[Settings]Takes some time to adapt to theme change

[jaimecbernardo]

Microsoft PowerToys version

0.71.0-pre

Installation method

Dev build in Visual Studio

Running as admin

None

Area(s) with issue?

Settings

Steps to reproduce

After #25936 , when changing the windows theme with the Settings page opened, it takes a bit to adapt to the theme change.

1. Open the Settings window and make sure that its theme is set to use the system's theme.
2. Change the theme in Settings. (Either light or dark mode, the one you're not currently using.

✔️ Expected Behavior

The Settings window reacts to the theme change.

❌ Actual Behavior

The Settings window won't react to the theme change unless you use its UI for a bit.

Other Software

Tested on Windows 11 only, but I assume Windows 10 might have issues too.

[Jay-o-Way]

I notice that only the General page triggers the switch, so...
@niels9001 Cause: the following code is only in GeneralPage.xaml.cs

PowerToys/src/settings-ui/Settings.UI/SettingsXAML/Views/GeneralPage.xaml.cs

Lines 92 to 115 in 187f0e3

	public static int UpdateUIThemeMethod(string themeName)
	{
	switch (themeName?.ToUpperInvariant())
	{
	case "LIGHT":
	// OobeShellPage.OobeShellHandler.RequestedTheme = ElementTheme.Light;
	ShellPage.ShellHandler.RequestedTheme = ElementTheme.Light;
	break;
	case "DARK":
	// OobeShellPage.OobeShellHandler.RequestedTheme = ElementTheme.Dark;
	ShellPage.ShellHandler.RequestedTheme = ElementTheme.Dark;
	break;
	case "SYSTEM":
	// OobeShellPage.OobeShellHandler.RequestedTheme = ElementTheme.Default;
	ShellPage.ShellHandler.RequestedTheme = ElementTheme.Default;
	break;
	default:
	Logger.LogError($"Unexpected theme name: {themeName}");
	break;
	}
	App.HandleThemeChange();
	return 0;
	}

This code must be "app-scope"

[Jay-o-Way]

@niels9001 it really is best practice to leave absolutely as much as possible to the framework/SDK. In other words: remove as much "manual" code as possible.

[niels9001]

@niels9001 it really is best practice to leave absolutely as much as possible to the framework/SDK. In other words: remove as much "manual" code as possible.

It should work by default.. but theme changing at runtime has been a pain point for a long, long time. The theming stuff we are doing turned out to be a spaghetti - and we are making registry edits to make things work. It's not the way, yet there isn't a great one :-).

Let's leave it at prio3 though - it only happens on theme change within the app which is not a common thing and navigating to a different page solves it.

[Jay-o-Way]

It should work by default

And it does - if only we stop making so much spaghetti! (I don't even like spaghetti)

...yet there isn't a great one :-).

There is - like I said: Let the framework/sdk/winui/whateverthenameis do its thing. #LessIsMore!

@niels9001 I am literally showing you what/where the problem is. Why can't you accept that?

[niels9001]

It should work by default

And it does - if only we stop making so much spaghetti! (I don't even like spaghetti)

...yet there isn't a great one :-).

There is - like I said: Let the framework/sdk/winui/whateverthenameis do its thing. #LessIsMore!

As far as I am aware, there's is no out-of-the-box way to set the ApplicationTheme outside of the constructor of App.xaml.cs. This means that changing the entire app window theme at runtime is not (fully) supported within the app - only when triggered by W11 Settings (this dates back to the Windows 8 days where this wasn't added - see microsoft/microsoft-ui-xaml#4474).
The only thing we can update is the theme of the root UI element (e.g. the page that sits within the Window). But things like Mica, titlebar (caption buttons), control specific acrylic effects (e.g. flyout backgrounds) are controlled by the Window. That's why we need to do a bunch of custom code (call it hacky if you will 😁) to make it (somewhat) work. (See also microsoft/microsoft-ui-xaml#8249)

So.. it's not an easy thing that we somehow decided to make more complicated 😊.

@niels9001 I am literally showing you what/where the problem is.

I think the code you mentioned gets triggered whenever the ViewModel on the General page gets/sets the theme (e.g. on page load or when the user selects the theme option).. That's the reason why navigating from and back to the General page triggers that method and applies the correct theme.
What we need is to catch the OS trigger that the theme changes and then apply the theme logic. We try to do that with the theme listener:

PowerToys/src/settings-ui/Settings.UI/SettingsXAML/App.xaml.cs

Line 294 in 187f0e3

themeListener = new ThemeListener();

.
If I recall correctly, I think that works but we get the wrong theme passed - not sure though.. I know I struggled a lot to get #25936 in a workable state due to this (although I'm pretty sure I tested this scenario as well so this is surprising to see).

If you have any code suggestions on how to fix this, please let it be known in this thread! (Or feel free to PR the solution 😁)

Why can't you accept that?

In my earlier comment, I tried to explain what's the root cause of why these theme related bugs pop-up across various WinUI3 modules. Not sure how that is "not accepting" things? I just mentioned that this is not a 'medium' bug but a Prio3 as @jaimecbernardo tagged it to be (it's not a common scenario an average user would run into nor is it a blocking/crashing bug). I just wanted to point out that there's a more complex root issue causing this and that this is not a straight-forward thing to fix - hopefully my explanation in this comment is more clear, but it takes a lot of time to write these things down.

Point of note: at times you come off as lecturing people on why things/code aren't the way they should be, or making snarky remarks. Yeah, people and the code they write ain't perfect (definitely this codebase isn't :-)). I'm sure you don't mean it that way, but please take that in mind and check out our Code of Conduct. We are all friends here!

[stefansjfw]

The work associated with this issue has been released as part of the 0.76 sprint. Please update PowerToys to the latest. https://github.com/microsoft/PowerToys/releases