INFO: CFrameWnd Objects Can Destroy Themselves (88557)
The information in this article applies to:
- The Microsoft Foundation Classes (MFC), when used with:
- Microsoft Visual C++, 32-bit Professional Edition
- Microsoft Visual C++, 32-bit Enterprise Edition
- Microsoft Visual C++, 32-bit Learning Edition
This article was previously published under Q88557
7.00 | 1.00 1.50 1.51 1.52 | 1.00 2.00 2.10 4.00
MS-DOS | WINDOWS | WINDOWS NT
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SUMMARY
Objects derived from the CFrameWnd class destroy themselves automatically
when the Window that is associated with the object processes the
WM_NCDESTROY message. Because objects derived from CFrameWnd classes
destroy themselves, it is recommended that applications use the "new"
operator to create new instances of this class on the heap.
MORE INFORMATION
Objects derived from CFrameWnd are designed to "clean up" after themselves.
The CFrameWnd class overloads the OnNcDestroy() member function that makes
a call to the PostNcDestroy() member function, which in turn does a "delete
this."
CMDIFrameWnd and CMDIChildWnd, which are derived from CFrameWnd, exhibit
identical behavior.
The OnNcDestroy() function is called when the window receives the
WM_NCDESTROY message. This is the last message a window receives. As a
result, CFrameWnd objects should be created on the heap using the "new"
operator, and should never be explicitly deleted by the application. If the
application needs to destroy the object, it should use the DestroyWindow()
member function, which destroys both the window and its CFrameWnd object.
In general, CFrameWnd objects should not be used as local variables in
functions or as embedded objects in other classes. Doing so may cause the
object's destructor to be called twice: once when the user closes the
window, and once when the function containing the local variable goes out
of scope or when the object containing the embedded CFrameWnd object is
deleted. Attempting to delete the object more than once may cause an
unrecoverable application error (UAE).
You can create a CFrameWnd-derived object on the stack or as a static
object if the application overrides the PostNcDestroy() function for the
derived class. PostNcDestroy() is a virtual member function of the CWnd
class that is called by the OnNcDestroy() function. The overridden
PostNcDestroy() function for the derived class should do nothing, rather
than "delete this." This prevents the object from being destroyed twice.
| Modification Type: | Major | Last Reviewed: | 12/12/2003 |
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| Keywords: | kbArchitecture kbDocView kbinfo KbUIDesign KB88557 |
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