Fix for [iOS] Use non-overridden traits in AppInfoImplementation.RequestTheme

src/Controls/tests/TestCases.HostApp/Issues/Issue23411.xaml

@@ -0,0 +1,52 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue23411">
+
+  <ScrollView AutomationId="ThemePage">
+    <VerticalStackLayout
+            Padding="30,0"
+            Spacing="25">
+      <Image
+                Source="dotnet_bot.png"
+                HeightRequest="185"
+                Aspect="AspectFit"
+                SemanticProperties.Description="dot net bot in a race car number eight" />
+
+      <Label
+                Text="Hello, World!"
+                Style="{StaticResource Headline}"
+                SemanticProperties.HeadingLevel="Level1" />
+
+      <Label
+                Text="Welcome to &#10;.NET Multi-platform App UI"
+                Style="{StaticResource SubHeadline}"
+                SemanticProperties.HeadingLevel="Level2"
+                SemanticProperties.Description="Welcome to dot net Multi platform App U I" />
+
+      <Button   AutomationId="ModalPageButton"
+                x:Name="ModalPageBtn"
+                Text="Open modal page"
+                Clicked="OnModalPage"
+                HorizontalOptions="Fill" />
+
+      <Button
+                x:Name="LightThemeBtn"
+                Text="Light theme" 
+                Clicked="OnLightTheme"
+                HorizontalOptions="Fill" />
+
+      <Button
+                x:Name="DarkThemeBtn"
+                Text="Dark theme" 
+                Clicked="OnDarkTheme"
+                HorizontalOptions="Fill" />
+
+      <Button AutomationId="ResetThemeButton"
+                x:Name="ResetThemeBtn"
+                Text="Reset theme" 
+                Clicked="OnResetTheme"
+                HorizontalOptions="Fill" />
+    </VerticalStackLayout>
+  </ScrollView>
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue23411.xaml.cs

@@ -0,0 +1,43 @@
+#if IOS
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.PlatformConfiguration;
+using Microsoft.Maui.Controls.PlatformConfiguration.iOSSpecific;
+using Application = Microsoft.Maui.Controls.Application;
+using NavigationPage = Microsoft.Maui.Controls.NavigationPage;
+
+namespace Maui.Controls.Sample.Issues
+{
+	[Issue(IssueTracker.Github, 23411, "[iOS]Use non-overridden traits in AppInfoImplementation.RequestTheme",
+		PlatformAffected.iOS)]
+	public partial class Issue23411 : ContentPage
+	{
+		public Issue23411()
+		{
+			InitializeComponent();
+			Application.Current.UserAppTheme = AppTheme.Dark;
+		}
+
+		private void OnModalPage(object sender, EventArgs e)
+		{
+			var modalPage = new NavigationPage(new Issue23411() { Title = "Modal Page" ,AutomationId = "PageSheetModalPage" });
+			modalPage.On<iOS>().SetModalPresentationStyle(UIModalPresentationStyle.PageSheet);
+			Navigation.PushModalAsync(modalPage);
+		}
+
+		private void OnDarkTheme(object sender, EventArgs e)
+		{
+			Application.Current!.UserAppTheme = AppTheme.Dark;
+		}
+
+		private void OnLightTheme(object sender, EventArgs e)
+		{
+			Application.Current!.UserAppTheme = AppTheme.Light;
+		}
+
+		private void OnResetTheme(object sender, EventArgs e)
+		{
+			Application.Current!.UserAppTheme = AppTheme.Unspecified;
+		}
+	}
+}
+#endif

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue23411.cs

@@ -0,0 +1,32 @@
+#if IOS
+using NUnit.Framework.Legacy;
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+    internal class Issue23411 : _IssuesUITest
+	{
+		public override string Issue => "[iOS]Use non-overridden traits in AppInfoImplementation.RequestTheme";
+
+		public Issue23411(TestDevice device) : base(device)
+		{
+		}
+
+		[Test]
+		[Category(UITestCategories.Page)]
+		public void ThemeUnspecifiedDoesNotAffectModalPageSheet()
+		{
+			// Is a iOS issue; see https://github.com/dotnet/maui/issues/23411
+			App.WaitForElement("ThemePage");
+			App.WaitForElement("ModalPageButton");
+		    App.Tap("ModalPage");
+			App.WaitForElement("PageSheetModalPage");
+			App.WaitForElement("ResetThemeButton");
+			VerifyScreenshot();
+
+		}
+	}
+}
+#endif

src/Essentials/src/AppInfo/AppInfo.ios.tvos.watchos.macos.cs

@@ -54,9 +54,9 @@ public AppTheme RequestedTheme
 				if ((OperatingSystem.IsIOS() && !OperatingSystem.IsIOSVersionAtLeast(13, 0)) || (OperatingSystem.IsTvOS() && !OperatingSystem.IsTvOSVersionAtLeast(13, 0)))
 					return AppTheme.Unspecified;
 
-				var traits =
-					MainThread.InvokeOnMainThread(() => WindowStateManager.Default.GetCurrentUIViewController()?.TraitCollection) ??
-					UITraitCollection.CurrentTraitCollection;
+			    // This always returns the non-overridden trais which allows restoring the
+				// application back to the system theme.
+				var traits = UIScreen.MainScreen.TraitCollection;
 
 				var uiStyle = traits.UserInterfaceStyle;