HOWTO: Create a Timed MessageBox

• Microsoft Win32 Software Development Kit (SDK)

SUMMARY

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

MORE INFORMATION

Normally, when you need to display a message box for a limited amount of time, you must implement a regular dialog box that destroys 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 example below shows how to use the MessageBox API to create a message box that automatically terminates after a specified amount of time. 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 that the WM_QUIT message must be removed from the message queue to prevent it from being retrieved in the main message queue.

Sample Code

   /***********************************************************************
      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. Since the
    *      message loop for a message box is part of USER, you cannot
    *      modify it.
    *
    *      However, all message loops exit when they receive a
    *      WM_QUIT message. Furthermore, a nested message loop, if it
    *      receives a WM_QUIT message, must break the loop and then re-post
    *      the quit message so that the next outer layer can process it.
    *
    *      Therefore, you can get the nested message loop to exit by
    *      calling PostQuitMessage(). 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,
    *      then 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 running.
    *
    *      Essentially, you have "tricked" the nested message loop into
    *      thinking that the application is terminating. When it returns,
    *      you "eat" the quit message, effectively canceling the fake
    *      quit that you generated.
    *
    **********************************************************************/

   /**********************************************************************
    *
    *  MessageBoxTimer
    *
    *      The timer callback function that posts the fake quit message,
    *      which causes the message box to exit because it thinks that
    *      the application is exiting.
    *

    **********************************************************************/

   void CALLBACK
   MessageBoxTimer(HWND hwnd, UINT uiMsg, UINT idEvent, DWORD dwTime)
   {
       PostQuitMessage(0);
   }

   /***********************************************************************
    *
    *  TimedMessageBox
    *
    *      The same as the standard MessageBox, except it also accepts
    *      a timeout. If the user does not respond within the
    *      specified timeout, then the value 0 is returned instead
    *      of one of the ID* values.
    *
    **********************************************************************/

   UINT
   TimedMessageBox(
       HWND hwndParent,
       LPCTSTR ptszMessage,
       LPCTSTR ptszTitle,
       UINT flags,
       DWORD dwTimeout)
   {
       UINT idTimer;
       UINT uiResult;
       MSG msg;

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

       uiResult = MessageBox(hwndParent, ptszMessage, ptszTitle, flags);

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

       /*
        *  See if there is a WM_QUIT message in the queue. If so,
        *  then you timed out. Eat the message so you don't quit the
        *  entire application.
        */
       if (PeekMessage(&msg, NULL, WM_QUIT, WM_QUIT, PM_REMOVE)) {

           /*
            *  If you timed out, then return zero.
            */
           uiResult = 0;
       }

       return uiResult;
   }

   /***********************************************************************
    *
    *  WinMain
    *
    *      Program entry point.
    *
    *      Demonstrate TimedMessageBox().
    *
    **********************************************************************/

   int WINAPI
   WinMain(
       HINSTANCE hinst,
       HINSTANCE hinstPrev,
       LPSTR pszCmdLine,
       int nCmdShow)
   {

       UINT uiResult;

       /*
        *  Ask the user a question, and give him or her five seconds to
        *  answer it.
        */

       uiResult = TimedMessageBox(NULL, "Does a triangle have three
                                         sides?",
                                  "Quiz", MB_YESNO, 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 0:
           MessageBox(NULL, "I sensed some hesitation there.  "
                            "The correct answer is Yes.", "Result", MB_OK);
           break;
       }

       return 0;
   }