c#进行http请求

这个函数可以解决中文上传问题

        private string HttpPostNew(string Url,string postDataStr) 
        {
            //string post_string = Encoding.UTF8.GetString(Encoding.UTF8.GetBytes(postDataStr));
            byte[] postBytes = Encoding.GetEncoding("utf-8").GetBytes(postDataStr);
            HttpWebRequest request = WebRequest.Create(Url) as HttpWebRequest;//(HttpWebRequest)WebRequest.Create(Url);
            request.Method = "POST";
            //request.ContentType = "application/x-www-form-urlencoded";
            request.ContentType = "application/json";
            
            request.ContentLength = postBytes.Length;//Encoding.UTF8.GetByteCount(post_string);
            // request.CookieContainer = cookie;

            Stream myRequestStream = request.GetRequestStream();
            //StreamWriter myStreamWriter = new StreamWriter(myRequestStream, Encoding.GetEncoding("utf-8"));           
            //myStreamWriter.Write(post_string);
            //myStreamWriter.Close();


            myRequestStream.Write(postBytes, 0, postBytes.Length);
            myRequestStream.Close();

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            //response.Cookies = cookie.GetCookies(response.ResponseUri);
            Stream myResponseStream = response.GetResponseStream();
            StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));
            string retString = myStreamReader.ReadToEnd();
            myStreamReader.Close();
            myResponseStream.Close();

            return retString;
        }

以下函数不能解决中文上传问题，如果上传的数据里有中文，写入的时候就会出错：

        private string HttpPost(string Url, string postDataStr)
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);
            request.Method = "POST";
            request.ContentType = "application/json";
            request.ContentLength = Encoding.UTF8.GetByteCount(postDataStr);
            Stream myRequestStream = request.GetRequestStream();
            StreamWriter myStreamWriter = new StreamWriter(myRequestStream, Encoding.GetEncoding("gb2312"));
            myStreamWriter.Write(postDataStr);
            myStreamWriter.Close();
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            Stream myResponseStream = response.GetResponseStream();
            StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));
            string retString = myStreamReader.ReadToEnd();
            myStreamReader.Close();
            myResponseStream.Close();
            return retString;
        }