frombody null

我的webapi:
  public string Post([FromBody]string value)
        {
            // string order = value.ToString();
            /*
             if (value == "8888")
             {
                 return hotel;
             }
             else if(value == null) {
                 return null;
             }
             return hotel;
            // return hotel;
             //return null;
           */

            return value;

        }


我的post winform程序：

            string reqestMsg = "8888";
            string responseMsg = string.Empty;
            byte[] buffer = Encoding.UTF8.GetBytes(reqestMsg);
            string url = textBox2.Text;
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.ContentLength = buffer.Length;

            using (Stream requestStream = request.GetRequestStream())
            {
                requestStream.Write(buffer, 0, buffer.Length);
            }

            HttpWebResponse resonse = (HttpWebResponse)request.GetResponse();
            Stream responseStream = resonse.GetResponseStream();

            using (StreamReader sr = new StreamReader(responseStream))
            {
                responseMsg = sr.ReadToEnd();
            
                textBox1.Text = responseMsg;
            }

            resonse.Close();
        }
//textbox2.text = "http://localhost:50828/api/gethotellist/";

这个样子，但是传递过去的返回值 一直为NULL，就是传递参数 赋值不了value~求救！！！！