HOWTO: Know When Your Screen Saver Starts

• Microsoft Windows versions 95, 98
• Microsoft Windows NT 4.0
• Microsoft Windows 2000

SUMMARY

A screen saver will start, pending your choices, whenever there is no mouse or keyboard activity for the current screen saver timeout period. Some applications need to know when the screen saver has started in order to do some background processing, for example, writing or updating the data to disk.

MORE INFORMATION

When a screen saver starts, it posts a WM_SYSCOMMAND message to the foreground window with WPARAM as SC_SCREENSAVE. To detect and notify other applications of this event, use the following steps:

1. Install WH_GETMESSAGE Global hook.

      
      hHook = SetWindowsHookEx(WH_GETMESSAGE, (HOOKPROC)HookProc,
              (HINSTANCE) hMod, 0); 




2. Define a user-defined registered message for example, "ScreenSaverStarted".

   
      UINT WM_SCRNSVSTART = RegisterWindowMessage("ScreenSaverStarted"); 




3. Broadcast this message to all top-level windows in the system.

   
      LRESULT CALLBACK   HookProc(UINT code , WPARAM wParam, LPARAM lParam)
      {
   	MSG *msg = (MSG *)lParam;
   	if ( msg->message == WM_SYSCOMMAND && 
   msg->wParam == SC_SCREENSAVE)
   	{	// broadcast message to all top-level windows
   		// Or execute some other code here
   		PostMessage(HWND_BROADCAST, WM_SCRNSVSTART, 0, 0);
   	} 
   		// Always call next hook in chain 
   	return CallNextHookEx(hHook, code,  wParam, lParam);
      } 




4. Uninstall the hook.

   
     UnhookWindowsHookEx(hHook); 

   On Windows 98 and Windows 2000, you can query the system by calling SystemParametersInfo with uiAction as SPI_GETSCREENSAVERRUNNING.

   
      BOOL bActive;  
      SystemParametersInfo(SPI_GETSCREENSAVERRUNNING, NULL,(LPVOID) &bActive, NULL); 
      //bActive will be true if Screen Saver is running 

REFERENCES

For additional information, please click the article number(s) below to view the article(s) in the Microsoft Knowledge Base:

Q140723 HOWTO: Force a Screen Saver to Close Once Started in Windows NT

Q150785 HOWTO: Detect If a Screen Saver Is Running on Windows NT

© Microsoft Corporation 1999, All Rights Reserved.
Contributions by Gagandeep Singh, Microsoft Corporation

Additional query words:

Keywords : kbHook kbNTOS400 kbWinOS2000 kbWinOS95 kbWinOS98 kbDSupport kbhowto
Version : WINDOWS:95,98; winnt:4.0
Platform : WINDOWS winnt
Issue type : kbhowto