PRB: WM_HELP Message Not Received When F1 Pressed on Menu

• The Microsoft Foundation Classes (MFC), included with:
  • Microsoft Visual C++ 32-bit Edition, versions 2.1, 2.2

SYMPTOMS

Windows 95 and Windows NT version 3.51 support a new Windows message, WM_HELP. If a menu is active when F1 is pressed, WM_HELP should be sent to the window associated with the menu by Windows. However, with an MFC application, the WM_HELP message never gets sent.

This problem does not occur in Visual C++ 4.0 or later

CAUSE

MFC defines default handling of the F1 key to bring up help for menu items. For more information about F1 help within an MFC application, please see MFC Technote #28 and the Scribble Tutorial.

The F1 key is handled by the CWinThread::ProcessMessageFilter() function. It causes the MFC function OnCommandHelp() to be called, which brings up help for the currently selected menu item.

RESOLUTION

To work around this behavior, either use the help system provided by MFC, or override ProcessMessageFilter() for your CWinApp-derived class to by-pass the MFC processing of the F1 key. For example, the code might look like this:

static BOOL AFXAPI IsHelpKey(LPMSG lpMsg)
   // return TRUE only for non-repeat F1 keydowns.
{
   return lpMsg->message == WM_KEYDOWN &&
#ifndef _MAC
         lpMsg->wParam == VK_F1 &&
#else
         lpMsg->wParam == VK_HELP &&
#endif
         !(HIWORD(lpMsg->lParam) & KF_REPEAT) &&
         GetKeyState(VK_SHIFT) >= 0 &&
         GetKeyState(VK_CONTROL) >= 0 &&
         GetKeyState(VK_MENU) >= 0;
}

BOOL CYourApp::ProcessMessageFilter(int code, LPMSG lpMsg)
{
   if (IsHelpKey(lpMsg))
      return FALSE;  // pass on to Windows to do WM_HELP
                           // processing - don't use default MFC
                           // help processing

   return CWinApp::ProcessMessageFilter(code, lpMsg);
} 

REFERENCES

For more information about adding F1 help to your application, please see the following article in the Microsoft Knowledge Base:

Q110506 SAMPLE: Context Sensitive Help in a CDialog

• MFC Technote#28 in the online documentation



• Scribble tutorial in the online documentation



• The MFC Encyclopedia under the "Help" topic

Additional query words: 2.10 2.20 3.1 3.10 3.2 3.20 4.00 Win95

Keywords : kbcode kbnokeyword kbMFC kbVC
Version : winnt:
Platform : winnt
Issue type :