How to Force a ScreenSaver to Close Once Started in Windows NT

• Microsoft Win32 Application Programming Interface (API) included with Microsoft Windows NT versions 3.1, 3.5, 3.51

SUMMARY

Sometimes applications need to terminate a screensaver that is already running. In Windows 3.1 or Windows 95, a screensaver could be terminated easily by posting a WM_CLOSE message to the currently active screensaver window as in this example:

    PostMessage (GetActiveWindow(), WM_CLOSE, 0, 0L);

MORE INFORMATION

Under Windows NT, obtaining a handle to the currently active screensaver window is not as straightforward as it is in Windows 3.1 and Windows 95. Calling GetForegroundWindow() returns NULL because the screensaver is running on a different desktop than the calling application. Similarly, calling FindWindow ("WindowsScreenSaverClass", NULL) to determine if the screen saver is currently active won't work either.

The way to do it is to get a handle to the screen saver's desktop, enumerate that desktop's windows, and then post a WM_CLOSE to the screen saver window.

The following code demonstrates how to do this. Note that if a screen saver password is set, the following code brings up the password dialog box, prompts the user for a password, and then actually terminating the screen saver application.

   BOOL CALLBACK KillScreenSaverFunc(HWND hwnd, LPARAM lParam)
   {
      PostMessage(hwnd, WM_CLOSE, 0, 0);
      return TRUE;
   }

   HDESK hdesk;

   hdesk = OpenDesktop(TEXT("Screen-saver"),
                       0,
                       FALSE,
                       DESKTOP_READOBJECTS | DESKTOP_WRITEOBJECTS);
   if (hdesk)
   {
      EnumDesktopWindows(hdesk, KillScreenSaverFunc, 0);
      CloseDesktop(hdesk);
   }

   SystemParametersInfo( SPI_SETSCREENSAVEACTIVE,
                         FALSE,
                         0,
                         SPIF_SENDWININICHANGE
                       );

• Calling SystemParametersInfo( SPI_SETSCREENSAVEACTIVE, TRUE, 0, SPIF_SENDWININICHANGE).

  -or-

• Using SetCursorPos() to simulate user input.