Fix tests

src/Core/src/CommandMapper.cs

@@ -26,16 +26,16 @@ private protected virtual void SetPropertyCore(string key, Command action)
 
 		private protected virtual void InvokeCore(string key, IElementHandler viewHandler, IElement virtualView, object? args)
 		{
-			var action = GetCommandCore(key);
+			var action = GetCommand(key);
 			action?.Invoke(viewHandler, virtualView, args);
 		}
 
-		private protected virtual Command? GetCommandCore(string key)
+		public virtual Command? GetCommand(string key)
 		{
 			if (_mapper.TryGetValue(key, out var action))
 				return action;
 			else if (Chained is not null)
-				return Chained.GetCommandCore(key);
+				return Chained.GetCommand(key);
 			else
 				return null;
 		}
@@ -75,7 +75,7 @@ public CommandMapper(CommandMapper chained)
 		{
 			get
 			{
-				var action = GetCommandCore(key) ?? throw new IndexOutOfRangeException($"Unable to find mapping for '{nameof(key)}'.");
+				var action = GetCommand(key) ?? throw new IndexOutOfRangeException($"Unable to find mapping for '{nameof(key)}'.");
 				return new Action<TViewHandler, TVirtualView, object?>((h, v, o) => action.Invoke(h, v, o));
 			}
 			set => Add(key, value);

src/Core/src/CommandMapperExtensions.cs

@@ -0,0 +1,67 @@
+using System;
+
+namespace Microsoft.Maui
+{
+	public static class CommandMapperExtensions
+	{
+		/// <summary>
+		/// Modify a command mapping in place.
+		/// </summary>
+		/// <typeparam name="TVirtualView">The cross-platform type.</typeparam>
+		/// <typeparam name="TViewHandler">The handler type.</typeparam>
+		/// <param name="commandMapper">The command mapper in which to change the mapping.</param>
+		/// <param name="key">The name of the command.</param>
+		/// <param name="method">The modified method to call when the command is updated.</param>
+		public static void ModifyMapping<TVirtualView, TViewHandler>(this CommandMapper<TVirtualView, TViewHandler> commandMapper,
+			string key, Action<TViewHandler, TVirtualView, object?, Action<IElementHandler, IElement, object?>?> method)
+			where TVirtualView : IElement where TViewHandler : IElementHandler
+		{
+			var previousMethod = commandMapper.GetCommand(key);
+
+			commandMapper.Add(key, newMethod);
+
+			void newMethod(TViewHandler handler, TVirtualView view, object? args)
+			{
+				method(handler, view, args, previousMethod);
+			}
+		}
+
+		/// <summary>
+		/// Specify a method to be run after an existing command mapping.
+		/// </summary>
+		/// <typeparam name="TVirtualView">The cross-platform type.</typeparam>
+		/// <typeparam name="TViewHandler">The handler type.</typeparam>
+		/// <param name="commandMapper">The command mapper in which to change the mapping.</param>
+		/// <param name="key">The name of the command.</param>
+		/// <param name="method">The method to call after the existing mapping is finished.</param>
+		public static void AppendToMapping<TVirtualView, TViewHandler>(this CommandMapper<TVirtualView, TViewHandler> commandMapper,
+			string key, Action<TViewHandler, TVirtualView, object?> method)
+			where TVirtualView : IElement where TViewHandler : IElementHandler
+		{
+			commandMapper.ModifyMapping(key, (handler, view, args, action) =>
+			{
+				action?.Invoke(handler, view, args);
+				method(handler, view, args);
+			});
+		}
+
+		/// <summary>
+		/// Specify a method to be run before an existing command mapping.
+		/// </summary>
+		/// <typeparam name="TVirtualView">The cross-platform type.</typeparam>
+		/// <typeparam name="TViewHandler">The handler type.</typeparam>
+		/// <param name="commandMapper">The command mapper in which to change the mapping.</param>
+		/// <param name="key">The name of the command.</param>
+		/// <param name="method">The method to call before the existing mapping begins.</param>
+		public static void PrependToMapping<TVirtualView, TViewHandler>(this CommandMapper<TVirtualView, TViewHandler> commandMapper,
+			string key, Action<TViewHandler, TVirtualView, object?> method)
+			where TVirtualView : IElement where TViewHandler : IElementHandler
+		{
+			commandMapper.ModifyMapping(key, (handler, view, args, action) =>
+			{
+				method(handler, view, args);
+				action?.Invoke(handler, view, args);
+			});
+		}
+	}
+}

src/Core/tests/DeviceTests/Handlers/View/ViewHandlerTests.Android.cs

@@ -1,10 +1,10 @@
 using Microsoft.Maui.Handlers;
+using Android.Views;
+using Android.Widget;
 
 namespace Microsoft.Maui.DeviceTests
 {
 	public partial class ViewHandlerTests
 	{
-		protected static Thing CreateNativeView() =>
-
 	}
 }

src/Core/tests/DeviceTests/Handlers/View/ViewHandlerTests.Windows.cs

@@ -1,4 +1,6 @@
 using Microsoft.Maui.Handlers;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
 
 namespace Microsoft.Maui.DeviceTests
 {

src/Core/tests/DeviceTests/Handlers/View/ViewHandlerTests.cs

@@ -1,37 +1,35 @@
 using System.Threading.Tasks;
 using Microsoft.Maui.DeviceTests.Stubs;
 using Microsoft.Maui.Handlers;
+using Microsoft.Maui.Hosting;
+using Microsoft.Maui;
 using Xunit;
 
 namespace Microsoft.Maui.DeviceTests
 {
 	[Category(TestCategory.View)]
-	public partial class ViewHandlerTests : HandlerTestBase<StubBase, StubBaseHandler>
+	public partial class ViewHandlerTests : HandlerTestBase<StubBaseHandler, StubBase>
 	{
 		[Fact(DisplayName = "NativeArrange triggers MapFrame")]
-		public Task NativeArrangeTriggersMapFrame()
+		public async Task NativeArrangeTriggersMapFrame()
 		{
-			var commandMapperField = typeof(ElementHandler).GetField("_commandMapper");
+			var didUpdateFrame = 0;
 
 			var view = new StubBase();
 
-			return InvokeOnMainThreadAsync(() =>
+			await InvokeOnMainThreadAsync(() =>
 			{
-				var handler = new StubBaseHandler(CreateNativeView());
+				var handler = new StubBaseHandler();
 
-				var viewHandler = handler as ViewHandler;
-				var commandMapper = commandMapperField.GetValue(handler) as CommandMapper;
-
-
-
-				handler.Com
+				handler.CommandMapper.AppendToMapping(nameof(IView.Frame), (h, v, a) =>
+				{
+					didUpdateFrame++;
+				});
 
 				InitializeViewHandler(view, handler);
-
-				var handler = CreateHandler(view);
-
-
 			});
+
+			Assert.Equal(1, didUpdateFrame);
 		}
 	}
 }

src/Core/tests/DeviceTests/Handlers/View/ViewHandlerTests.iOS.cs

@@ -1,4 +1,5 @@
 using Microsoft.Maui.Handlers;
+using UIKit;
 
 namespace Microsoft.Maui.DeviceTests
 {

src/Core/tests/DeviceTests/Stubs/StubBaseHandler.cs

@@ -1,10 +1,5 @@
 #nullable enable
-using System;
-using System.Collections.Generic;
-using System.Runtime.CompilerServices;
-using Microsoft.Maui.Graphics;
 using Microsoft.Maui.Handlers;
-using Microsoft.Maui.Primitives;
 
 #if __IOS__ || MACCATALYST
 using NativeView = UIKit.UIView;
@@ -18,26 +13,50 @@
 
 namespace Microsoft.Maui.DeviceTests.Stubs
 {
-	public class StubBaseHandler : ViewHandler<StubBase, NativeView>
+	public class StubBaseHandler : ViewHandler<StubBase, StubNativeView>
 	{
-		readonly NativeView _nativeView;
+		public static IPropertyMapper<StubBase, StubBaseHandler> StubMapper =
+			new PropertyMapper<StubBase, StubBaseHandler>(ViewMapper)
+			{
+			};
 
+		public static CommandMapper<StubBase, StubBaseHandler> StubCommandMapper =
+			new(ViewCommandMapper)
+			{
+			};
 
-		public static IPropertyMapper<StubBase, StubBaseHandler> StubMapper = new PropertyMapper<StubBase, StubBaseHandler>(ViewMapper)
+		public StubBaseHandler()
+			: this(null, null)
 		{
-		};
+		}
 
-		public static CommandMapper<StubBase, StubBaseHandler> StubCommandMapper = new(ViewCommandMapper)
+		public StubBaseHandler(IPropertyMapper? mapper = null, CommandMapper? commandMapper = null)
+			: base(
+				new PropertyMapper<StubBase, StubBaseHandler>(mapper ?? StubMapper),
+				new CommandMapper<StubBase, StubBaseHandler>(commandMapper ?? ViewCommandMapper))
 		{
-		};
+		}
+
+		public CommandMapper<StubBase, StubBaseHandler>? CommandMapper =>
+			_commandMapper as CommandMapper<StubBase, StubBaseHandler>;
+
+		public PropertyMapper<StubBase, StubBaseHandler>? PropertyMapper =>
+			_mapper as PropertyMapper<StubBase, StubBaseHandler>;
 
-		protected StubBaseHandler(NativeView nativeView, IPropertyMapper? mapper = null, CommandMapper? commandMapper = null)
-			: base(mapper ?? StubMapper, commandMapper ?? ViewCommandMapper)
+		protected override StubNativeView CreateNativeView() =>
+			new StubNativeView(MauiContext!);
+	}
+
+	public class StubNativeView : NativeView
+	{
+		public StubNativeView(IMauiContext mauiContext)
+#if __ANDROID__
+			: base(mauiContext.Context)
+#endif
 		{
-			_nativeView = nativeView;
+			MauiContext = mauiContext;
 		}
 
-		protected override NativeView CreateNativeView() =>
-			_nativeView;
+		public IMauiContext MauiContext { get; }
 	}
 }