[iOS] Fix issue rendering Button Background gradient with shadow

src/Controls/samples/Controls.Sample/Pages/Controls/ButtonPage.xaml

@@ -57,6 +57,26 @@
                         </LinearGradientBrush>
                     </Button.Background>
                 </Button>
+                <Label
+                    Text="Shadow"
+                    Style="{StaticResource Headline}" />
+                <Button 
+                    x:Name="ShadowButton"
+                    Text="Shadow"
+                    HorizontalOptions="Center">
+                    <Button.Background>
+                        <LinearGradientBrush EndPoint="1,0">
+                            <GradientStop Color="Yellow"
+                                          Offset="0.1" />
+                            <GradientStop Color="Green"
+                                          Offset="1.0" />
+                        </LinearGradientBrush>
+                    </Button.Background>
+                    <Button.Shadow>
+                        <Shadow
+                            Brush="Green" />
+                    </Button.Shadow>
+                </Button>
                 <Label
                     Text="TextColor"
                     Style="{StaticResource Headline}"/>

src/Core/src/Handlers/View/ViewHandler.iOS.cs

@@ -55,7 +55,9 @@ internal static void MapContextFlyout(IElementHandler handler, IContextFlyoutEle
 		static partial void MappingFrame(IViewHandler handler, IView view)
 		{
 			UpdateTransformation(handler, view);
-			handler.ToPlatform().UpdateBackgroundLayerFrame();
+
+			if (view.Background is not null)
+				handler.ToPlatform().UpdateBackgroundLayerFrame();
 		}
 
 		public static void MapTranslationX(IViewHandler handler, IView view)

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

@@ -268,23 +268,43 @@ public static void UpdateBackgroundLayerFrame(this UIView view)
 
 			var layer = view.Layer;
 
-			UpdateBackgroundLayerFrame(layer, view.Bounds);
+			UpdateBackgroundLayerFrame(layer, view.Bounds, view is WrapperView);
 		}
 
-		static void UpdateBackgroundLayerFrame(CALayer layer, CGRect bounds)
+		static void UpdateBackgroundLayerFrame(CALayer layer, CGRect bounds, bool getAllSubLayers)
 		{
 			if (layer == null || layer.Sublayers == null || layer.Sublayers.Length == 0)
 				return;
 
-			foreach (var sublayer in layer.Sublayers)
+			IEnumerable<CALayer> subLayers = getAllSubLayers ? layer.GetLayers() : layer.Sublayers;
+
+			foreach (var sublayer in subLayers)
 			{
 				if (sublayer.Name == BackgroundLayerName && sublayer.Frame != bounds)
 				{
 					sublayer.Frame = bounds;
 					break;
 				}
 
-				UpdateBackgroundLayerFrame(sublayer, bounds);
+				UpdateBackgroundLayerFrame(sublayer, bounds, getAllSubLayers);
+			}
+		}
+
+		static IEnumerable<CALayer> GetLayers(this CALayer root)
+		{
+			var stack = new Stack<CALayer>();
+			stack.Push(root);
+
+			while (stack.Count > 0)
+			{
+				var current = stack.Pop();
+				yield return current;
+
+				if (current.Sublayers is not null)
+				{
+					foreach (var child in current.Sublayers)
+						stack.Push(child);
+				}
 			}
 		}
 

src/Core/tests/DeviceTests/Handlers/Button/ButtonHandlerTests.iOS.cs

@@ -57,6 +57,42 @@ public async Task ValidateDefaultAccessibilityTraits()
 			Assert.Equal(UIAccessibilityTrait.Button, trait);
 		}
 
+		[Theory]
+		[InlineData(null)]
+		[InlineData("#FF0000")]
+		[InlineData("#00FF00")]
+		[InlineData("#0000FF")]
+		[InlineData("#000000")]
+		public async Task BackgroundWithShadowRenderCorrectly(string colorHex)
+		{
+			var expectedColor = Color.FromArgb(colorHex);
+
+			var button = new ButtonStub
+			{
+				Text = "Test",
+				Background = new SolidPaintStub(expectedColor),
+				Shadow = new ShadowStub
+				{
+					Paint = new SolidPaintStub(Colors.Black),
+					Offset = new Point(10, 10),
+					Opacity = 1.0f,
+					Radius = 2.0f
+				}
+			};
+
+			var handler = await CreateHandlerAsync(button);
+
+			await InvokeOnMainThreadAsync(async () =>
+			{
+				await handler.PlatformView.AttachAndRun(async () =>
+				{
+					handler.UpdateValue(nameof(IButton.Background));
+
+					await handler.PlatformView.AssertContainsColor(expectedColor);
+				});
+			});
+		}
+
 		bool ImageSourceLoaded(ButtonHandler buttonHandler) =>
 			buttonHandler.PlatformView.ImageView.Image != null;