PRB: MFC ActiveX Control in IE Doesn't Detect Keystrokes

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This article was previously published under Q168777

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SYMPTOMS

Accelerator keys, such as ARROW keys, are first received by the message pump of the ActiveX control's container. Even if the control has the focus, it does not receive messages for keystrokes that have special meaning to control containers, such as ARROW and TAB keys. MFC ActiveX controls have a chance to intercept these messages by overriding their PreTranslateMessage function.

However, PreTranslateMessage is not always called for an MFC ActiveX control.

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CAUSE

PreTranslateMessage in an MFC ActiveX control is called by the TranslateAccelerator method of the IOleInPlaceActiveObject interface of the control. Internet Explorer only calls this method for the control that is currently UI-Active. Only one control can be UI-Active at a time.

Internet Explorer does not automatically UI-Activate any controls when a page is first loaded. Internet Explorer waits until the user tabs to an ActiveX control on the page to UI-Activate it. Also, MFC ActiveX controls UI-Activate themselves when they are clicked with the mouse. In an MFC ActiveX control, this is done in COleControl::OnLButtonUp.

If you have a child control inside your COleControl, mouse-click messages on the child control are not sent to the COleControl and MFC does not UI- Activate the ActiveX control, even though the child control has just been given the keyboard focus. Internet Explorer intercepts the keystrokes and does not give the control a chance to filter them in PreTranslateMessage.

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RESOLUTION

Here is a typical PreTranslateMessage. This code forwards ARROW, HOME, and END keys back to the control so that they can be received using a MESSAGE_MAP entry:

   // trap keys and forward on to the control
   BOOL CMyActiveXCtrl::PreTranslateMessage(MSG* pMsg)
   {
      switch (pMsg->message)
      {
         case WM_KEYDOWN:
         case WM_KEYUP:
            switch (pMsg->wParam)
            {
               case VK_UP:
               case VK_DOWN:
               case VK_LEFT:
               case VK_RIGHT:
               case VK_HOME:
               case VK_END:
                  SendMessage (pMsg->message, pMsg->wParam, pMsg->lParam);
                  // Windowless controls won't be able to call SendMessage.
                  // Instead, just respond to the message here.
                  return TRUE;
            }
            break;
      }
      return COleControl::PreTranslateMessage(pMsg);
   }

If you have a child control within your ActiveX control, you need to UI-Activate the whole control whenever that child control is activated. For example, if you have an edit control inside your ActiveX control, add a handler as follows to your ActiveX control class:

   int CMyActiveXCtrl::OnMouseActivate(CWnd* pDesktopWnd, UINT nHitTest, UINT
   message)
   {
      if (!m_bUIActive)
          OnActivateInPlace (TRUE, NULL); // == UI-Activate the control
      return COleControl::OnMouseActivate(pDesktopWnd, nHitTest, message);
   }

Because Internet Explorer may not immediately UI-Activate a control, even if that is the only control on the page, it may be desirable to automatically request a UI-Activation when the control is created. This can be done during the COleControl::OnCreate (WM_CREATE) handler. Windowless controls do not get WM_CREATE or any windows messages; therefore, this code won't work in a windowless control. Also note that this does not guarantee that a control will remain UI-Activated. If there are other controls on a page that request UI-Activation in a similar manner, only one will eventually be UI-Activated and receive keystroke messages as described. And if the user TABs away from an ActiveX Control, Internet Explorer will automatically UI-deactivate the control.

   int CMyActiveXCtrl::OnCreate(LPCREATESTRUCT lpCreateStruct)
   {
      if (COleControl::OnCreate(lpCreateStruct) == -1)
         return -1;
      OnActivateInPlace (TRUE, NULL); // == UI-Activate the control
      return 0;
   }

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