C# post json 匿名類 序列化

//第一步 創建HTTP請求對象
            var httpWebRequest = (HttpWebRequest)WebRequest.Create(apiURL);
            httpWebRequest.ContentType = "application/json";
            httpWebRequest.Method = "POST";
            

            //第二步 生產請求報文
            var requestObject = new { 
                method="Query"
                ,senderId=senderId
                ,serviceId=serviceId
                ,userCardId=userCardId
                ,userCertId=userCertId
                ,userDept=userDept
                ,userName=userName
                ,
                
                param= new {
                    DataObjectCode = "NNNN"
                    ,Condition="SFZH='11223344'"
                    ,RequiredItems="[\"XM\",\"SFZH\"]"
                    ,InfoCodeMode="1"
                }          
            };

            JavaScriptSerializer js = new JavaScriptSerializer();
            
            string jsonData = js.Serialize(requestObject);

            //params是C#關鍵字，因此最後代替一下解決。
            //'\'單引號在json序列化時會被譯爲unicode編碼，最後解碼便可。

            textBox1.Text =jsonData= Regex.Unescape(jsonData.Replace("param", "params"));

            //DataContractJsonSerializer 序列化JSON須要顯式定義類，且須要標記類成員屬性，比較麻煩暫不用了
            //DataContractJsonSerializer dj = new DataContractJsonSerializer(requestObject.GetType());            
            //MemoryStream msObj = new MemoryStream();
            //dj.WriteObject(msObj, requestObject);
            //textBox1.AppendText("\n" + msObj.ToString());
            try
            {
                //第三步 發送請求
                using (var streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
                {
                    streamWriter.Write(jsonData);
                    streamWriter.Flush();
                    streamWriter.Close();
                }

                //第四步 獲得返回報文
                var httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();
                using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
                {
                    var resualt = streamReader.ReadToEnd();
                    textBox2.Text = resualt;
                }
            }
            catch (Exception ex) {
                textBox2.Text = ex.Message;
            }