文档文件由ajax上传到控制器但是变为空

Question

我想通过ajax将文件上传到controller.But在控制器方法参数中获取null。 控制器

public ActionResult Upload(HttpPostedFileBase file,int value)
{
    try
    {
        if (file.ContentLength > 0)
        {
            var fileName = Path.GetFileName(file.FileName);
            var path = Path.Combine(Server.MapPath("~/File/"), fileName);
            file.SaveAs(path);
            _manager.UploadFile(file, path.ToString());
        }
        ViewBag.Message = "Upload successful";
        return RedirectToAction("Index");
    }
    catch
    {
        ViewBag.Message = "Upload failed";
        return RedirectToAction("Index");
    }
}

在索引中我正在使用普通的输入文件类型并提交类型按钮。一切正常但控制器方法参数变为空为什么？

索引

<label class="btn btn-block btn-primary">
    Browse &hellip;
    <input type="file" name="file" class="btn" id="uploadfile" style="display: none;">
</label>
<input type="submit" class="btn" id="submit" value="Upload">

$(document).ready(function (e) {
    $('#submit').click(function (event) {
        var formData = new FormData();
        var totalfiles = document.getElementById("uploadfile");
        for (var i = 0; i < totalfiles; i++) {
            var file = document.getElementById("uploadfile").files[i];
            formData.append("uploadfile", file);
        }
        var dam=1;
        dam = $("input:checkbox:checked").attr("value");
        alert(dam);
        alert(formData);
        $.ajax(
        {
            url: '@Url.Action("Upload","Document")',
            type: "POST",
            data: { file: formData ,value:dam},
            datatype: "multipart/form-data",
            traditional: true,
            success: function (response) {
                // $("#file").html(response);
            }
        });
    })
});