Notification/subscription method for Windows 10 theme change

Question

As yolu may have noticed, MS introduced a modern kind of 'theming' in Windows 10 regarding the basic OS elements like start menu and taskbar. With newer versions, you can choose a 'light' theme as an alternative to the default black theme.

I was wondering if there is an API or hook to elegantly and (more importantly) efficiently check live for theme changes (Did not find anything in the MS docs regarding this, but often enough these gems are pretty hidden there IMHO).

Specific problem: When you have a desktop application with a system tray icon, chances are high that you designed it to be bright. Nearly all of the modern Windows icons feature such a style (simple and white, yielding good readability on the black taskbar). Now you can provide a different version in a darker style for the light theme, but how to notice when to apply this on the fly?

I'm aware of the registry key under HCU (Software/Microsoft/Windows/CurrentVersion/Themes/Personalize) which is what I'm utilizing right now. However, blindly checking for change every x milliseconds seems pretty awkward.

If no such thing is available, I'm also happy to hear some ideas for more efficient implementations of such a check.

Related: [How to detect Windows 10 light/dark mode in Win32 application?](https://stackoverflow.com/q/51334674/7571258) — zett42, Sep 02 '19 at 11:27
WinRT class `UISettings` exposes the [`ColorValuesChanged`](https://learn.microsoft.com/en-us/uwp/api/windows.ui.viewmanagement.uisettings.colorvalueschanged) event. Starting from [this answer](https://stackoverflow.com/a/55670413/7571258), I was able to quickly hack together a C++/WinRT console app that subscribes to that event. I leave it to make that an actual answer to people who are more knowledgable in C++/WinRT. — zett42, Sep 02 '19 at 12:02
Possible duplicate of [How to detect Windows 10 light/dark mode in Win32 application?](https://stackoverflow.com/questions/51334674/how-to-detect-windows-10-light-dark-mode-in-win32-application) — Christian.K, Sep 03 '19 at 05:19
@Christian.K Not really IMHO, albeit there are some overlappings. It has to be distinguished between the app theme (UWP framework/APIs) and the system theme - I‘ll go for the hint from Strive Sun ATM — dfuchs, Sep 03 '19 at 07:10

Strive Sun · Accepted Answer · 2019-09-03T02:32:39.517

6

Method 1： Use RegNotifyChangeKeyValue

Notifies the caller about changes to the attributes or contents of a specified registry key.

Methon 2: Use WM_SETTINGCHANGE

Applications should send WM_SETTINGCHANGE to all top-level windows when they make changes to system parameters. (This message cannot be sent directly to a window.) To send the WM_SETTINGCHANGE message to all top-level windows, use the SendMessageTimeout function with the hwnd parameter set to HWND_BROADCAST.

I tend to use the second method, I have tried, and have been able to work successfully.

Minimum code example：

case WM_SETTINGCHANGE:
    {
        if (!lstrcmp(LPCTSTR(lParam), L"ImmersiveColorSet"))
        {
            //theme has been changed
        }
    }

edited Sep 03 '19 at 02:32

answered Sep 02 '19 at 10:08

Strive Sun

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Unless explicitly noted otherwise, the registry is not a public programming interface. – IInspectable Sep 02 '19 at 10:30
@IInspectable thx, I suggest OP use the second method to detect theme changes. – Strive Sun Sep 03 '19 at 02:44
@Strive Sun MSFT Thanks for the hint! Totally forgot about RegNotifyChangeKeyValue, but never knew about WM_SETTINGCHANGE. The second approach looks very promising for this – dfuchs Sep 03 '19 at 07:12
1

@StriveSun-MSFT Where did you find "ImmersiveColorSet" in Microsoft's documentation? Neither Google nor I are finding it on anything referenced by WM_SETTINGCHANGE, except answers like these. I'm happy to have found an answer, but I would like to know it is documented and likely to remain reliable. – Steve Valliere May 08 '20 at 15:53
This message doesn't get emitted when I try it in Python by registering a window subclass – demberto May 10 '22 at 06:36
The message doesn't get emitted when I override the WNDPROC either – demberto May 27 '22 at 14:58
@SteveValliere It is not recommended that you use this method in a production environment. – Strive Sun Jun 27 '22 at 04:46
@demberto Maybe you can open a new case to ask, my program just for the windows desktop platform. – Strive Sun Jun 27 '22 at 04:48
@StriveSun The programming language used to create an application doesn't change the messages sent to a window. – demberto Jun 27 '22 at 04:58
@demberto **The message doesn't get emitted** , do you mean "WM_SETTINGCHANGE"? – Strive Sun Jun 27 '22 at 06:15
@StriveSun Yes ofcourse, that's what your answer says – demberto Jun 27 '22 at 07:18
@demberto Show me your code sample. – Strive Sun Jun 27 '22 at 07:31

Notification/subscription method for Windows 10 theme change

1 Answers1