Receive screensaver notification

I want to receive a notification in my C++ application when a screensaver is about to start. I tried listening to WM_SYSCOMMAND messages with wParam == SC_SCREENSAVE which some people think should do the trick. Tha开发者_JAVA百科t didn't work. Spy++ even showed that my window didn't receive any WM_SYSCOMMAND message. Interesting thing is when I turned off the monitor I did receive the message with wParam == SC_MONITORPOWER. Am I understanding it wrong? Or did I just miss something?

Edit: For testing I used the default windows screensaver (the one with windows logo).

It appears that I will receive the SC_SCREENSAVE message only when my window has focus. The way around this is to set global hook. That would require me to put the callback function in a separate DLL and there is also this scary message about hooks slowing down the system so I decided to drop the idea of responding to screensaver start.

This is a relatively complex task (although it would be nice if it were easy).

Some of these tests you'll find online only work if your window is in focus. If it's running in the background it may not receive such messages.

Other tests rely on a screensaver program running (check the currently set screensaver, and then watch the process list to see if it's active) but don't work if you go into powersave mode, or if your screensaver is a black screen (ie, no program, just monitor off).

I don't believe there's an ideal way to do this. You might want to go back to the beginning and think more carefully about why you need to detect this state, and what you are trying to accomplish. You might need a different solution.

Probably my answer comes too late.

The MSDN handles screensavers under "Legacy". On a notebook they waste battery and on a PC they are also useless. It is better to turn the monitor off than letting it show a screensaver.

As you don't explain exactly what you want to do I don't know if you really need the notification BEFORE the saver starts or if it is enough to get notified when it already has just started.

In the latter case it is easy. Write a thread that periodically checks:

    BOOL b_SaverRunning;
    SystemParametersInfo(SPI_GETSCREENSAVERRUNNING, 0, &b_SaverRunning, 0);