Q164813: FIX: Web Browser Control Hangs in CFormView

Article: Q164813
Product(s): Microsoft C Compiler
Version(s): winnt:4.0,4.1,4.2,5.0
Operating System(s): 
Keyword(s): kbole kbInternet kbMFC kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVS97sp1fix kbGrpDS
Last Modified: 04-AUG-2001

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The information in this article applies to:

- Microsoft Visual C++, versions 4.0, 4.1 
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0 
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SYMPTOMS
========

Under certain circumstances, The Microsoft Web Browser Control may appear to
hang when used in a CFormView derived class. The control will actually be caught
in an infinitely cascading loop of focus messages.

CAUSE
=====

Microsoft Foundation Classes (MFC) has to handle focus for child items in the
modeless dialog in a CFormView.

When focus leaves the dialog, MFC remembers where the focus was. When focus
returns, MFC tries to set it back to the place where it used to be. It's
possible for a situation to exist where the window that MFC wants to set the
focus back to no longer exists.

RESOLUTION
==========

To avoid this problem, it is necessary to handle the WM_SETFOCUS message. This
handler can be added with the Class Wizard. To do this, it is necessary to
change the Class Wizard Message Filter. This can be done by choosing the Class
Info tab of the Class Wizard and selecting Window as the message filter for the
class under Advanced Options. Once this is done, you will be able to select
WM_SETFOCUS in the Message Maps tab for the CFormView derived class.

The WM_SETFOCUS message handler should look similar to the following:

     void CMyFormView::OnSetFocus(CWnd* pOldWnd)
     {
        if (!::IsWindow(m_hWndFocus) || !::IsChild(m_hWnd, m_hWndFocus))
        {
           // invalid or unknown focus window... let windows handle it
           m_hWndFocus = NULL;
           Default();
           return;
        }
        // otherwise, set focus to the last known focus window
        ::SetFocus(m_hWndFocus);
     }

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug has been corrected in Visual Studio 97
Service Pack 1.

For additional information about the Visual Studio 97 Service Pack 1, please see
the following article in the Microsoft Knowledge Base:

  Q170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION
================

The following illustrates a situation in which this problem might occur:

1. Navigate to a URL that has a child window or causes a child window to appear.

2. Put focus on the child window.

3. Navigate to a different URL.

4. Immediately set focus to a different application.

  At step 4, MFC will save the child window handle that previously had focus.
  Step 3 will eventually cause the window to be destroyed, though. So, when
  you:

5. Set focus back to the application.

MFC will try to set focus to the now-deceased child window and fail, resulting in
an infinitely cascading loop of focus messages.

Additional query words:

======================================================================
Keywords          : kbole kbInternet kbMFC kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVS97sp1fix kbGrpDSMFCATL kbNoUpdate 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbVC410 kbVC420 kbVC500 kbVC600 kbVC32bitSearch kbVC500Search
Version           : winnt:4.0,4.1,4.2,5.0
Issue type        : kbbug
Solution Type     : kbfix

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