使用Ajax BeginForm HttpPostedFileBase上传文件时出错始终为null

Question

我使用Ajax.Beginform menthod上传文件，但它不起作用，请帮帮我。

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" />
        }

服务器端的控制器

[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 });
    }

参数fileupload alway null，我引用了很多帖子但仍然没有解决问题：（

抱歉，我的英语非常糟糕