PRB: Activation of VB MDI Child Window and ActiveX Control

• The Microsoft Foundation Classes (MFC), included with:
  • Microsoft Visual C++, 32-bit Editions, versions 5.0, 6.0

SYMPTOMS

The following two problems occur when embedding an ActiveX control in an MDI application written in Visual Basic:

• Clicking the ActiveX control that is embedded in the MDI child form does not activate the MDI child window; however, clicking other areas works correctly.



• In Visual Basic 5.0, when focus is in the ActiveX control, pressing CTRL+TAB doesn't activate the next MDI child window in the MDI application.
  
  NOTE: This problem has been corrected in Visual Basic 6.0.

CAUSE

These problems are caused by the controls having the WS_EX_NOPARENTNOTIFY style. Windows's MDI child activation is based on the MDI client window getting the WM_PARENTNOTIFY message. However, this message is suppressed when the WS_EX_NOPARENTNOTIFY style is specified. Visual Basic does not address this scenario, which causes the problems to occur.

RESOLUTION

Correcting these problems from the control site can be done in the following ways:

• Remove the WS_EX_NOPARENTNOTIFY extended style from the ActiveX control's window. This can be done by overriding PreCreateWindow() and unsetting the style bit.



• For Visual Basic 5.0 clients, send a WM_MDINEXT message to the parent window of the MDI child window (for example, the MDI client window) so the next MDI child window can be activated.

STATUS

Microsoft is researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

PreCreateWindow() is a CWnd virtual function that accesses the CREATESTRUCT structure for the window just prior to its creation. The WS_EX_NOPARENTNOTIFY window style is an extended style, and can be unset in the following manner:

   BOOL CFocusCtrl::PreCreateWindow(CREATESTRUCT& cs)
   {
      cs.dwExStyle &= ~WS_EX_NOPARENTNOTIFY;
      return COleControl::PreCreateWindow(cs);
   } 

   HWND CFocusCtrl::GetMDIChildHwnd()
   {
      // Get the window associated with the in-place site object,
      // which is connected to this ActiveX control.
      HWND hparent;
      if (m_pInPlaceSite != NULL)
         m_pInPlaceSite->GetWindow(&hparent);

      // Loop until either an MDI child window or no parent window is
      // found. MDI child window will have a WS_EX_MDICHILD window
      // style.
      CWnd* parent = FromHandle(hparent);
      do
      {
         if (parent == NULL)
            break;

         // Check to see whether or not it is an MDI child window.
         // Returns the HWND of the MDI child window to the caller.
         DWORD style = parent->GetExStyle();
         if (style & WS_EX_MDICHILD)
            return parent->GetSafeHwnd();

         parent = parent->GetParent();
      }
      while (1);

      return NULL;
   }

   void CFocusCtrl::OnKeyDown(UINT nChar, UINT nRepCnt, UINT nFlags)
   {
      if ((GetKeyState(VK_CONTROL) < 0) && nChar == VK_TAB)
         {
            // Activate next MDI child window in the MDI application by
            // sending a message to the client window (the parent
            // of the MDI child window).
            CWnd* mdichild = CWnd::FromHandle(GetMDIChildHwnd());
            if (mdichild)
               (mdichild->GetParent())->SendMessage(WM_MDINEXT);
         }

      COleControl::OnKeyDown(nChar, nRepCnt, nFlags);
   } 

Steps to Reproduce Behavior

1. Create an MDI application in Visual Basic.



2. Add an ActiveX control and a textbox control to the MDI child form in design mode.



3. Run the MDI application. The MDI application will show an MDI child window during startup.



4. On the File menu, click New to create another MDI child window. Tile both MDI child windows. You will notice that one MDI child window is active and the other is inactive.



5. Click the ActiveX control of the inactive MDI child window; the MDI child window is not activated. Click another area other than the ActiveX control in the inactive MDI child window; the MDI child window changes from an inactive to an active state.

REFERENCES

For information about creating an MDI application in Visual Basic, please refer to Visual Basic's books online.

For additional information about getting the actual parent of an ActiveX control, please see the following article in the Microsoft Knowledge Base:

Q150204 HOWTO: Retrieve the Actual Parent Window of an ActiveX Control

Additional query words:

Keywords : kbole kbActiveX kbMFC kbVC kbVC500 kbVC600
Version : WINNT:5.0,6.0
Platform : winnt
Issue type : kbprb