.Xaml.Media;
 
 namespace Uno.UI
 {
@@ -705,6 +706,10 @@ namespace Uno.UI
 				{
 					root = parent;
 				}
+				else if (root is DependencyObject @do && VisualTreeHelper.GetParent(@do) is ViewGroup managedParent)
+				{
+					root = managedParent;
+				}
 				else
 				{
 					break;

src/Uno.UI/UI/Xaml/ILayouterElement.cs

@@ -74,6 +74,7 @@ internal static class LayouterElementExtensions
 			if (isDirty || frameworkElement is null)
 			{
 				// We must reset the flag **BEFORE** doing the actual measure, so the elements are able to re-invalidate themselves
+				// TODO: We are not controlling measure dirty path on Android. If we did in future, we must clear it here as well.
 				frameworkElement?.ClearLayoutFlags(UIElement.LayoutFlag.MeasureDirty);
 
 				// The dirty flag is explicitly set on this element
@@ -91,7 +92,9 @@ internal static class LayouterElementExtensions
 					LayoutInformation.SetAvailableSize(element, availableSize);
 				}
 
-				return true; // end of isDirty processing
+				// TODO: This is NOT correct.
+				// We shouldn't return here. Skipping children measure is incorrect but fixing it on Android isn't trivial.
+				return true;
 			}
 
 			// The measure dirty flag is set on one of the descendents:
@@ -110,6 +113,8 @@ internal static class LayouterElementExtensions
 				{
 					var previousDesiredSize = childAsUIElement.m_desiredSize;
 					childAsUIElement.EnsureLayoutStorage();
+
+					// TODO: This is NOT correct. This should call DoMeasure (the same method we are in currently!)
 					element.Layouter.MeasureChild(child, childAsUIElement.m_previousAvailableSize);
 					var newDesiredSize = childAsUIElement.m_desiredSize;
 					if (newDesiredSize != previousDesiredSize)

src/Uno.UI/UI/Xaml/Media/VisualTreeHelper.cs

@@ -393,6 +393,31 @@ namespace Microsoft.UI.Xaml.Media
 		{
 #if __ANDROID__
 			view.AddView(child);
+
+			// Reset to original (invalidated) state
+			child.ResetLayoutFlags();
+			if (view.IsMeasureDirtyPathDisabled)
+			{
+				FrameworkElementHelper.SetUseMeasurePathDisabled(child); // will invalidate too
+			}
+			else
+			{
+				child.InvalidateMeasure();
+			}
+
+			if (view.IsArrangeDirtyPathDisabled)
+			{
+				FrameworkElementHelper.SetUseArrangePathDisabled(child); // will invalidate too
+			}
+			else
+			{
+				child.InvalidateArrange();
+			}
+
+			// Force a new measure of this element (the parent of the new child)
+			view.InvalidateMeasure();
+			view.InvalidateArrange();
+
 #elif __IOS__ || __MACOS__
 			view.AddSubview(child);
 #elif __CROSSRUNTIME__

src/Uno.UI/UI/Xaml/UIElement.cs

@@ -1149,6 +1149,9 @@ namespace Microsoft.UI.Xaml
 			// Use a non-virtual version of the RequestLayout method, for performance.
 			base.RequestLayout();
 			SetLayoutFlags(LayoutFlag.MeasureDirty);
+
+			// HACK: Android's implementation of measure/arrange is not accurate. See comments in LayouterElementExtensions.DoMeasure
+			(VisualTreeHelper.GetParent(this) as UIElement)?.InvalidateMeasure();
 #elif __IOS__
 			SetNeedsLayout();
 			SetLayoutFlags(LayoutFlag.MeasureDirty);