How to create a timed message box

INTRODUCTION

This article explains how to create a timed a message box that is displayed for a limited amount of time and then is automatically dismissed without any user intervention.

More Information

Generally, when you want to display a message box for a limited amount of time, you must implement a regular dialog box that closes itself after a specified amount of time. The problem with this method is that you lose the standard message box functionality that Windows provides.


The following example shows how to use the MessageBox function to create a message box that automatically closes after a specified amount of time. Note the following about the example:
  • The example uses a Windows timer that fires an event after the specified amount of time has elapsed.
  • When the timer event occurs, the PostQuitMessage API is used to break out of the modal message loop that MessageBox uses.
  • Note The WM_QUIT message must be removed from the message queue to prevent it from being retrieved in the main message queue.

Code sample

Note This code sample does not support the use of the MB_SERVICE_NOTIFICATION flag when calling MessageBox from a service. The message box window is not owned by the process calling MessageBox when MB_SERVICE_NOTIFICATION is specified.
/***********************************************************************
THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF
ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A
PARTICULAR PURPOSE.

Copyright 1998 Microsoft Corporation. All Rights Reserved.
***********************************************************************/

/***********************************************************************
*
* MsgBox.c
*
* Abstract:
*
* Sample program to demonstrate how a program can display a
* timed message box.
*
***********************************************************************/

#define STRICT
#include <windows.h>


/***********************************************************************
*
* Overview
*
* The key to creating a timed message box is exiting the dialog
* box message loop internal to the message box. Because the
* message loop for a message box is part of USER, you cannot
* modify the message loop without using hooks and other such methods.
*
*
* However, all message loops exit when they receive a
* WM_QUIT message. Additionally, if a nested message loop
* receives a WM_QUIT message, the nested message loop must break
* the loop and then re-post the quit message so that the next
* outer layer can process it.
*
* Therefore, you can make the nested message loop exit by
* calling the PostQuitMessage function. The nested message loop will
* clean up and post a new quit message. When the MessageBox
* returns, you peek to see if there is a quit message. If so,
* it means that the message loop was abnormally terminated.
* You also consume the WM_QUIT message instead of re-posting it
* so that the application continues to run.
*
* Essentially, you have "tricked" the nested message loop into
* determining that the application is terminating. When the quit message
* returns, you consume the quit message. This method effectively cancels
* the fake quit message that you generated.
*
***********************************************************************/

/***********************************************************************
*
* Global variables
*
***********************************************************************/
HWND g_hwndTimedOwner;
BOOL g_bTimedOut;


/***********************************************************************
*
* MessageBoxTimer
*
* The timer callback function that posts the fake quit message.
* This function causes the message box to exit because the message box
* has determined that the application is exiting.
*
***********************************************************************/
void CALLBACK MessageBoxTimer(HWND hwnd,
UINT uiMsg,
UINT idEvent,
DWORD dwTime)
{
g_bTimedOut = TRUE;
if (g_hwndTimedOwner)
EnableWindow(g_hwndTimedOwner, TRUE);
PostQuitMessage(0);
}


/***********************************************************************
*
* TimedMessageBox
*
* The same as the standard MessageBox, except that TimedMessageBox
* also accepts a timeout. If the user does not respond within the
* specified timeout, the value 0 is returned instead of one of the
* ID* values.
*
***********************************************************************/
int TimedMessageBox(HWND hwndOwner,
LPCTSTR pszMessage,
LPCTSTR pszTitle,
UINT flags,
DWORD dwTimeout)
{
UINT idTimer;
int iResult;

g_hwndTimedOwner = NULL;
g_bTimedOut = FALSE;

if (hwndOwner && IsWindowEnabled(hwndOwner))
g_hwndTimedOwner = hwndOwner;

//
// Set a timer to dismiss the message box.
idTimer = SetTimer(NULL, 0, dwTimeout, (TIMERPROC)MessageBoxTimer);

iResult = MessageBox(hwndOwner, pszMessage, pszTitle, flags);

//
// Finished with the timer.
KillTimer(NULL, idTimer);

//
// See if there is a WM_QUIT message in the queue if we timed out.
// Eat the message so we do not quit the whole application.
if (g_bTimedOut)
{
MSG msg;
PeekMessage(&msg, NULL, WM_QUIT, WM_QUIT, PM_REMOVE);
iResult = -1;
}

return iResult;
}


/***********************************************************************
*
* WinMain
*
* Program entry point. Demonstrate TimedMessageBox().
*
***********************************************************************/
int WINAPI WinMain(HINSTANCE hinst,
HINSTANCE hinstPrev,
LPSTR pszCmdLine,
int nCmdShow)
{

UINT uiResult;

//
// Ask the user a question. Give the user five seconds to
// answer the question.
uiResult = TimedMessageBox(NULL,
"Does a triangle have three sides?",
"Quiz",
MB_YESNO,
// NULL first parameter is important.
5000);


switch (uiResult) {
case IDYES:
MessageBox(NULL,
"That's right!",
"Result",
MB_OK);
break;

case IDNO:
MessageBox(NULL,
"Believe it or not, triangles "
"really do have three sides.",
"Result",
MB_OK);
break;

case -1:
MessageBox(NULL,
"I sensed some hesitation there. "
"The correct answer is Yes.",
"Result",
MB_OK);
break;
}

return 0;
}
Propiedades

Id. de artículo: 181934 - Última revisión: 07/11/2005 - Revisión: 1

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