BarBackground with Brush in NavigationPage on theme change

src/Controls/src/Core/Compatibility/Handlers/NavigationPage/iOS/NavigationRenderer.cs

@@ -36,6 +36,8 @@ public class NavigationRenderer : UINavigationController, INavigationViewHandler
 		bool _hasNavigationBar;
 		UIImage _defaultNavBarShadowImage;
 		UIImage _defaultNavBarBackImage;
+		Brush _currentBarBackgroundBrush;
+		Color _currentBarBackgroundColor;
 		bool _disposed;
 		IMauiContext _mauiContext;
 		IMauiContext MauiContext => _mauiContext;
@@ -262,6 +264,12 @@ protected override void Dispose(bool disposing)
 				_secondaryToolbar.RemoveFromSuperview();
 				_secondaryToolbar.Dispose();
 				_secondaryToolbar = null;
+
+				if(_currentBarBackgroundBrush is GradientBrush gb)
+					gb.InvalidateGradientBrushRequested -= OnBarBackgroundChanged;
+
+				_currentBarBackgroundBrush = null;
+				_currentBarBackgroundColor = null;
 
 				_parentFlyoutPage = null;
 				Current = null; // unhooks events
@@ -712,22 +720,44 @@ void UpdateBackgroundColor()
 			View.BackgroundColor = color;
 		}
 
+		void OnBarBackgroundChanged(object sender, EventArgs e)
+		{
+			RefreshBarBackground();
+		}
+
 		void UpdateBarBackground()
 		{
-			var barBackgroundColor = NavPage.BarBackgroundColor;
-			var barBackgroundBrush = NavPage.BarBackground;
+			if(_currentBarBackgroundBrush is GradientBrush oldGradientBrush)
+			{
+				oldGradientBrush.Parent = null;
+				oldGradientBrush.InvalidateGradientBrushRequested -= OnBarBackgroundChanged;
+			}
 
-			// if the brush has a solid color, treat it as a Color so we can compute the alpha value
-			if (NavPage.BarBackground is SolidColorBrush scb)
+			_currentBarBackgroundColor = NavPage.BarBackgroundColor;
+			_currentBarBackgroundBrush = NavPage.BarBackground;
+
+			if (_currentBarBackgroundBrush is GradientBrush newGradientBrush)
 			{
-				barBackgroundColor = scb.Color;
-				barBackgroundBrush = null;
+				newGradientBrush.Parent = NavPage;
+				newGradientBrush.InvalidateGradientBrushRequested += OnBarBackgroundChanged;
 			}
 
+			RefreshBarBackground();
+		}
+
+		void RefreshBarBackground()
+		{
+			// if the brush has a solid color, treat it as a Color so we can compute the alpha value
+			if (_currentBarBackgroundBrush is SolidColorBrush newSolidColorBrush)
+			{
+				_currentBarBackgroundColor = newSolidColorBrush.Color;
+				_currentBarBackgroundBrush = null;
+			}
+
 			if (OperatingSystem.IsIOSVersionAtLeast(13) || OperatingSystem.IsMacCatalystVersionAtLeast(13))
 			{
 				var navigationBarAppearance = NavigationBar.StandardAppearance;
-				if (barBackgroundColor is null)
+				if (_currentBarBackgroundColor is null)
 				{
 					navigationBarAppearance.ConfigureWithOpaqueBackground();
 					navigationBarAppearance.BackgroundColor = Maui.Platform.ColorExtensions.BackgroundColor;
@@ -737,17 +767,17 @@ void UpdateBarBackground()
 				}
 				else
 				{
-					if (barBackgroundColor?.Alpha < 1f)
+					if(_currentBarBackgroundColor?.Alpha < 1f)
 						navigationBarAppearance.ConfigureWithTransparentBackground();
 					else
 						navigationBarAppearance.ConfigureWithOpaqueBackground();
 
-					navigationBarAppearance.BackgroundColor = barBackgroundColor.ToPlatform();
+					navigationBarAppearance.BackgroundColor = _currentBarBackgroundColor.ToPlatform();
 				}
 
-				if (barBackgroundBrush is not null)
+				if (_currentBarBackgroundBrush is not null)
 				{
-					var backgroundImage = NavigationBar.GetBackgroundImage(barBackgroundBrush);
+					var backgroundImage = NavigationBar.GetBackgroundImage(_currentBarBackgroundBrush);
 
 					navigationBarAppearance.BackgroundImage = backgroundImage;
 				}
@@ -758,18 +788,18 @@ void UpdateBarBackground()
 			}
 			else
 			{
-				if (barBackgroundColor?.Alpha == 0f)
+				if(_currentBarBackgroundColor?.Alpha == 0f)
 				{
 					NavigationBar.SetTransparentNavigationBar();
 				}
 				else
 				{
 					// Set navigation bar background color
-					NavigationBar.BarTintColor = barBackgroundColor == null
+					NavigationBar.BarTintColor = _currentBarBackgroundColor == null
 						? UINavigationBar.Appearance.BarTintColor
-						: barBackgroundColor.ToPlatform();
+						: _currentBarBackgroundColor.ToPlatform();
 
-					var backgroundImage = NavigationBar.GetBackgroundImage(barBackgroundBrush);
+					var backgroundImage = NavigationBar.GetBackgroundImage(_currentBarBackgroundBrush);
 					NavigationBar.SetBackgroundImage(backgroundImage, UIBarMetrics.Default);
 				}
 			}

src/Controls/src/Core/Toolbar/Toolbar.Android.cs

@@ -19,6 +19,8 @@ public partial class Toolbar
 		List<IMenuItem> _currentMenuItems = new List<IMenuItem>();
 		List<ToolbarItem> _currentToolbarItems = new List<ToolbarItem>();
 
+		Brush _currentBarBackground;
+
 		NavigationRootManager? NavigationRootManager =>
 			Handler?.MauiContext?.GetNavigationRootManager();
 
@@ -103,6 +105,35 @@ void UpdateTitleView()
 			_platformTitleView.Child = (IPlatformViewHandler?)_platformTitleViewHandler;
 		}
 
+		void UpdateBarBackground()
+		{
+			if(_currentBarBackground is GradientBrush oldBarBackground)
+			{
+				oldBarBackground.Parent = null;
+				oldBarBackground.InvalidateGradientBrushRequested -= OnBarBackgroundChanged;
+			}
+
+			_currentBarBackground = BarBackground;
+
+			if(_currentBarBackground is GradientBrush newBarBackground && Parent is Element parent)
+			{
+				newBarBackground.Parent = parent;
+				newBarBackground.InvalidateGradientBrushRequested += OnBarBackgroundChanged;
+			}
+
+			RefreshBarBackground();
+		}
+
+		void OnBarBackgroundChanged(object? sender, EventArgs e)
+		{
+			RefreshBarBackground();
+		}
+
+		void RefreshBarBackground()
+		{
+			PlatformView.UpdateBarBackground(this);
+		}
+
 		public static void MapBarTextColor(ToolbarHandler arg1, Toolbar arg2) =>
 			MapBarTextColor((IToolbarHandler)arg1, arg2);
 
@@ -143,7 +174,7 @@ public static void MapBarTextColor(IToolbarHandler arg1, Toolbar arg2)
 
 		public static void MapBarBackground(IToolbarHandler arg1, Toolbar arg2)
 		{
-			arg1.PlatformView.UpdateBarBackground(arg2);
+			arg2.UpdateBarBackground();
 		}
 
 		public static void MapBackButtonTitle(IToolbarHandler arg1, Toolbar arg2)

src/Controls/tests/TestCases.HostApp/Issues/Issue24428.xaml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<NavigationPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue24428NavPage">
+	<NavigationPage.BarBackground>
+		<LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
+			<GradientStop Color="{AppThemeBinding Light=Red, Dark=Brown}" Offset="0.0" />
+			<GradientStop Color="{AppThemeBinding Light=Green, Dark=Yellow}" Offset="0.5" />
+			<GradientStop Color="{AppThemeBinding Light=Red, Dark=Brown}" Offset="1.0" />
+		</LinearGradientBrush>
+	</NavigationPage.BarBackground>
+</NavigationPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue24428.xaml.cs

@@ -0,0 +1,39 @@
+namespace Maui.Controls.Sample.Issues
+{
+	[XamlCompilation(XamlCompilationOptions.Compile)]
+	[Issue(IssueTracker.Github, 24428, "AppThemeBinding BarBackground with GradientBrush in NavigationPage not working", PlatformAffected.All)]
+	public partial class Issue24428NavPage : NavigationPage
+	{
+		public Issue24428NavPage() : base(new Issue24428ContentPage())
+		{
+			InitializeComponent();
+		}
+	}
+
+	public class Issue24428ContentPage : ContentPage
+	{
+		public Issue24428ContentPage()
+		{
+			var label1 = new Label()
+			{
+				AutomationId = "lightThemeLabel",
+				Text = "Light theme"
+			};
+
+			var label2 = new Label()
+			{
+				AutomationId = "darkThemeLabel",
+				Text = "Dark theme"
+			};
+
+			label1.SetAppTheme(IsVisibleProperty, true, false);
+			label2.SetAppTheme(IsVisibleProperty, false, true);
+
+			Content = new VerticalStackLayout()
+			{
+				label1,
+				label2
+			};
+		}
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue24428.cs

@@ -0,0 +1,35 @@
+#if ANDROID || IOS
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+	public class Issue24428NavPage : _IssuesUITest
+	{
+		public Issue24428NavPage(TestDevice testDevice) : base(testDevice)
+		{
+		}
+
+		public override string Issue => "AppThemeBinding BarBackground with GradientBrush in NavigationPage not working";
+
+		[Test]
+		[Category(UITestCategories.Page)]
+		public void NavigationBarBackgroundShouldChange()
+		{
+			try 
+			{
+				App.WaitForElement("lightThemeLabel");
+				VerifyScreenshot("NavigationBarBackgroundShouldChangeLightTheme");
+				App.SetDarkTheme();
+				App.WaitForElement("darkThemeLabel");
+				VerifyScreenshot("NavigationBarBackgroundShouldChangeDarkTheme");
+			}
+			finally
+			{
+				App.SetLightTheme();
+			}
+		}
+	}
+}
+#endif