DOCUMENT:Q200099  06-FEB-2000  [visualc]
TITLE   :PRB: Owner-Drawn List Control in 68K App Crashes Macintosh
PRODUCT :Microsoft C Compiler
PROD/VER:MACINTOSH:4.0b
OPER/SYS:
KEYWORDS:kbHWMAC kbVC kbDSupportkbbuglist

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

 - Microsoft Visual C++, Macintosh Cross-Development Addon, version 4.0b 
-------------------------------------------------------------------------------

SYMPTOMS
========

When displaying an owner-drawn ListView control in report view on a 68K
Macintosh, the Macintosh system crashes displaying the following message:

   Sorry, a system error occurred.
   "application name"
   divide by zero

If the program is executed under the debugger, Developer Studio displays the
following message:

   Exception in xxx.exe: 0x00000004: Divide by Zero

CAUSE
=====

A bug with the height initialization of the ListView item for the control causes
the internal call to ShowWindow to perform a divide-by-zero operation.

RESOLUTION
==========

Set the height of the ListView control item to an appropriate value in the
parent window's WM_MEASUREITEM handler for the ListView control. This can be
done through the itemHeight field of the LPMEASUREITEMSTRUCT structure pointer
provided.

STATUS
======

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

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

The workaround involves setting the itemHeight data member of the
LPMEASUREITEMSTRUCT structure pointer before the control is displayed. This can
be done only in the parent window's WM_MEASUREITEM handler. It is not necessary
to initially create the control without the WS_VISIBLE flag.

The code below shows an example for an owner-drawn ListView control in a form
view. The default height of a ListView control item on the Macintosh is 14
pixels.

   BEGIN_MESSAGE_MAP(CMyView, CFormView)
       ON_WM_MEASUREITEM()
       ...
   END_MESSAGE_MAP()

   // WM_MEASUREITEM is sent to parent of list control
   void CMyView::OnMeasureItem(int nIDCtl,
       LPMEASUREITEMSTRUCT lpMeasureItemStruct)
   {
       if (nIDCtl == IDC_LIST1) {

           // Calculate appropriate font height.
           int newHeight = 0;
           CFont* pFont = (CFont*)GetFont();
           if (pFont) {
               LOGFONT lf;
               pFont->GetLogFont(&lf);
               newHeight = (lf.lfHeight > 0) ? lf.lfHeight : -lf.lfHeight;
           }

           // Set new itemHeight, use 14 as default height.
           lpMeasureItemStruct->itemHeight = newHeight ? newHeight : 14;
       }
       CFormView::OnMeasureItem(nIDCtl, lpMeasureItemStruct);
   }

IDC_LIST1 is the ID of the owner-drawn ListView control.

NOTE: This problem does NOT appear on Visual C++ for the Macintosh version 4.0.

REFERENCES
==========

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


Additional query words: ownerdrawn ownerdraw CListCtrl list view WLM 4.0 4.1 4.2 owner-draw

======================================================================
Keywords          : kbHWMAC kbVC kbDSupport kbbuglist
Technology        : kbVCsearch kbHWMAC kbOSMAC kbAudDeveloper kbVCXDev400bMac
Version           : MACINTOSH:4.0b
Issue type        : kbprb

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