Q143209: PRB: MeasureItem Not Called for Popup Item on Owner-Draw Menu

Article: Q143209
Product(s): Microsoft C Compiler
Version(s): winnt:1.0,2.0,2.1,2.2,4.0
Operating System(s): 
Keyword(s): kbcode kbMenu kbMFC KbUIDesign kbVC100 kbVC150 kbVC200 kbVC400 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 1.0, 2.0, 2.1, 2.2, 4.0 
   - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52 
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SYMPTOMS
========

The CMenu::MeasureItem() function for an owner-draw menu isn't called for those
menu items that bring up submenus.

CAUSE
=====

This is a limitation of the self-drawing capability of MFC owner-draw menus.

RESOLUTION
==========

For owner-draw menus that contain sub-popup menus, handle the WM_MEASUREITEM in
the owning window. See the "Sample Code" section in this article for an example.

STATUS
======

This behavior is by design.

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

A menu item that brings up a submenu has no real ID associated with it. Instead
the ID for this popup placeholder is actually the HMENU for the submenu
associated with that item. As for all owner-draw menu items, Windows will send a
WM_MEASUREITEM message to the application, specifying the address of a
MEASUREITEMSTRUCT structure in lParam. The application should fill in this
structure with the dimensions of the menu item. Now because the submenu item has
an HMENU instead of an ID, this is the value that is passed in the idFrom
variable of this structure. Essentially, an application that handles this
message must recognize when this is an HWND for a valid submenu item. As of MFC
4.0, MFC's implementation of CWnd::OnMeasureItem() does not make this
determination correctly.

An examination of the MFC source will reveal the problem. When
CWnd::OnMeasureItem() is called by the receipt of this message, it uses
FindPopupMenuFromID() to find the menu associated with a particular ID, so that
the call pMenu->MeasureItem(...) can be made. Unfortunately
FindPopupMenuFromID() does not check the case where the ID might be an HMENU. It
will always return NULL in this case; therefore, the call to MeasureItem() will
never be made.

Sample Code
-----------

The following sample code demonstrates how to implement OnMeasureItem when the
menu item in question is a submenu. m_hMenuSub is a member variable that was
initialized when the menu was created. If the item is not a submenu, the MFC
self-drawing menu code can still be used.

  /* Compile options needed:  Default
  */ 
  void COwnerWindow::OnMeasureItem(int nIDCtl, LPMEASUREITEMSTRUCT
                                                    lpMeasureItemStruct)
  {
      if ( lpMeasureItemStruct->CtlType == ODT_MENU &&
           IsMenu((HMENU)lpMeasureItemStruct->itemID) &&
           lpMeasureItemStruct->itemID == (UINT)m_hMenuSub )
      {
          // MFC's self-drawing won't work in this case
          // go ahead and handle it here
          lpMeasureItemStruct->itemWidth = 100;
          lpMeasureItemStruct->itemHeight = 20;
      }
      else
          // let MFC's self-drawing handle it
          CFrameWnd::OnMeasureItem(nIDCtl, lpMeasureItemStruct);
  }

(c) Microsoft Corporation 1999, All Rights Reserved.
Contributions by Jason Strayer, Microsoft Corporation


Additional query words: 1.00 1.50 2.50 2.51 2.52 2.00 2.10 2.20 3.00 3.10 3.20 4.00

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Keywords          : kbcode kbMenu kbMFC KbUIDesign kbVC100 kbVC150 kbVC200 kbVC400 kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:1.0,2.0,2.1,2.2,4.0
Issue type        : kbprb

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