[iOS/macCatalyst] Fix Entry and Editor BackgroundColor reset when set to null (#34741)

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### Issue Details
On iOS and macCatalyst, setting BackgroundColor = null on an Entry or
Editor at runtime does not restore the native default appearance. Once a
custom color is applied, it persists even after the property is cleared.

### Root Cause
The shared iOS background update logic only resets BackgroundColor =
null for LayoutView subclasses — all other UIView types silently return.
MauiTextField (Entry) and MauiTextView (Editor) are not LayoutView
subclasses, so the reset is skipped.

### Description of Change
Platform-specific MapBackground methods were added to
EntryHandler.iOS.cs and EditorHandler.iOS.cs. When
Background.IsNullOrEmpty(), they now explicitly set
platformView.BackgroundColor = null to restore native appearance.
 
Validated the behavior in the following platforms
 
- [x] Android
- [x] Windows
- [x] iOS
- [x] Mac
 
### Issues Fixed
  
Fixes #34611   

### Output  ScreenShot

|Before|After|
|--|--|
| <video
src="https://github.com/user-attachments/assets/5ca30c6d-c069-4c04-989b-4dae36584cb4"
>| <video
src="https://github.com/user-attachments/assets/ee9e2a2e-c210-47cc-9f85-2526780d398b">|

---------

Co-authored-by: Jakub Florkowski <42434498+kubaflo@users.noreply.github.com>

Author: 2 people

src/Controls/tests/TestCases.Android.Tests/snapshots/android/EntryAndEditorBackgroundColorShouldResetToDefaultWhenSetToNull.png

@@ -0,0 +1,69 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 34611, "Entry and Editor BackgroundColor not reset to Null", PlatformAffected.iOS | PlatformAffected.macOS)]
+public class Issue34611 : TestContentPage
+{
+	Entry _entry;
+	Editor _editor;
+
+	protected override void Init()
+	{
+		Title = "Issue34611";
+
+		_entry = new Entry
+		{
+			AutomationId = "TestEntry",
+			Text = "Entry background should reset",
+			Placeholder = "Entry"
+		};
+
+		_editor = new Editor
+		{
+			AutomationId = "TestEditor",
+			Text = "Editor background should reset",
+			HeightRequest = 120,
+			Placeholder = "Editor"
+		};
+
+		var applyButton = new Button
+		{
+			AutomationId = "ApplyBackgroundColorButton",
+			Text = "Apply BackgroundColor"
+		};
+
+		applyButton.Clicked += (_, _) =>
+		{
+			_entry.BackgroundColor = Colors.Red;
+			_editor.BackgroundColor = Colors.LightBlue;
+		};
+
+		var resetButton = new Button
+		{
+			AutomationId = "ResetToDefaultButton",
+			Text = "Reset to Default"
+		};
+
+		resetButton.Clicked += (_, _) =>
+		{
+			_entry.BackgroundColor = null;
+			_editor.BackgroundColor = null;
+		};
+
+		Content = new VerticalStackLayout
+		{
+			Margin = new Thickness(20, 0, 20, 0),
+			Spacing = 12,
+			Children =
+			{
+				new Label
+				{
+					Text = "Apply custom backgrounds, then reset them to null."
+				},
+				_entry,
+				_editor,
+				applyButton,
+				resetButton
+			}
+		};
+	}
+}

src/Controls/tests/TestCases.HostApp/Issues/Issue34611.cs

@@ -0,0 +1,25 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue34611 : _IssuesUITest
+{
+	public Issue34611(TestDevice device) : base(device)
+	{
+	}
+
+	public override string Issue => "Entry and Editor BackgroundColor not reset to Null";
+
+	[Test]
+	[Category(UITestCategories.Entry)]
+	public void EntryAndEditorBackgroundColorShouldResetToDefaultWhenSetToNull()
+	{
+		App.WaitForElement("ApplyBackgroundColorButton");
+		App.Tap("ApplyBackgroundColorButton");
+		App.WaitForElement("TestEntry");
+		App.Tap("ResetToDefaultButton");
+		VerifyScreenshot();
+	}
+}

src/Controls/tests/TestCases.Mac.Tests/snapshots/mac/EntryAndEditorBackgroundColorShouldResetToDefaultWhenSetToNull.png

@@ -84,6 +84,28 @@ public static void MapText(IEditorHandler handler, IEditor editor)
 			MapFormatting(handler, editor);
 		}
 
+		public static void MapBackground(IEditorHandler handler, IEditor editor)
+		{
+			if (handler.PlatformView is not MauiTextView platformView)
+				return;
+
+			if (editor.Background is ImageSourcePaint image)
+			{
+				var provider = handler.GetRequiredService<IImageSourceServiceProvider>();
+				platformView.UpdateBackgroundImageSourceAsync(image.ImageSource, provider)
+					.FireAndForget(handler);
+			}
+			else if (editor.Background.IsNullOrEmpty())
+			{
+				platformView.RemoveBackgroundLayer();
+				platformView.BackgroundColor = null;
+			}
+			else
+			{
+				platformView.UpdateBackground(editor);
+			}
+		}
+
 		public static void MapTextColor(IEditorHandler handler, IEditor editor) =>
 			handler.PlatformView?.UpdateTextColor(editor);
 

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34611.cs

@@ -48,6 +48,30 @@ public static void MapText(IEntryHandler handler, IEntry entry)
 			MapFormatting(handler, entry);
 		}
 
+		public static void MapBackground(IEntryHandler handler, IEntry entry)
+		{
+			if (handler.PlatformView is not MauiTextField platformView)
+				return;
+
+			if (entry.Background is ImageSourcePaint image)
+			{
+				var provider = handler.GetRequiredService<IImageSourceServiceProvider>();
+				platformView.UpdateBackgroundImageSourceAsync(image.ImageSource, provider)
+					.FireAndForget(handler);
+				return;
+			}
+			else if (entry.Background.IsNullOrEmpty())
+			{
+				platformView.RemoveBackgroundLayer();
+				platformView.BackgroundColor = null;
+				return;
+			}
+			else
+			{
+				platformView.UpdateBackground(entry);
+			}
+		}
+
 		public static void MapTextColor(IEntryHandler handler, IEntry entry)
 		{
 			handler.PlatformView?.UpdateTextColor(entry);
@@ -212,8 +236,8 @@ void OnEditingChanged(object? sender, EventArgs e)
 
 					VirtualView.UpdateText(platformView.Text);
 				}
-			}	
-				
+			}
+
 			void OnEditingEnded(object? sender, EventArgs e)
 			{
 				if (sender is MauiTextField platformView && VirtualView is IEntry virtualView)

src/Controls/tests/TestCases.WinUI.Tests/snapshots/windows/EntryAndEditorBackgroundColorShouldResetToDefaultWhenSetToNull.png

@@ -5,4 +5,6 @@ override Microsoft.Maui.Handlers.StepperHandler.GetDesiredSize(double widthConst
 override Microsoft.Maui.Platform.MauiTextView.TextAlignment.get -> UIKit.UITextAlignment
 override Microsoft.Maui.Platform.MauiTextView.TextAlignment.set -> void
 override Microsoft.Maui.Platform.MauiView.DidUpdateFocus(UIKit.UIFocusUpdateContext! context, UIKit.UIFocusAnimationCoordinator! coordinator) -> void
+static Microsoft.Maui.Handlers.EditorHandler.MapBackground(Microsoft.Maui.Handlers.IEditorHandler! handler, Microsoft.Maui.IEditor! editor) -> void
+static Microsoft.Maui.Handlers.EntryHandler.MapBackground(Microsoft.Maui.Handlers.IEntryHandler! handler, Microsoft.Maui.IEntry! entry) -> void
 static Microsoft.Maui.Handlers.DatePickerHandler.MapFlowDirection(Microsoft.Maui.Handlers.IDatePickerHandler! handler, Microsoft.Maui.IDatePicker! datePicker) -> void