Asp.Net - 如何使Cookie失效

Question

尝试

 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;

并尝试通过评论未注释的代码并取消注释注释代码，但

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

始终在线，Request.Cookies["IsGuest"]永远不会null

Answer 1

你有一个以编程方式删除cookie的正确概念：

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

然而，你错过了一点。的 The above change wonn't be effective until the postback completes and subsequently user initiates a new request

MSDN 说：

<强> 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"); 
            cookie.Expires = DateTime.Now.AddDays(-1d); 
            Response.Cookies.Add(cookie);
        }

        // 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!";                
        }
    }

最后一个注意事项::

调用Cookies集合的Remove方法会删除服务器端的cookie，因此cookie不会发送到客户端。但是，如果cookie已经存在，则该方法不会从客户端中删除cookie。

Answer 2

最好从列表中删除Cookie