layui upload 后台获取不到值

后台获取不到值方法一：

<script>

    layui.use('upload', function () {

        var upload = layui.upload;

        //执行实例

        var uploadInst = upload.render({

            elem: '#test1' //绑定元素

            , url: '/Home/UploadFiles' //上传接口

             , field: "fileNames"     //添加这个属性与后台名称保存一致

            , accept: 'file' //允许上传的文件类型

            , size:  //最大允许上传的文件大小

            , before: function (obj) { //obj参数包含的信息，跟 choose回调完全一致，可参见上文。

                layer.load(); //上传loading

            }

            , done: function (res) {

                //上传完毕回调

                alert(res.tc);

            }

            , error: function () {

                //请求异常回调

            }

        });

    });

</script>

 public ActionResult UploadFiles(HttpPostedFileBase fileNames)

        {

            string path = "";

            //小于20M

            if (fileNames.ContentLength >  && fileNames.ContentLength <= )

            {

                var fileName = Path.GetFileName(fileNames.FileName);

                string q_FN = fileName.Substring(, fileName.LastIndexOf("."));

                string h_FN = fileName.Substring(fileName.LastIndexOf("."));

                string NewFileName = q_FN + DateTime.Now.ToString("yyyyMMddHHmmss") + h_FN;

                path = Path.Combine(Server.MapPath("/Uploadfile/"), NewFileName);

                fileNames.SaveAs(path);

                path = "/Uploadfile/" + NewFileName;

                var relt = new { tc = path };

                return Content(JsonConvert.SerializeObject(relt));

            }

            else

            {

                var relt = new { tc = "上传文件要小于20M" };

                return Content(JsonConvert.SerializeObject(relt));

            }

        }