FIX: MessageBox with NULL Owner and MB_TASKMODAL (136391)
The information in this article applies to:
- The Microsoft Foundation Classes (MFC), when used with:
- Microsoft Visual C++, 32-bit Editions 2.0
- Microsoft Visual C++, 32-bit Editions 2.1
- Microsoft Visual C++, 32-bit Editions 4.0
- Microsoft Visual C++, 32-bit Editions 4.1
This article was previously published under Q136391 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.
| Modification Type: | Major | Last Reviewed: | 10/24/2003 |
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| Keywords: | kbBug kbfix kbui KB136391 |
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