DOCUMENT:Q113421  07-MAY-2001  [visualc]
TITLE   :PRB: Assertion Failed, WINCORE.CPP--Line 129, 133, 182, or 307
PRODUCT :Microsoft C Compiler
PROD/VER:winnt:1.0,2.0,2.1,4.0
OPER/SYS:
KEYWORDS:kbMFC KbUIDesign kbVC kbGrpDSMFCATL kbArchitecture

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

 - The Microsoft Foundation Classes (MFC), used with:
    - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, l.5, 1.51, 1.52 
    - Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

Opening a dialog box in an application that subclasses a control of the dialog
box using CWnd::SubclassDlgItem() or CWnd::SubclassWindow() causes an "Assertion
Failed!" error in WINCORE.CPP. The line number reported depends on the version
of the Microsoft Foundation Classes (MFC) being used:

    Version 2.0 for Windows    - Line 133
    Version 2.5 for Windows    - Line 182
    Version 2.0 32-bit Edition - Line 129
    Version 3.0 32-bit Edition - Line 283
    Version 3.1 32-bit Edition - Line 315
    Version 4.0 32-bit Edition - Line 307

CAUSE
=====

The second ASSERT (below) in WINCORE.CPP is the one being hit:

      BOOL CWnd::Attach(HWND hWndNew)
      {
         ASSERT(m_hWnd == NULL);   // Only attach once, detach on destroy
         ASSERT(FromHandlePermanent(hWndNew) == NULL);
            // Must not be already in permanent map
      ...

This implies that the control that we are attempting to subclass has already been
subclassed.

With MFC dialog boxes, you can specify DDX/DDV member variables to associate with
the controls of an MFC dialog class. These member variables can be real values
(for example, int, CString) or control variables (for example, CEdit, CListBox).
If the member variables are control variables, then the DDX/DDV handlers
actually do subclass the dialog box controls using the control member variables.
If you try to subclass those controls yourself, the above error can result.

RESOLUTION
==========

If you want to subclass controls yourself, then do not associate DDX/DDV
variables with those controls.

Alternatively, if you want to subclass controls but avoid the work, you can let
the DDX/DDV routines work for you. To do this, use the following steps.

1. Create a dialog box template in App Studio.

2. Use ClassWizard to associate a C++ CDialog derived class with the template.

3. In ClassWizard, with the dialog class selected, choose Edit Variables and add
   a member variable of the appropriate control type, associating it with the
   control you want to subclass. With Visual C++ 1.5, choose the Member
   Variables tab and select Add Variable to accomplish this.

4. Edit the CDialog derived class definition to change the "// Dialog Data"
   section slightly. Change the class type for the member variable from the
   default (for example CEdit), to your own class derived from that control
   class (for example, CMyEdit), as follows:

         // Dialog Data
            //{{AFX_DATA(CTestDlg)
            enum { IDD = IDD_TEST_DLG };
            CMyEdit m_EditControl;
            //}}AFX_DATA

   This will cause the control to be automatically subclassed with your own type
   of window.

Additional query words: 1.00 1.50 1.51 1.52 2.00 2.10 2.50 2.51 2.52 3.00 3.10 4.00

======================================================================
Keywords          : kbMFC KbUIDesign kbVC kbGrpDSMFCATL kbArchitecture 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:1.0,2.0,2.1,4.0
Issue type        : kbprb

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 2001.