Asp.Net_单点登录

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (Application["UsName"] != null)
{
Response.Write("记录的用户名：" + Application["UsName"]);
}
}
/// <summary>
/// 登录
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
protected void OnloginbtnClick(object sender, EventArgs e)
{
if (txt_UsName.Text.Length > 0 && txt_UsPwd.Text.Length > 0)
{
if (Application["UsName"] != null)
{
//判断用户是否已经登录过
string[] UsNameArray=Application["UsName"].ToString().Split(',');
for (int i = 0; i < UsNameArray.Length; i++)
{
if (UsNameArray[i] == txt_UsName.Text.Trim())
{
Response.Write("<script>alert('你已经登录!');</script>");
return;
}
}
}
string strSplit = "";
Session["loginUsName"] = txt_UsName.Text.Trim();
Application.Lock();
if (Application["UsName"] != null)
{
strSplit = ",";
}
Application["UsName"] = Application["UsName"] + strSplit + Session["loginUsName"].ToString();
Application.UnLock();

Response.Write("<script>alert('成功登录!');</script>");
}
else
{
Response.Write("<script>alert('请填写用户名和密码!');</script>");
}
}

/// <summary>
/// 退出登录
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
protected void OnSignOutBtnClick(object sender, EventArgs e)
{
if (Session["loginUsName"] != null)
{
Application.Lock();
Application["UsName"] = Application["UsName"].ToString().Replace(Session["loginUsName"].ToString(), "");
Application.UnLock();
Response.Write("<script>alert('" + Session["loginUsName"] + "已经成功退出" + "!');</script>");
}
}
}

{
//在应用程序启动时运行的代码
Application["UsName"] = null;

}