虽然不常用，不过还是要记录一下。
以后要多学会用Cookie保存用户信息。

  public void SaveCookie()
    {
        // Use this line when you want to save a cookie
        Response.Cookies["MyCookieName"].Value = "MyCookieValue";
        // How long will cookie exist on client hard disk
        Response.Cookies["MyCookieName"].Expires = DateTime.Now.AddDays(1);

        // To add multiple key/value pairs in single cookie
        Response.Cookies["VisitorData"]["FirstName"] = "Richard";
        Response.Cookies["VisitorData"]["LastVisit"] = DateTime.Now.ToString();
    }

    public void ReadCookie()
    {
        string MyCookieValue;
        // We need to perform this check first, to avoid null exception
        // if cookie not exists
        if (Request.Cookies["MyCookieName"] != null)
            MyCookieValue = Request.Cookies["MyCookieName"].Value;
    }

    public void ClearCookie()
    {
        // First check if cookie exists
        if (Request.Cookies["MyCookieName"] != null)
        {
            // Set its expiration time somewhere in the past
            Response.Cookies["MyCookieName"].Expires = DateTime.Now.AddDays(-1);
        }
    }