BUG: CB_SETTOPINDEX and CB_GETTOPINDEX Always Return Zero on Macintosh

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: 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);
}