A thread-safe timed message box

• Download demo project - 17 Kb
• Download source - 3 Kb

What is the code for

This is for using the systems MessageBox (no extra dialog creation needed). After a time with no user-response the dialog is automatically closed. An optional text showing the time left to interact is provided. It's also a replacement for MSDN Q181934 (doesn't work)

Basics

Before calling MessageBox, a timer is installed. In the timer's callback-procedure the message-text from the box is replaced (optional).

When the box should be closed, a WM_COMMAND is posted to the MessageBox Window.

Timer-Callback

I decided to collect all the information corresponding to the MessageBox (title, Message, Flags ...) in a class. Then there is the problem that only a static timer-callback-procedure can be installed with the SetTimer()-function: one can not access the class-members (as it is static).

To solve this problem, I inserted a Map to store the classes corresponding to a timer-id:

Header:

class CDlgTimedMessageBox
{
public:
    // ...

    UINT         ShowMessageBox(BOOL *pbStoppedByUser=NULL);
    // ...

    static void  CALLBACK GlobalTimerProc(HWND hwnd, UINT uiMsg, 
                                          UINT idEvent, DWORD dwTime);
    void         LocalTimerProc(void);
    // ...

    static       CMapPtrToPtr        m_mapTimerIdToClassMe;

    // to call the messagebox within one line !

    static UINT  TimedMessageBox(...);

protected:
    UINT         m_idTimer;
};

Source:

UINT CDlgTimedMessageBox::ShowMessageBox(BOOL *pbStoppedByUser)
{
    // ...

    m_idTimer = ::SetTimer(NULL, 0, 1000, 
                    (TIMERPROC) CDlgTimedMessageBox::GlobalTimerProc);
    CDlgTimedMessageBox::m_mapTimerIdToClassMe.SetAt((void*)m_idTimer, 
                                                     this);
    // ...

    ::MessageBox(...)
    // ...

}

void CALLBACK CDlgTimedMessageBox::GlobalTimerProc(HWND hwnd, 
                               UINT uiMsg, UINT idEvent, DWORD dwTime)
{
    CDlgTimedMessageBox    *pMe = NULL;
    
    // Find the corresponding class by the timer-id

    CDlgTimedMessageBox::m_mapTimerIdToClassMe.Lookup((void*)idEvent, 
                                                       (void *&) pMe);
    
    if( pMe!=NULL )
        pMe->LocalTimerProc();
}

void CDlgTimedMessageBox::LocalTimerProc(void)
{
    // find the Message-Box-window


    // Calculate time since start

    
    if( too long running )
    {
        // Stop MessageBox

    }
    else
    {
        // replace text of MessageBox    

    }    
}

Finding the MessageBox

hWnd = ::GetWindow(::GetDesktopWindow(), GW_CHILD);
while( (hWnd!=NULL) && (m_hMsgBox==NULL) )
{
    pWnd = CWnd::FromHandle(hWnd);
    pWnd->GetWindowText(title);

    if( AfxIsDescendant(m_hParent, hWnd) && ::IsWindowVisible(hWnd) && 
        (m_Title.CompareNoCase(title)==0) )
    {
        m_hMsgBox = hWnd;
        break;
    }
    
    hWnd = ::GetWindow(hWnd, GW_HWNDNEXT);
}

Put it in one function

There is one function you can use to call the messagebox without creating a class-instance: CDlgTimedMessageBox::TimedMessageBox() does the rest for you!

UINT CDlgTimedMessageBox::TimedMessageBox(UINT flags, LPCTSTR ptszMessage, 
                          LPCTSTR ptszTitle, 
                          DWORD dwTimeout, UINT dDefaultReturn,
                          LPCTSTR ptszMessageTimer, HWND hwndParent, 
                          BOOL *pbStoppedByUser)
{
    CDlgTimedMessageBox    msgBox(flags, ptszMessage, ptszTitle, 
                                  dwTimeout, dDefaultReturn, 
                                  ptszMessageTimer, hwndParent);

    return msgBox.ShowMessageBox(pbStoppedByUser);
}

You can pass a BOOL * to get the info, if the user has pressed a button.

Thread-Safe

The map-access is enclosed by a CCriticalSection.

Sample

BOOL	stoppedByUser;
UINT	erg;

erg  = CDlgTimedMessageBox::TimedMessageBox(MB_YESNO|MB_ICONHAND, 
		"Please press a button", 
		"box-title", 
		5000, IDYES, 
		"\nin the next %lu sec !", 
		NULL, &stoppedByUser);

History

5.11.2000     posted to Code Project
14.11.2000   bugfixes for NT4
05.02.2001   bug reported when created with MBYES: defbutton then is IDCANCEL
05.02.2001   global function went to class-scope