Microsoft KB Archive/140723

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HOWTO: Force a Screen Saver to Close Once Started in Windows NT

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Q140723

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The information in this article applies to:


 * Microsoft Win32 Software Development Kit (SDK), used with:
 * Microsoft Windows NT Server versions 3.1, 3.5, 3.51, 4.0
 * Microsoft Windows NT Workstation versions 3.1, 3.5, 3.51, 4.0
 * the operating system: Microsoft Windows 2000

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

  PostMessage (GetActiveWindow, WM_CLOSE, 0, 0L); Windows NT, however, introduces the concept of separate desktops, so that applications can run on one, and screen savers can run on another. This makes screen saver termination under Windows NT and Windows 2000 a bit more difficult.

MORE INFORMATION
Obtaining a handle to the currently active screen saver window under Windows NT or Windows 2000 is not as straightforward as it is in Windows 3.1 and Windows 95. Calling GetForegroundWindow returns NULL because the screen saver is running on a different desktop than the calling application. Similarly, calling FindWindow ("WindowsScreenSaverClass", NULL) to determine if the screen saver is currently active does not work either.

To do this, 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 terminates the screen saver application.

  BOOL CALLBACK KillScreenSaverFunc(HWND hwnd, LPARAM lParam) {     if(IsWindowVisible(hwnd)) 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); } Note that terminating a screen saver that is already running as demonstrated above is totally separate from disabling the screen saver altogether, so that no screen saver starts after the designated time period expires. This can be done easily using:

  SystemParametersInfo( SPI_SETSCREENSAVEACTIVE,

FALSE, 0,                        SPIF_SENDWININICHANGE ); This method works well for terminating the currently running screen saver. However, one problem that you might encounter is that the system will not restart the screen saver unless the user moves the mouse or presses a key. If you need the screen saver to start up again, you'll need to reinitialize the time-out period. Do this by:


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

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 * Using SetCursorPos to simulate user input.

Both of these methods will cause the system to restart the time-out counter for the screen saver.

Additional query words: deactivate disable stop running turn off screensaver

Keywords : _IK kbOSWinNT kbOSWinNT310 kbOSWinNT350 kbOSWinNT351 kbOSWinNT400 kbOSWin2000 kbScreenSaver kbSDKWin32 kbGrpDSUser

Issue type : kbhowto

Technology : kbWin32SDKSearch kbAudDeveloper kbSDKSearch kbWin32sSearch