asax文件使用

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.SessionState;
using System.Xml.Linq;

namespace WzJyw.asax
{
    public class Onle : System.Web.HttpApplication
    {

        protected void Application_Start(object sender, EventArgs e)
        {
            //在应用程序启动时运行的代码
            Application["online"] = 0;  //初始化在线人数变量值
        }

        protected void Session_Start(object sender, EventArgs e)
        {
            //在新会话启动时运行的代码,新会话开始表示有新的用户加入
            Application.Lock();  //锁定Application
            int NUM = (int)Application["online"] + 1;
            Application.Set("online", NUM); //修改对象值,为自身+1
            Application.UnLock(); //解除对象锁定
        }

        protected void Application_BeginRequest(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)
        {
            //在会话结束时运行的代码
            //注意：只有在Web.config文件中的sessionstate模式设置为
            //Inproc时,才会触发Session_End事件.如果会话模式设置为StateServer
            //或SQLServer,则不会触发该事件
            Application.Lock();  //锁定Application
            int NUM = (int)Application["online"] - 1;
            Application.Set("online", NUM); //修改对象值,为自身+1
            Application.UnLock(); //解除对象锁定
        }

        protected void Application_End(object sender, EventArgs e)
        {

        }
    }
}

我想把在线人数显示在Label上 但是不可以 大家帮忙下 谢谢了
    public partial class Head2 : System.Web.UI.UserControl
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            lblOnle.Text = Application["online"].ToString(); //显示在线人数
            Response.AddHeader("Refresh", "30"); //设置30秒刷新一次
        }
    }