HttpCookie userinfoCookie = new HttpCookie("userinfo");
JObject o = new JObject();//JObject是Newtonsoft.Json.Linq中的对象
o["userid"] = userDB.UserID.ToString();
o["nickname"] = userDB.NickName;
o["avatar"] = userDB.ImageUrl;
userinfoCookie.Value = o.ToString();
Response.Cookies.Add(userinfoCookie);