Q148498: DOC: CListBox::ItemFromPoint() Works Only in Windows 95

Article: Q148498
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbcode kbdocfix kbdocerr kbMFC KbUIDesign kbVC210bug kbVC220bug kbVC400bug kbVC410bug k
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, versions 2.1, 2.2, 4.0, 4.1 
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SUMMARY
=======

The CListBox member function ItemFromPoint() is not implemented in Win32s or
Windows NT, but the documentation for the member function does not state this
fact.

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

The ItemFromPoint() member function relies on the LB_ITEMFROMPOINT message which
the documentation correctly states is supported only in Windows 95.

The Win32 SDK function LBItemFromPt() could be used as an alternative to
CListBox::ItemFromPoint(). The drawback is LBItemFromPt() does not have exactly
the same functionality. However, the workaround demonstrated in the folloiwng
sample code does provide the same functionality.

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

The following code shows how ItemFromPoint() can be implemented to behave the
same way on Windows 95, Win32s, and Windows NT. In this sample code, CMyListBox
is derived from CListBox:

  UINT CMyListBox::ItemFromPoint(CPoint pt,BOOL &bOutside)
  {
    // If we are on Win95, just call the base class
    if((BYTE)::GetVersion() >= 4)
      return CListBox::ItemFromPoint(pt,bOutside);

    if(GetCount()<1)
    {
      bOutside=TRUE;
      return 0;
    }

    CRect rectClient;
    GetClientRect(&rectClient);

    bOutside=!rectClient.PtInRect(pt);

    if (pt.y < rectClient.top)
      pt.y = rectClient.top;
    if (pt.x < rectClient.left)
      pt.x = rectClient.left;

    CRect rectCheck;
    int lastY = -1;

    for ( int nIndex = GetTopIndex(); nIndex < GetCount(); nIndex++)
    {
      GetItemRect(nIndex , &rectCheck);
      rectCheck.right+=1;
      if(!rectClient.PtInRect(rectCheck.TopLeft()))
        break;

      if (rectCheck.PtInRect(pt))
        return nIndex;

      // check for case where mouse is below the last item in a column of
      // an LBS_MULTICOLUMN list box
      if ( GetStyle() & LBS_MULTICOLUMN &&
           nIndex < GetCount()-1 &&
           pt.x>=rectCheck.left &&
           pt.x<rectCheck.right)
      {
          CRect rectNext;
          GetItemRect(nIndex+1, &rectNext);
          if (rectNext.left > rectCheck.left)
              return nIndex;
      }

      if (pt.y>=rectCheck.top)
          lastY = nIndex;
    }

    return lastY;
  }

This documentation error was corrected in Visual C++ 32-bit Edition version 4.2.

Additional query words: kbVC400bug 2.10 2.20 4.00 4.10 4.20 3.10 3.20 vcfixlist420

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Keywords          : kbcode kbdocfix kbdocerr kbMFC KbUIDesign kbVC210bug kbVC220bug kbVC400bug kbVC410bug kbVC420fix kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:
Solution Type     : kbfix

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