.Net定时弹出窗口(c#)

using System;
using System.Collections;
using System.ComponentModel;
using System.Web;
using System.Web.SessionState;
using System.Threading;
using System.Timers;

namespace PopUp
{
 public class Global : System.Web.HttpApplication
 {
  private System.ComponentModel.IContainer components = null;
  private System.Timers.Timer aTimer;
            public static DateTime dtBegin;
  public static long TimeInterval=10000;
  public static bool TimeOut;

public Global()
  {
   InitializeComponent();
  } 
  
  protected void Application_Start(Object sender, EventArgs e)
  {
   TimeOut=false;
   dtBegin=DateTime.Now;
   aTimer = new System.Timers.Timer();
   aTimer.Elapsed+=new ElapsedEventHandler(OnTimedEvent);
   aTimer.Interval=TimeInterval;
   aTimer.Enabled=true;
  }
 
  protected void Session_Start(Object sender, EventArgs e)
  {
  }

protected void Application_BeginRequest(Object sender, EventArgs e)
  {
        if (TimeOut==true)
   {
   TimeSpan ts=DateTime.Now-dtBegin;
                  string str="<script>alert('You have been in this application ";
   str=str+ts.Hours+" hours "+ts.Minutes +" minutes "+ts.Seconds +" seconds!')</script>";
   Response.Write(str);
   TimeOut=false;
   }
  }

protected void Application_EndRequest(Object sender, EventArgs e)
  {
  }

protected void Application_AuthenticateRequest(Object sender, EventArgs e)
  {
  }

protected void Application_Error(Object sender, EventArgs e)
  {

}

protected void Session_End(Object sender, EventArgs e)
  {
  }

protected void Application_End(Object sender, EventArgs e)
  {
   this.aTimer.Enabled=false; 
  }

private void OnTimedEvent(object source, ElapsedEventArgs e)
  {
   TimeOut=true;
  }
   
  #region Web Form Designer generated code
  private void InitializeComponent()
  {   
  }
  #endregion
 }
}