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Q142274: BUG: Assertion Failure When Handling xN_SETFOCUS in CFormView

Article: Q142274
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbDocView kbMFC KbUIDesign kbVC400bug kbVC410fix kbGrpDSMFCATL kbNoUpdate
Last Modified: 06-MAY-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++ 32-bit Edition, version 4.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

Focus notifications (EN_SETFOCUS, BN_SETFOCUS, and so on) for controls in a
CFormView are usually handled in the CFormView class. Calling a function that
relies on the window handle of the control (m_hWnd) inside such a handler may
cause an assertion failure in Afxwin2.inl. This happens only if the control is
the first one in the tab order.

CAUSE
=====

The assertion failure occurs because the focus handler for the control is being
called before OnInitialUpdate() is called for the CFormView.

RESOLUTION
==========

To work around this problem, make sure that the m_hWnd member of the control is
not NULL before calling any function that relies on it.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug was corrected in Visual C++ 4.1.

Sample Code
-----------

The following illustrates calling SetSel in the for an Edit control.

      void CSettestView::OnSetFocusEdit1()
      {
          if(NULL != m_Edit.m_hWnd)
              m_Edit.SetSel( 0,1 );
      }

Additional query words: kbVC400bug 4.00 4.10

======================================================================
Keywords          : kbDocView kbMFC KbUIDesign kbVC400bug kbVC410fix kbGrpDSMFCATL kbNoUpdate 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:
Issue type        : kbbug
Solution Type     : kbfix

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