Q201116: BUG: CB_SETTOPINDEX and CB_GETTOPINDEX Always Return 0 on Mac

Article: Q201116
Product(s): Microsoft C Compiler
Version(s): MACINTOSH:4.0,4.0b
Operating System(s): 
Keyword(s): kbHWMAC kbMFC kbVC kbVC400bug kbDSupport kbGrpDSMFCATLkbbuglist
Last Modified: 11-MAR-2000

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Visual C++, Macintosh Cross-Development Addon, versions 4.0, 4.0b 
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SYMPTOMS
========

On the Macintosh, the combo box messages CB_GETTOPINDEX and CB_SETTOPINDEX fail
and always return zero (0).

CAUSE
=====

There are no message handlers for these messages in the combo-box window
procedure in the Windows Portability Library.

RESOLUTION
==========

Obtain a pointer to the list box portion of the combo box, and use
LB_GETTOPINDEX and LB_SETTOPINDEX instead.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.

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

The combo-box control is composed of an edit control and a list-box control. For
additional information about combo boxes, please see the following article in
the Microsoft Knowledge Base:

  Q65881 INFO: The Parts of a Windows Combo Box and How They Relate

On the Intel side, the edit control is the first child of the combo box. For a
simple combo box, the Macintosh has the list-box control as the first control.

The window handle to the list box can be obtained using GetWindow. Once a valid
handle is obtained, using the LB_GETTOPINDEX and LB_SETTOPINDEX messages
provides the same functionality as CB_GETTOPINDEX and CB_SETTOPINDEX.

The sample code below shows the MFC implementation:

Sample Code:

  class CCtrlsView : public CFormView
  {
  public:
     CComboBox   m_comboindex;
     int      m_currentIndex;
  #ifdef _MAC
     CListBox m_comboList;
  #endif
  ...
  };

  void CCtrlsView::OnInitialUpdate()
  {
     CFormView::OnInitialUpdate();

  #ifdef _MAC
     // Obtain pointer to combo's list box.
     HWND hComboList = m_comboindex.GetWindow(GW_CHILD)->m_hWnd;
     ASSERT(hComboList);

     // Verify class name.
     char className[50];
     GetClassName(hComboList, className, 50);
     ASSERT(lstrcmp(className, "ComboLBox") == 0);

     // Subclass to use CListBox.
     m_comboList.SubclassWindow(hComboList);
  #endif
  ...
  }

  // A simple combo box with "set" and "get" buttons using
  // the values from an edit control.
  void CCtrlsView::OnSetindex()
  {
     UpdateData(TRUE);
  #ifndef _MAC
     m_comboindex.SetTopIndex(m_currentIndex);
  #else
     m_comboList.SetTopIndex(m_currentIndex);
  #endif
  }

  void CCtrlsView::OnGetindex()
  {
  #ifndef _MAC
     m_currentIndex = m_comboindex.GetTopIndex();
  #else
     m_currentIndex = m_comboList.GetTopIndex();
  #endif
     UpdateData(FALSE);
  }

REFERENCES
==========

(c) Microsoft Corporation 1999, All Rights Reserved. Contributions by Adam Kim,
Microsoft Corporation.


Additional query words: Macintosh CB_GETTOPINDEX CB_SETTOPINDEX combobox listbox

======================================================================
Keywords          : kbHWMAC kbMFC kbVC kbVC400bug kbDSupport kbGrpDSMFCATL kbbuglist
Technology        : kbVCsearch kbHWMAC kbOSMAC kbAudDeveloper kbVCXDev400Mac kbVCXDev400bMac
Version           : MACINTOSH:4.0,4.0b
Issue type        : kbbug

=============================================================================

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