Q118610: Using CWnd::GetParent in a Dialog Box

Article: Q118610
Product(s): Microsoft C Compiler
Version(s): winnt:1.0,2.0,2.1,4.0
Operating System(s): 
Keyword(s): kbDlg kbMFC KbUIDesign kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbGrpDSM
Last Modified: 07-MAY-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft C/C++ for MS-DOS, version 7.0 
   - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52 
   - Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0 
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SUMMARY
=======

The window object returned by CWnd::GetParent in a modal dialog box is the
top-level window that owns the dialog box, usually the main window. It is not
necessarily the window object that has been passed to the constructor or
Create() of the CDialog object. If you need to access the parent window that was
passed in the constructor of the dialog-box object, then you need to save a copy
of this pointer in the dialog-box object.

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

When Windows creates a new popup window or a top-level window, such as a
dialog-box window, it is passed the handle of the parent window for the dialog
box. If the specified parent window is not a top-level window, then Windows
repeatedly calls GetParent until it finds the handle of a top-level window that
contains the specified parent window. Windows then sets this top-level window to
be the parent of the new popup or top-level window. So, after the new window is
created, if you call GetParent in that window, you will get the pointer to the
top-level window object that contains the original parent window that you passed
in the constructor or Create() call.

This behavior can cause problems in an MFC application if you try to create a
dialog box with a view window as the parent and then try to access the view
inside the dialog box by calling GetParent. Because the view window is not a
top-level window, Windows automatically converts the handle of the view window
to the handle of the top-level window that contains the view, which is usually
the main window of the application. Then when you call GetParent, it gets the
handle of the main window of the application and then finds the MFC object
associated with the main window. If you need to access the view window from the
dialog-box object, then you should store the pointer to the view in a member
variable of the dialog box. To do this, save a pointer to the view window in the
constructor of the dialog box or override the Create() function and have it save
the pointer.

Additional query words: 7.00 1.00 1.50 2.00 2.10 2.50 2.51 2.52 3.00 3.10 kbinf 4.00 kbNoUpdate

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Keywords          : kbDlg kbMFC KbUIDesign kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:1.0,2.0,2.1,4.0
Issue type        : kbinfo

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