FIX: Assertion Failure When Handling xN_SETFOCUS in CFormView

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included 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 );
    }