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Posted on 2004-03-24
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Last Modified: 2010-04-01
I made a simple program with a systemwide keyboardhook using SetWindowsHookEx with LowLevelKeyboardProc.
here's the code:
****************
LRESULT CALLBACK LowLevelKeyboardProc(int nCode, WPARAM wParam, LPARAM lParam)

{

  BOOL fHandled = FALSE;
  if (nCode == HC_ACTION)
  {
      KBDLLHOOKSTRUCT *pkbdllhook = (KBDLLHOOKSTRUCT *)lParam;
          switch (pkbdllhook->vkCode)
      {
          case VK_F12:

                      CTraa_004Dlg* maind = (CTraa_004Dlg*)theApp.GetMainWnd();
                      MessageBox(0,"ef","12",0);        
                      fHandled = TRUE;
                            break;
          }
  }

  return (fHandled ? TRUE : CallNextHookEx(ghhookKB, nCode, wParam, lParam));
}
*******************
now, my questions are:
1/I was told that something which is systemwide has to be in a dll, but it works, and it is an exe.
2/It works, but the MessageBox gets called twice  (when I press F12) I don't understand why...

thanks
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Question by:lapijn
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6 Comments
 
LVL 48

Expert Comment

by:AlexFM
ID: 10666959
1) Global keyboard hook with WH_KEYBOARD parameter must use Dll. WH_KEYBOARD_LL hook which can be used in WinNT or later works without Dll.
2) It is called twice - first time for WM_KEYDOWN message, second time for WM_KEYUP message. Test wParam for this.
0
 

Author Comment

by:lapijn
ID: 10672596
thanks.
But how should I set WM_KEYDOWN ?? I tried to set it as a default parameter, but apparently this doesn't does the job...
0
 
LVL 48

Accepted Solution

by:
AlexFM earned 600 total points
ID: 10674896
LRESULT CALLBACK LowLevelKeyboardProc(int nCode, WPARAM wParam, LPARAM lParam)

{

  BOOL fHandled = FALSE;
  if (nCode == HC_ACTION)
  {
      if ( wParam == WM_KEYDOWN )
      {
       KBDLLHOOKSTRUCT *pkbdllhook = (KBDLLHOOKSTRUCT *)lParam;
           switch (pkbdllhook->vkCode)
       {
           case VK_F12:

                       CTraa_004Dlg* maind = (CTraa_004Dlg*)theApp.GetMainWnd();
                       MessageBox(0,"ef","12",0);        
                       fHandled = TRUE;
                             break;
       }
   }
  }

  return (fHandled ? TRUE : CallNextHookEx(ghhookKB, nCode, wParam, lParam));
}

Now MessageBox is shown once.
0
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Author Comment

by:lapijn
ID: 10676233
thanks. It works.
(However, I can only press the OK button after 5 seconds).
0
 
LVL 48

Expert Comment

by:AlexFM
ID: 10676310
Never use MessageBox and any other interaction functions inside of hook function. For testing purposes use TRACE.
0
 

Author Comment

by:lapijn
ID: 10676930
ok.thanks.
0

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