Q125728: FIX: Problems Occur After Destroying Dockable CControlBar

Article: Q125728
Product(s): Microsoft C Compiler
Version(s): 2.0
Operating System(s): 
Keyword(s): kbProgramming kbMFC KbUIDesign kbVC200bug kbVC210fix kbGrpDSMFCATL kbMFCCtrlBarkbbuglis
Last Modified: 11-FEB-2002

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Editions, version 2.0 
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SYMPTOMS
========

Destroying a dockable CControlBar object may cause unexpected behavior. For
example, an exception may be thrown that if not caught will generate a message
box containing something similar to this:

  

 Unhandled Exception in myapp.exe (MFC30D.DLL):
 0xC0000005: Access Violation.

By using the debugger, you will likely see that this Access Violation has
occurred in the function CObject::IsKindOf.

CAUSE
=====

This problem occurs because of the way toolbars are handled by the framework.
MFC implements a CDockBar object for use as the parent of dockable control bars.
To arrange the control bars docked at the location it manages, this CDockBar
object maintains a list of the CControlBar objects that it has as children.

The CControlBar destructor does not remove the control bar from the CDockBar's
list of control bars. Subsequent attempts by the CDockBar object to manipulate
the pointer maintained in its list will cause unpredictable behavior such as an
Access Violation.

RESOLUTION
==========

To work around the problem, make sure that dockable toolbars are removed from
their parent CDockBar objects before destroying them.

To do this, call CDockBar::RemoveControlBar before destroying the ControlBar
object. You will need to include the header file <afxpriv.h> to be able to
call this function. For example:

Change this:

     #include "stdafx.h"
     ...
     ...
     void SomeFunction()
     {
       delete pToolBar;
     }

To this:

     #include "stdafx.h"
     #include <afxpriv.h>
     ...
     ...
     void SomeFunction()
     {
       if(pToolBar->m_pBar!=NULL)
         pToolBar->m_pBar->RemoveControlBar(pToolBar);
       delete pToolBar;
     }

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++ version 2.1 (MFC
3.1).

Additional query words: 3.00 toolbar CToolBar

======================================================================
Keywords          : kbProgramming kbMFC KbUIDesign kbVC200bug kbVC210fix kbGrpDSMFCATL kbMFCCtrlBar kbbuglist kbfixlist
Technology        : kbAudDeveloper kbMFC
Version           : :2.0
Issue type        : kbbug
Solution Type     : kbfix

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

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