使用Ajax上传文件时出错。HttpPostFileBase始终为空

我使用Ajax.Beginform方法上传文件，但它不工作，请帮助我

文件Create.cshtml：

@using (Ajax.BeginForm("UpLoadFile", "KG", new AjaxOptions { HttpMethod = "POST" }, new { enctype = "multipart/form-data", @id = "form-uploadfile" }))
        { 
            <input type="file" name="fileupload" id="fileupload" />
            <input type="submit" value="UpLoad" />
        }

参数fileupload始终为空，我引用了许多帖子，但仍然解决了问题：(

对不起，我的英语很差

[HttpPost]
    public ActionResult UploadFile(HttpPostedFileBase fileupload)
    {
        if (fileupload != null)
        {

                // Verify that the user selected a file
            if (fileupload != null && fileupload.ContentLength > 0)
                {
                    // extract only the fielname
                    var fileName = Path.GetFileName(fileupload.FileName);
                    // TODO: need to define destination
                    var path = Path.Combine(Server.MapPath("~/Upload"), fileName);
                    fileupload.SaveAs(path);
                }

        }
        return Json(new { success = true });
    }