Q136391: FIX: MessageBox with NULL Owner and MB_TASKMODAL

Article: Q136391
Product(s): Microsoft C Compiler
Version(s): winnt:2.0,2.1,4.0,4.1
Operating System(s): 
Keyword(s): kbui kbnokeyword kbMFC kbVC200bug kbVC400bug kbVC410bug kbGrpDSMFCATL
Last Modified: 06-MAY-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 4.0, 4.1 
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SYMPTOMS
========

Using ::MessageBox in an application built with the Software Development Kit
(SDK) with a NULL owner window and MB_TASKMODAL disables all top-level windows
belonging to a task, as if it were a modal dialog box.

MFC, however, allows the main window to be re-enabled when clicked. For example,
if you use the following function call to bring up the message box, when you run
the application, if you click one of the application's windows, the main window
moves to the foreground and is enabled.

     ::MessageBox(NULL,
                  "Test",
                  "Test",
                  MB_OK | MB_TASKMODAL);

CAUSE
=====

The problem is due to "enable on activate" code in CFrameWnd that activates a
window when it is clicked, even if it was disabled. This works around the
Windows bug where clicking on the owner of a modal dialog box doesn't activate
the dialog box instead.

Because MFC doesn't recognize the MessageBox as a popup belonging to the
application, it will eventually call CWnd::EnableWindow(TRUE). This can be seen
in the relevant portions of the call stack below:

  ...
  CWnd::EnableWindow(TRUE)
  _AfxHandleActivate(...)
  WM_ACTIVATE message is sent.
  ...
  CWnd::SetForegroundWindow()
  _AfxHandleSetCursor(...)           //popups checked here.
  WM_SETCURSOR message is sent.
  ...

The most recently called function is at the top of the list.

RESOLUTION
==========

To work around this problem, use CWnd::MessageBox or AfxMessageBox instead of
::MessageBox. If you must use ::MessageBox, specify a window as the owner rather
than using NULL as the first parameter. For example, to specify the
application's main window as the owner, use this code:

  ::MessageBox(AfxGetMainWnd()->m_hWnd,
               "Test",
               "Test",
               MB_OK | MB_TASKMODAL);

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug was fixed in Visual C++ versions 4.2 and
later.

Additional query words: 2.00 2.10 3.00 3.10 4.00 4.10 MessageBox Modeless

======================================================================
Keywords          : kbui kbnokeyword kbMFC kbVC200bug kbVC400bug kbVC410bug kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:2.0,2.1,4.0,4.1
Issue type        : kbbug
Solution Type     : kbfix

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