Asp.Net - 如何使 Cookie 过期

Question

试过了

 if (Request.Cookies["IsGuest"] != null)
     {
       Response.Cookies["IsGuest"].Expires = DateTime.Now.AddDays(-1);
       //HttpCookie myCookie = new HttpCookie("IsGuest");
       //myCookie.Expires = DateTime.Now.AddDays(-1d);
       //Response.Cookies.Add(myCookie);
     }
    string a = Request.Cookies["IsGuest"].Value;

还尝试通过注释未注释的代码和取消注释已注释的代码来尝试，但是

 string a = Request.Cookies["IsGuest"].Value;

一直在运行，Request.Cookies["IsGuest"] 永远不是null

Answer 1

您了解了以编程方式删除 cookie 的正确概念：

HttpCookie myCookie = new HttpCookie("IsGuest"); 
cookie.Expires = DateTime.Now.AddDays(-1d); 
Response.Cookies.Add(cookie);

但是，您错过了一分。 The above change won't be effective until the postback completes and subsequently user initiates a new request。

MSDN 说：

The next time a user makes a request to a page within the domain or path that set the cookie, the browser will determine that the cookie has expired and remove it.

所以，下面的代码在这里说明了更多：：

protected void DeleteCookie_ButtonClick(object sender, EventArgs e)
    {
        if (Request.Cookies["IsGuest"] != null)
        {
            HttpCookie myCookie = new HttpCookie("IsGuest"); 
            myCookie.Expires = DateTime.Now.AddDays(-1d); 
            Response.Cookies.Add(myCookie);
        }
        
        // this will always be true here as the Request  i.e HttpRequest isn't 
        // modified actually as the postback isn't complete and we are accessing 
        // the Cookies collection of same request (not a new request)
        if (Request.Cookies["IsGuest"] != null)
        {
            Label1.Text = "Cookie Collection  can't be modified without 
                           making a new request";
        }

    }
    
   // suppose after postback completes, 
   // user clicks a buttonn to check the cookie, 
   // which in turn is a new request/postback/....
    protected void CheckCookie_ButtonClick(object sender, EventArgs e)
    {
        if (Request.Cookies["IsGuest"] != null)
        {
            Label1.Text = "Cookie is present!";                
        }
        else
        {
            Label1.Text = "No Cookie is present!";                
        }
    }

最后一点：

调用 Cookies 集合的Remove 方法会移除服务器端的 cookie，因此不会将 cookie 发送到客户端。但是，如果 cookie 已经存在，该方法不会从客户端删除它。

Answer 2

最好从列表中删除 cookie