系统对象的使用——Cookie，ViewState，Session，Application

Cookie

 //将数据保存到Cookie
        //Cookie是一个字典
        //如果没有指定Cookie的保存时间，则这个Cookie是临时Cookie
        //临时Cookie只要浏览器一关闭，就取消
        //Response.Cookies["account"].Value = txt1.Text;

        //如果指定了Cookie的保存时间，这个Cookie就叫持久Cookie
        Response.Cookies["account"].Value = txt1.Text;
        Response.Cookies["account"].Expires = DateTime.Now.AddMinutes(1);

        //Response.Cookies["account"].Expires = DateTime.Now.AddMinutes(-1);

 if (Request.Cookies["account"] != null)
        {
            lab1.Text = Request.Cookies["account"].Value;
        }

ViewState

利用ViewState保持页面状态_页面状态对象

protectedvoid btn3_Click(object sender, EventArgs e)

    {

        a = 10;

        b = 20;

        //ViewState是一个字典，键值对

        //ViewState用于本页面回发时保持状态

        ViewState["a"] = a;

        ViewState["b"] = b;

    }

protectedvoid btn4_Click(object sender, EventArgs e)

    {

        a = Convert.ToInt32(ViewState["a"]);

        b = Convert.ToInt32(ViewState["b"]);

        c = a + b;

        lab2.Text = c.ToString();

}

 

Session

Session["username"] = txt1.Text;

if (Session["username"] != null)

        {

            lab1.Text = Session["username"].ToString();

        }

 

Application公共对象

//因为Application对象时公共对象

        //当多个用户同时修改Application对象时，可能会引发不可预知的问题

        //并发

 

        Application.Lock();//锁定对象

        //Application.Add("account", txt1.Text);

        Application["account"] = txt1.Text;

        //...

        Application.UnLock();//解锁对象

 

 

if (Application["account"] != null)

        {

            lab1.Text = Application["account"].ToString();

        }

 

  //ViewState是一个字典，键值对
        //ViewState用于本页面回发时保持状态
        ViewState["a"] = a;
        ViewState["b"] = b;