asp.net异步上传

<script src="~/Scripts/MyAjaxForm.js"></script>
 
 @using (Ajax.BeginForm("AjaxAddUserPrintReport", "Admin", new AjaxOptions() { HttpMethod = "post", LoadingElementId = "loading", OnSuccess = "afterOk",OnFailure="afterErr" }, new { id = "addform", @class = "form-horizontal", enctype = "multipart/form-data" }))
    {

<div class="form-group">
            <label for="uploadfile" class="col-md-2 control-label">  上传文件：</label>
            <div class="col-md-4">
                <textarea class="form-control hidden" id="Uploadfileurl" name="Uploadfileurl" rows="3"></textarea>
                <input type="file" id="fileup" name="fileup" />
                <button type="button" id="btnupload" class="btn btn-warning btn-sm">上传</button>
            </div>
            <div id="showfile" class="col-md-4">

            </div>
        </div>
}

  //点击上传文件
        $("#btnupload").click(function () {
            if ($(":file").val() == "")
            {
                alert("请选择上传文件后再点击上传按钮");
                return;
            }
            $("#addform").ajaxSubmit({
                error: function (error) { alert(error); },
                url: ‘/Admin/AjaxUploadFile‘,
                type: "post",
                success: function (data) {
                    var arr = data.split(":");
                    if (arr[0] == "ok") {
                        $("#Uploadfileurl").val($("#Uploadfileurl").val().trim()==""?arr[1]: $("#Uploadfileurl").val()+ "," + arr[1]);
                        addfile();
                    }
                    else {
                        alert(arr[1]);
                    }
                }                
            });
        });

 /// <summary>
        /// 上传文件，最大上传10M
        /// </summary>
        /// <returns></returns> 

public ActionResult AjaxUploadFile()
        {
            try
            {
                HttpPostedFileBase uploadfile = Request.Files["fileup"];
                if (uploadfile == null)
                {
                    return Content("no:非法上传");
                }
                if (uploadfile.FileName == "")
                {
                    return Content("no:请选择文件");
                }
                if (uploadfile.ContentLength > 10 * 1024 * 1024)
                {
                    return Content("no:上传文件超过10M，实际上传大小为" + uploadfile.ContentLength);
                }
                string filename = Path.GetFileName(uploadfile.FileName);
                string fileExt = Path.GetExtension(filename);
                StringBuilder sbtime = new StringBuilder();
                sbtime.Append(DateTime.Now.Year).Append(DateTime.Now.Month).Append(DateTime.Now.Day).Append(DateTime.Now.Hour).Append(DateTime.Now.Minute).Append(DateTime.Now.Second);
                string dir = "/UploadFile/" + getUserBySession().Name + "/"  + filename.Substring(0, filename.LastIndexOf(".")) + "_" + sbtime.ToString() + fileExt;
                string realfilepath = Request.MapPath(dir);
                string readDir = Path.GetDirectoryName(realfilepath);
                if (!Directory.Exists(readDir))
                    Directory.CreateDirectory(readDir);

                uploadfile.SaveAs(realfilepath);
                return Content("ok:" + dir);
            }
            catch (Exception ex)
            {
                return Content("no:" + ex.Message);
            }