WinHelp is called two times when you press F1 in an AppWizard-generated MFC application

View products that this article applies to.

This article was previously published under Q139696

Expand all | Collapse all

SYMPTOMS

In an AppWizard-generated MFC application with context-sensitive help support, pressing F1 causes WinHelp to be called twice. In most cases, the application displays the correct help topic. In some cases, however, the application displays the wrong help topic. This can happen when the user clicks a toolbar button and presses F1 before releasing the mouse button.

This occurs only under the operating systems that support the WM_HELP message, such as Windows 95 or Windows NT 4.0.

Back to the top

CAUSE

CWnd in MFC 4.0 has a handler for WM_HELP that sends a WM_COMMAND with an id of ID_HELP. The AppWizard-generated application also has an accelerator for the F1 key. Both result in WinHelp being called.

Back to the top

RESOLUTION

There are two possible resolutions:

Remove the accelerator table entry for F1. The problem with this is that F1 help will no longer work in Windows NT 3.5 or Win32s because these operating systems do not support the WM_HELP message. -or-

Override CWinApp::PreTranslateMessage and cancel routing of the F1 key down message as follows:

      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 CHelpStuffApp::PreTranslateMessage(MSG* pMsg)
      {
         // If on a system that supports WM_HELP, cancel
         // routing of F1 key.
         DWORD dwVersion = ::GetVersion();
         UINT nWinVer = (LOBYTE(dwVersion) << 8) + HIBYTE(dwVersion);
         if (nWinVer >= 0x333 && IsHelpKey(pMsg))
             return TRUE;

         return CWinApp::PreTranslateMessage(pMsg);
      }

Back to the top