Re: timer-event in a CDocument-derived class

mfc <>
Thu, 19 Aug 2010 12:25:15 -0700 (PDT)
On 19 Aug., 20:22, Joseph M. Newcomer <> wrote:

See by essay on how to add a timer to a CDocument class, on my MVP Tips s=


Hint: it involves creating a dummy window to handle the timer notificatio=



More below...

On Thu, 19 Aug 2010 08:37:44 -0700 (PDT), mfc <> wr=



using a SDI (single-doc-template) application, is it also possible to
generate a timer-event in a CDocument-derived class (http://

My default document class is:
class CMIAppDoc : public CDocument

For my serial-ports, I need a timer. Therefore I tried to implement a
second class ( CTimedDocument) derived from the CDocument. Do I have
to derived this class from my CMIAppDoc (because of the sdi
restriction to only one document)?

class CSerialWrite : public CWinThread
  CTimedDocument tdoc;
  CTimerWnd wnd;
  void Init(void);

void CSerialWrite::Init(void)
 wnd.Start(3000, &tdoc);

The problem I have is that the virtual method
virtual void OnTimer(){ ASSERT(FALSE); }
failed, because it is not correct declared in my subclass?!?

class CTimedDocument : public CDocument

     virtual void OnTimer(){ ASSERT(FALSE); }

class CSerialTimeDoc : public CTimedDocument
     virtual void OnTimer();

Note that you cannot put an OnTimer handler in a CDocument class. This=

 is because

WM_TIMER messages are only sent to windows, and a document cannot receive=


You cannot override this method. For one thing, if you read the docume=

ntation of OnTimer,

you would have seen it is
        afx_msg void OnTimer(UINT_PTR nIdEvent)
which means that (a) it is member of CWnd, and therefore cannot be in CDo=

cument (b) it is

not virtual, so your declaration of a virtual method is meaningless.

I note that the most critical piece of code, the piece of code where you =

set the timer,

has not been shown, so it is not clear how we are supposed to guess at wh=

at you did, or

why you would expect the OnTimer method to be called.

best regards

Joseph M. Newcomer [MVP]
MVP Tips: Zitierten Text ausblenden =


- Zitierten Text anzeigen -

thanks for your answer. I`m using your CTimerWnd class. In my thread-
class I call the CTimerWnd::Start() method. -> afx_msg OnTimer is
called and doc->OnTimer will take a look if there`s such an method in
the document subclass CSerialTimeDoc because doc is a member of
CTimedDocument. And CTimedDocument has only a virtual void OnTimer()

class CTimedDocument : public CDocument
      virtual void OnTimer(){ ASSERT(FALSE); }

But I always get the ASSERT.

class CSerialTimeDoc : public CTimedDocument
      virtual void OnTimer();

Here`s the start where I create the new window.

BOOL CTimerWnd::Start(UINT ms, CTimedDocument * d)
    interval = ms;
    doc = d;
    return CWnd::Create(NULL, // class name, left MFC invent one
                NULL, // title, meaningless
                WS_CHILD, // child window
            // conspicuous by its absense:
                      // WS_VISIBLE
                CRect(0,0,10,10), // useless nonempty rectangle
                AfxGetMainWnd(), // attach to main window, need someplace
                IDC_STATIC); // window ID

void CTimerWnd::OnTimer(UINT nIDEvent)
 if(doc != NULL)
        doc->OnTimer(); //?!?!? virtual void
OnTimer(void) failed


int CTimerWnd::OnCreate(LPCREATESTRUCT lpCreateStruct)
    if (CWnd::OnCreate(lpCreateStruct) == -1)
        return -1;

        SetTimer(IDT_TIMER, interval, NULL);
    return 0;

best regards

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