Knowledge sharing for theme switching

[Spiritreader]

Hey @namazso!

Again thank you for your contribution of the CThemeManager interface in C# that you gave us (the Auto Dark Mode project).

Microsoft has very quietly announced that they will incorporate the support of switching themes in PowerToys. albeit a very basic version, it can only toggle between light and dark modes.

Since UxTheme version 4.0 you mentioned that ADM now works with the provided IThemeManager2 interface.

We were still having issues where the Window theme was not applied correctly and incorporated a couple of workarounds to improve the theme switching experience.
Now: In Microsoft's annoucement, they also updated the PowerToys code to reveal what they are doing such that the window theme synchronization works.

They are broadcasting two messages to all windows.

SendMessageTimeout(HWND_BROADCAST, WM_SETTINGCHANGE, 0, reinterpret_cast<LPARAM>(L"ImmersiveColorSet"), SMTO_ABORTIFHUNG, 5000, nullptr);
SendMessageTimeout(HWND_BROADCAST, WM_THEMECHANGED, 0, 0, SMTO_ABORTIFHUNG, 5000, nullptr);

HWND_BROADCAST = 0xffff;
WM_SETTINGCHANGE = 0x001A;
WM_THEMECHANGED = 0x031A;
SMTO_ABORTIFHUNG = 0x0002;

In my limited testing, that resolved all glitches that came with applying (custom) themes.
Maybe this info is useful information for you as well, so I thought I'd share.

Cheers!
Sam from the ADM team

[namazso]

Interesting! Well, it's not useful to SecureUxTheme anymore since it does no theme switching whatsoever, but it could be incorporated into ThemeToolSharp.