Q200054: PRB: OnTimer() Is Not Called Repeatedly for a List Control

Article: Q200054
Product(s): Microsoft C Compiler
Version(s): winnt:4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbListView kbMFC kbTimer kbGrpDSMFCATL
Last Modified: 03-MAY-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), included with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

If you call the SetTimer function to send periodic WM_TIMER messages to a list
control, you may find that the WM_TIMER message handler (the OnTimer function)
for a list control is called only twice.

CAUSE
=====

The WM_TIMER handler in the list control calls the KillTimer function.

RESOLUTION
==========

If you define the timer ID in the SetTimer call, do not call the default handler
for WM_TIMER.

STATUS
======

This behavior is by design.

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

The list control uses the timer for editing labels, and for scrolling. When you
handle the timer message, if the timer ID is your own timer, don't call the
default handler (CListCtrl::OnTimer).

In the sample code below, without the if clause in the CMyListCtrl::OnTimer
function, the default WM_TIMER handler is always called, which destroys both the
control's timer and your own timer. As a result, you should see a trace
statement for each timer.

  void CGensdiView::OnInitialUpdate() 
  {
     CView::OnInitialUpdate();
  	
     m_pCtrl = new CMyListCtrl;
     m_pCtrl->Create(WS_VISIBLE | WS_CHILD | WS_BORDER 
                     | LVS_REPORT | LVS_EDITLABELS, 
                     CRect(0, 0, 100, 150), this, 2134);

     m_pCtrl->InsertColumn(0, "one");
     m_pCtrl->InsertItem(0, "0 0 0 0 0 0 0 0 0 0 0");
     m_pCtrl->InsertItem(1, "1 1 1 1 1 1 1 1 1 1 1");
     m_pCtrl->InsertItem(2, "2 2 2 2 2 2 2 2 2 2 2");
  }

  void CGensdiView::OnLButtonDown(UINT nFlags, CPoint point) 
  {
     m_pCtrl->m_timerID = m_pCtrl->SetTimer(14, 500, NULL);
     TRACE("timer %d is set\n", m_pCtrl->m_timerID);
  }

  CMyListCtrl::CMyListCtrl()
  {
     m_timerID = -1;
  }

  void CMyListCtrl::OnTimer(UINT nIDEvent)
  {
     if (nIDEvent != m_timerID)
        CListCtrl::OnTimer(nIDEvent);
     TRACE("OnTimer %d\n", nIDEvent);
  }

Additional query words: CListview CListctrl WM_TIMER OnTimer KillTimer SetTimer once

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Keywords          : kbListView kbMFC kbTimer kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:4.2,5.0,6.0
Issue type        : kbprb

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