[iOS] Application cannot be reset back to system theme

[filipnavara]

Description

The accessor AppInfo.RequestedTheme returns an overridden theme once it's in effect and modal sheet is displayed:

https://github.com/dotnet/maui/blob/main/src/Essentials/src/AppInfo/AppInfo.ios.tvos.watchos.macos.cs#L58

It's used by Application class to set the value of PlatformAppTheme:

https://github.com/dotnet/maui/blob/main/src/Controls/src/Core/Application/Application.cs#L505

Once the theme is overridden once by setting Application.UserAppTheme to Light or Dark, the value of AppInfo.RequestedTheme sticks to the overridden trait for the current page (may be eventually reset on next page navigation due to how trait change events are propagated). This causes PlatformAppTheme to reflect the overridden value instead of the platform one, and setting Application.UserAppTheme = AppTheme.Unspecified no longer resets to the current OS default.

Steps to Reproduce

1. [Have the iOS in Dark mode]
2. Set Application.UserAppTheme = AppTheme.Light on startup
3. Open modal sheet
4. Set Application.UserAppTheme = AppTheme.Unspecifed on user action; observe no effect

With the repro project:

• Set iOS to Dark mode
• Run the project - the app starts as Light
• Click "Open modal page"
• Click "Reset theme"
• Observe the theme doesn't change

Note that the repro app changes the theme just fine from the main page, it's broken only when the modal page is shown. Only then AppInfo.RequestedTheme start returning the overridden value that is wrongly propagated to Application.PlatformAppTheme.

Link to public reproduction project repository

https://github.com/filipnavara/maui-dark-mode-ios-bug

Version with bug

8.0.61 SR6.1

Is this a regression from previous behavior?

Not sure, did not test other versions

Last version that worked well

Unknown/Other

Affected platforms

iOS

Affected platform versions

iOS 17.5

Did you find any workaround?

No response

Relevant log output

No response

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• If you change the theme after running the app, it will not be applied normally. (#6876), similarity score: 0.77

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[filipnavara]

Seems like UIScreen.MainScreen.TraitCollection always returns the non-overridden trait.

Current workaround:

	class AppInfoService : IAppInfo
	{
		private IAppInfo innerAppInfo;

		public AppInfoService()
		{
			innerAppInfo = (IAppInfo)Activator.CreateInstance(Type.GetType("Microsoft.Maui.ApplicationModel.AppInfoImplementation, Microsoft.Maui.Essentials"));
		}        

		public string PackageName => innerAppInfo.PackageName;

		public string Name => innerAppInfo.Name;

		public string VersionString => innerAppInfo.VersionString;

		public Version Version => innerAppInfo.Version;

		public string BuildString => innerAppInfo.BuildString;

		public AppTheme RequestedTheme
		{
			get
			{
				if ((OperatingSystem.IsIOS() && !OperatingSystem.IsIOSVersionAtLeast(13, 0)) || (OperatingSystem.IsTvOS() && !OperatingSystem.IsTvOSVersionAtLeast(13, 0)))
					return AppTheme.Unspecified;

				var traits = UIScreen.MainScreen.TraitCollection;
				var uiStyle = traits.UserInterfaceStyle;

				return uiStyle switch
				{
					UIUserInterfaceStyle.Light => AppTheme.Light,
					UIUserInterfaceStyle.Dark => AppTheme.Dark,
					_ => AppTheme.Unspecified
				};                
			}            
		}

		public AppPackagingModel PackagingModel => innerAppInfo.PackagingModel;

		public LayoutDirection RequestedLayoutDirection => innerAppInfo.RequestedLayoutDirection;

		public void ShowSettingsUI() => innerAppInfo.ShowSettingsUI();
	}

			typeof(AppInfo).GetMethod("SetCurrent", BindingFlags.NonPublic | BindingFlags.Static, new[] { typeof(IAppInfo) }).Invoke(
				null, new[] { new AppInfoService() });

[ninachen03]

I can repro this issue at iOS platform on the latest 17.11.0 Preview 2.1(8.0.61 &8.0.60)

[filipnavara]

I can repro this issue at Android platform on the latest 17.11.0 Preview 2.1(8.0.61 &8.0.60)

I'm not sure if it has the same root cause then... this bug is specific to iOS. I'll check Android later on.

[ninachen03]

My typo. I reproduced it on iOS. I updated my comment. Sorry for the inconvenience.

[miko1258]

We can reproduce it on our iOS app as well

[Alex-Dobrynin]

When this will be fixed? the Application object does not react to system theme changes