Microsoft KB Archive/238882

HOWTO: Know When Your Screen Saver Starts

Q238882

The information in this article applies to:

Microsoft Windows 98
Microsoft Windows 95
Microsoft Windows NT Server version 4.0
Microsoft Windows NT Workstation version 4.0
Microsoft Windows 2000 Advanced Server
Microsoft Windows 2000 Server
Microsoft Windows 2000 Professional

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:

Install WH_GETMESSAGE Global hook.

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

Define a user-defined registered message for example, "ScreenSaverStarted".
```
   UINT WM_SCRNSVSTART = RegisterWindowMessage("ScreenSaverStarted"); 
```

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);
   }

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

Additional query words:

Keywords : kbHook kbOSWinNT400 kbOSWin2000 kbOSWin95 kbOSWin98 kbDSupport kbhowto
Issue type : kbhowto
Technology : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400xsearch kbwin2000AdvServ kbwin2000AdvServSearch kbwin2000Serv kbWinNTSsearch kbWinNTS400xsearch kbWinNTS400 kbwin2000ServSearch kbwin2000Search kbwin2000ProSearch kbwin2000Pro kbWin95search kbWin98search kbWinAdvServSearch kbZNotKeyword3 kbWin98