I am getting 'null' value for HttpPostedBaseFile in controller.I am calling the Action method using jquery through Json.
View code
@using (Html.BeginForm("SaveAlertList", "AlertListUpload", new { enctype = "multipart/form-data" }, FormMethod.Post, new { id = "formUpload" }))
{
    @Html.ValidationSummary(null, new {@class = "validation-summary formErrors ui-state-error invisible"})
    <div class="table-container">
        <div class="table-container-row">
            <div class="table-container-cell">
                <fieldset>
                    <legend id="importlegend"><b>Import</b></legend>
                    <input type="file" id="uploadfile" name="uploadfile" style="width: 370px; height: 22px" />
                </fieldset>
            </div>
        </div>
    </div>
    <div id="AlertListDetails">
        <table id="grdAlertListUpload" style="border-collapse: separate"></table>
    </div>
}
Controller Code
[HttpPost]
    public JsonResult SaveAlertList(HttpPostedFileBase uploadfile)
    {
        string message1 = string.Empty;
        HttpPostedFileBase file = Request.Files["uploadfile"];
        try
        {
            if (uploadfile != null && uploadfile.ContentLength != 0)
            {
                var fileName = Path.GetFileName(uploadfile.FileName);
                if (fileName !=null)
                {
                    var path = Path.Combine(Server.MapPath(UploadFolderPath), fileName);
                    uploadfile.SaveAs(path);
                }
                message1 = ConfirmationMessages.AlertListUploadComplete;
            }
            return Json(new { Result = "OK", Message1 = message1 });
        }
        catch(Exception ex)
        {
            LoggerService.Logger.Log(ex);
            return Json(new { Result = "ERROR", Message1 = ex.Message });
        }
    }
Here is the jquery code
$("#btnUpload").on('click', function () {
  loadingDialog.show("Saving data..."); 
  performJsonCall(AlertListUpload.SaveAlertList, 'json', "", function(data) { 
    AlertListUpload.SaveSuccess(data);
  });
});
Any help is appreciated.
