BETA-PRB: ActiveX Control Is the Parent Window of Modeless Dialog

• The Microsoft Foundation Classes (MFC), used with:
  • Microsoft Visual C++, 32-bit Editions, versions 4.2, 4.2b, 5.0

SYMPTOMS

When an ActiveX control is the parent window of a modeless dialog box or propertysheet window, the TAB key, arrow keys, and accelerator keys don't work as expected. The TAB key doesn't move input focus from one control to another. Pressing the arrow keys or accelerator keys in the modeless dialog box or propertysheet window has no effect.

CAUSE

The problem is the ActiveX control doesn't own the message pump. The message pump is owned by the container application. Therefore, all the keystroke messages are taken by the container application and not dispatched to the modeless dialog box or propertysheet window.

The problem does not occur with a modal dialog box/propertysheet window because the message pump is owned by the dialog box manager, and it takes care of handling all keystroke messages.

RESOLUTION

Install a Windows WH_GETMESSAGE hook for the modeless dialog box/propertysheet derived class to allow it to intercept keystrokes and handle accelerators.

STATUS

This behavior is by design.

MORE INFORMATION

The following sample shows a way to install the Windows message hook to a modeless CPropertySheet-derived class:

Sample Code

   // Handle to the Windows Message hook. It can be a global variable or a
   // member variable in your CPropertySheet-derived class.
   HHOOK hHook = NULL;



   // Hook procedure for WH_GETMESSAGE hook type.
   LRESULT CALLBACK GetMessageProc(int nCode, WPARAM wParam, LPARAM lParam)
   {
      // Switch the module state for the correct handle to be used.
      AFX_MANAGE_STATE(AfxGetStaticModuleState( ));



      // If this is a keystrokes message, translate it in controls'
      // PreTranslateMessage().
      LPMSG lpMsg = (LPMSG) lParam;
      if( (nCode >= 0) &&
         PM_REMOVE == wParam &&
         (lpMsg->message >= WM_KEYFIRST && lpMsg->message <= WM_KEYLAST) &&
         AfxGetApp()->PreTranslateMessage((LPMSG)lParam) )
         {
         // The value returned from this hookproc is ignored, and it cannot
         // be used to tell Windows the message has been handled. To avoid
         // further processing, convert the message to WM_NULL before
         // returning.
         lpMsg->message = WM_NULL;
         lpMsg->lParam = 0L;
         lpMsg->wParam = 0;
         }



      // Passes the hook information to the next hook procedure in
      // the current hook chain.
      return ::CallNextHookEx(hHook, nCode, wParam, lParam);
   }



   // Declare and define the following two functions:
   BOOL CModelessPropertySheet::OnInitDialog()
   {
      CPropertySheet::OnInitDialog();

      // Install the WH_GETMESSAGE hook function.
      hHook = ::SetWindowsHookEx(
         WH_GETMESSAGE,
         GetMessageProc,
         AfxGetInstanceHandle(),
         GetCurrentThreadId());
      ASSERT (hHook);



      return TRUE;   // Return TRUE unless you set the focus to a control.
                     // EXCEPTION: OCX Property Pages should return FALSE.


   }



   void CModelessPropertySheet::OnClose()
   {
      // Uninstall the WH_GETMESSAGE hook function.
      VERIFY (::UnhookWindowsHookEx (hHook));



      CPropertySheet::OnClose();


   }
 

Steps to Reproduce the Problem

1. Select the MFC ActiveX ControlWizard to create an ActiveX control. Accept all the default settings.



2. Display a modeless dialog box or propertysheet window when double-clicking inside the control.

REFERENCES

(c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Yeong- Kah Tam, Microsoft Corporation.

Additional query words: ocx kbcodesam tabs hooks dll mfcdll

Keywords : kbcode kbActiveX kbVC420 kbVC500 kbMFC500 kbMFC420
Version : winnt:4.2,4.2b,5.0
Platform : winnt
Issue type : kbprb