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Q155436: DOC: CImageList Returned from CreateDragImage Needs Delete

Article: Q155436
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbdocfix kbdocerr kbMFC KbUIDesign kbVC kbVC420bug kbVC500fix 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 Edition, version 4.2 
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SUMMARY
=======

The CTreeCtrl::CreateDragImage and CListCtrl::CreateDragImage functions in
versions of MFC earlier than 4.2 return a pointer to a temporary CImageList
object. In MFC version 4.2, CreateDragImage returns a permanent object that must
be explicitly deleted.

The documentation for CreateDragImage does not state this.

This documentation error was fixed in Visual C++ version 5.0.

MORE INFORMATION
================

In versions of MFC earlier than 4.2, MFC implements CreateDragImage as
CImageList::FromHandle. An object returned from FromHandle is temporary and does
not need to be explicitly deleted. A limitation of this implementation is that
the CImageList pointer can be safely used only in the current message being
processed.

CreateDragImage function was changed in Visual C++ version 4.2 to allocate a
permanent CImageList object, and can now be used when handling multiple
messages. When finished using the pointer returned by CreateDragImage, however,
it is now necessary to explicitly delete the object:

     CImageList* pImageList = CreateDragImage( ...
     delete pImageList;

For more information on temporary handles returned from FromHandle, see MFC
TechNote "TN003: Mapping of Windows Handles to Objects" in the Visual C++ Books
Online.

Additional query words: kbVC420bug leak kbImgLst

======================================================================
Keywords          : kbdocfix kbdocerr kbMFC KbUIDesign kbVC kbVC420bug kbVC500fix kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:
Solution Type     : kbfix

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