统计在线人数

<%@ Import Namespace="System.Data"%>
void Application_Start(object sender, EventArgs e) 
    {
       //在应用程序启动时运行的代码,网站启动时即出发此事件
        try
        {

            DataTable userTable = new DataTable();
            userTable.Columns.Add("SessionID");
            userTable.Columns.Add("UserIP");
            userTable.Columns.Add("Browser");
            userTable.Columns.Add("OSName");

            userTable.AcceptChanges();
            Application.Lock();
            Application["OnLineusers"] = userTable;
            Application.UnLock();
    }

    void Session_Start(object sender, EventArgs e) 
    {
        //在新会话启动时运行的代码，用户访问时会触发Session_Start事件，在Session_Start中记录下该用户的信息，存入表中,
        //Application["OnLineusers"]存放了所有用户的信息

        string sessionid = Session.SessionID;
        string userIP = Request.UserHostAddress;
        HttpBrowserCapabilities bc = Request.Browser;
        string osName = bc.Platform;
        string Browser=bc.Type;

        DataTable userTable = (DataTable)Application["OnLineusers"];
        if (userTable == null) return;
        DataRow[] curRow=userTable.Select("SessionId='"+sessionid+"'");
        if (curRow.Length == 0)
        {
            DataRow newRow = userTable.NewRow();
            newRow["SessionID"] = sessionid;
            newRow[1] = userIP;
            newRow[2] = Browser;
            newRow[3] = osName;
            userTable.Rows.Add(newRow);
            userTable.AcceptChanges();
            Application.Lock();
            Application["OnLineusers"] = userTable;
            Application.UnLock();
             
        }
        
      }

   //移除回话结束的Session
　　void Session_End(object sender, EventArgs e)
    {
        Hashtable onlineuserhash = (Hashtable)Application["OnLineusers"];
        onlineuserhash.Remove(Request.UserHostAddress);

        string sessionid = Session.SessionID;
        DataTable usertable = (DataTable)Application["OnLineusers"];
        if (usertable == null)
        { return; }
        foreach (DataRow row in usertable.Select("SessionID='" + sessionid + "'")) 
        {
            usertable.Rows.Remove(row); 
        }
        usertable.AcceptChanges();
        Application.Lock();
        Application["OnLineusers"] = usertable;
        Application.UnLock();
    }

 常用的解决方法：在项目下建一个txt文件存储在线人数,Session_Start,Session_end对txt进行操作