有没有大佬帮忙看一下，小白最近在做导出excel功能的时候遇到一个问题，为什么我前端获取的json字符串数据在发送给后端时，后端接收一直为null 前段代码

function exportBtn() {         var selectedRowIds = $("#gridList").getGridParam("selarrrow");         var rowDataList = [];         for (var i = 0; i < selectedRowIds.length; i++) {             var rowData = $("#gridList").getRowData(selectedRowIds[i]);             rowDataList.push(rowData);         }                  var datajson = JSON.stringify(rowDataList);         var list = JSON.parse(datajson)         PostAndGetFileByUrl("/Baseinfo/JSD_MDLY/Export", "POST", list);     };     function PostAndGetFileByUrl(url, type, postdata) {         var temp;                  $.ajax({             url: url,             type: type,             data: { jsondata: postdata },             datatype: "",             success: function (data) {                 downloadFile(data);             }         });         return temp;     }

    function downloadFile(url) {         try {             var elemIF = document.createElement("iframe");             elemIF.src = url;             elemIF.style.display = "none";             document.body.appendChild(elemIF);         } catch (e) {

        }     }

后端代码

public ActionResult Export(string jsondata)         {             System.Diagnostics.Debug.WriteLine(jsondata);             string listjsonstr =@"{ ""rows"":"+jsondata+ " }";            

            DataTable dt = new DataTable();

            dt.Columns.Add("付款单号");             。。。。。。。。。。。

                        JObject json1 = (JObject)JsonConvert.DeserializeObject(listjsonstr);             JArray array = (JArray)json1["rows"];  

           foreach (var jObject in array)             {                 //赋值属性                                DataRow dr = dt.NewRow();                 dr["付款单号"] = jObject["ZFKDH_G"].ToString();                 。。。。。。。。。。。。。。。。

                dt.Rows.Add(dr);//获取字符串中id值                        }

            NPOIExcel npoiexel = new NPOIExcel();             string fileDir = DateTime.Now.ToString("yyyyMMdd");             string fileName = "门店联营.xls";             string destDir = Server.MapPath(@"/XlsTemp") + "\\" + fileDir + "\\";             if (!Directory.Exists(destDir))             {                 Directory.CreateDirectory(destDir);             }

            npoiexel.ToExcel(dt, "门店经销结算数据", "Sheet1", destDir + fileName);             return Content("/XlsTemp/" + fileDir + "/" + fileName);

        }