Don't propagate VE.Frame changes back down to the Handler

src/Controls/src/Core/Element/Element.cs

@@ -571,7 +571,7 @@ protected override void OnPropertyChanged([CallerMemberName] string propertyName
 		{
 			base.OnPropertyChanged(propertyName);
 
-			Handler?.UpdateValue(propertyName);
+			UpdateHandlerValue(propertyName);
 
 			if (_effects?.Count > 0)
 			{
@@ -583,6 +583,9 @@ protected override void OnPropertyChanged([CallerMemberName] string propertyName
 			}
 		}
 
+		private protected virtual void UpdateHandlerValue(string property) =>
+			Handler?.UpdateValue(property);
+
 		internal IEnumerable<Element> Descendants() =>
 			Descendants<Element>();
 

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

@@ -1942,6 +1942,19 @@ static double EnsurePositive(double value)
 			return value;
 		}
 
+		private protected override void UpdateHandlerValue(string property)
+		{
+			// The HeightProperty and WidthProperty are not designed to propagate back to the handler.
+			// Instead, we use WidthRequestProperty and HeightRequestProperty to propagate changes to the handler.
+			// HeightProperty and WidthProperty are readonly and only update when the VisualElement.Frame property is set
+			// during an arrange pass, which indicates the actual width and height of the platform element.
+			// Changes to WidthRequestProperty and HeightRequestProperty will propagate to the handler via the `OnRequestChanged` method.
+			if (this.Batched && (property == HeightProperty.PropertyName || property == WidthProperty.PropertyName))
+				return;
+
+			base.UpdateHandlerValue(property);
+		}
+
 		/// <inheritdoc/>
 		double IView.Width
 		{

src/Controls/tests/Core.UnitTests/TestClasses/BasicVisualElement.cs

@@ -0,0 +1,23 @@
+using System.Threading.Tasks;
+using Microsoft.Maui.Animations;
+
+using Microsoft.Maui.Handlers;
+
+namespace Microsoft.Maui.Controls.Core.UnitTests
+{
+    public class BasicVisualElement : VisualElement
+    {
+    }
+
+    public class BasicVisualElementHandler : ViewHandler<BasicVisualElement, object>
+    {
+        public BasicVisualElementHandler(IPropertyMapper mapper, CommandMapper commandMapper = null) : base(mapper, commandMapper)
+        {
+        }
+
+        protected override object CreatePlatformView()
+        {
+            return new object();
+        }
+    }
+}

src/Controls/tests/Core.UnitTests/VisualElementTests.cs

@@ -2,7 +2,12 @@
 using System.Data.Common;
 using System.Threading.Tasks;
 using Microsoft.Maui.Controls.Shapes;
+
+using Microsoft.Maui.Controls.Hosting;
 using Microsoft.Maui.Graphics;
+using Microsoft.Maui.Hosting;
+using Microsoft.Maui.Platform;
+
 using Microsoft.Maui.Handlers;
 using Microsoft.Maui.Primitives;
 using Xunit;
@@ -237,5 +242,86 @@ public async Task ShadowDoesNotLeak()
 
 			Assert.False(reference.IsAlive, "VisualElement should not be alive!");
 		}
+
+		[Fact]
+		public void HandlerDoesntPropagateWidthChangesDuringBatchUpdates()
+		{
+			bool mapperCalled = false;
+
+			var mapper = new PropertyMapper<IView, ViewHandler>(ViewHandler.ViewMapper)
+			{
+				[nameof(IView.Height)] = (_,_) => mapperCalled = true,
+				[nameof(IView.Width)] = (_,_) => mapperCalled = true,
+			};
+
+			var mauiApp1 = MauiApp.CreateBuilder()
+				.UseMauiApp<ApplicationStub>()
+				.ConfigureMauiHandlers(handlers => handlers.AddHandler<BasicVisualElement>((services) => new BasicVisualElementHandler(mapper)))
+				.Build();
+
+			var element = new BasicVisualElement();
+			var platformView = element.ToPlatform(new MauiContext(mauiApp1.Services));
+
+			mapperCalled = false;
+			element.Frame = new Rect(0,0,100,100);
+			Assert.False(mapperCalled);
+		}
+
+		[Fact]
+		public void HandlerDoesPropagateWidthChangesWhenUpdatedDuringSizedChanged()
+		{
+			bool mapperCalled = false;
+
+			var mapper = new PropertyMapper<IView, ViewHandler>(ViewHandler.ViewMapper)
+			{
+				[nameof(IView.Height)] = (_,_) => mapperCalled = true,
+				[nameof(IView.Width)] = (_,_) => mapperCalled = true,
+			};
+
+			var mauiApp1 = MauiApp.CreateBuilder()
+				.UseMauiApp<ApplicationStub>()
+				.ConfigureMauiHandlers(handlers => handlers.AddHandler<BasicVisualElement>((services) => new BasicVisualElementHandler(mapper)))
+				.Build();
+
+			var element = new BasicVisualElement();
+			var platformView = element.ToPlatform(new MauiContext(mauiApp1.Services));
+
+			element.SizeChanged += (_,_) => element.HeightRequest = 100;
+			mapperCalled = false;
+			element.Frame = new Rect(0,0,100,100);
+
+			Assert.True(mapperCalled);
+		}
+
+		[Fact]
+		public void WidthAndHeightRequestPropagateToHandler()
+		{
+			int heightMapperCalled = 0;
+			int widthMapperCalled = 0;
+
+			var mapper = new PropertyMapper<IView, ViewHandler>(ViewHandler.ViewMapper)
+			{
+				[nameof(IView.Height)] = (_,_) => heightMapperCalled++,
+				[nameof(IView.Width)] = (_,_) => widthMapperCalled++,
+			};
+
+			var mauiApp1 = MauiApp.CreateBuilder()
+				.UseMauiApp<ApplicationStub>()
+				.ConfigureMauiHandlers(handlers => handlers.AddHandler<BasicVisualElement>((services) => new BasicVisualElementHandler(mapper)))
+				.Build();
+
+			var element = new BasicVisualElement();
+			var platformView = element.ToPlatform(new MauiContext(mauiApp1.Services));
+
+			heightMapperCalled = 0;
+			widthMapperCalled = 0;
+			element.WidthRequest = 99;
+			Assert.Equal(1, heightMapperCalled);
+			Assert.Equal(1, widthMapperCalled);
+
+			element.HeightRequest = 99;
+			Assert.Equal(2, heightMapperCalled);
+			Assert.Equal(2, widthMapperCalled);
+		}
 	}
 }