将文件上载数据从AngularJS发送到C＃后端

Question

我尝试上传文件并希望将上传文件数据发送到C＃后端。有了这段代码：

HTML

<input type="file" id="upload" name="file" onchange="angular.element(this).scope().uploadedFile(this)" multiple />

AngularJS Serivce

uploadfile: function (files, type, status) {
    var route = 'api/sc/ir/cid/' + $cookies.get("cid") + '/type/' + type + '/status/' + status;
    for (var i = 0; i < files.length; i++) {
      $http.post(serviceBase + route, files[i], {
        withCredentials: false,
        transformRequest: angular.identity,
        headers: { 'Content-Type': 'application/json' }
      })
    }
    return true;
  }

C＃Controller

    [HttpPost]
    [Route("api/sc/ir/cid/{cid:int}/type/{type}/status/{status}")]
    [ResponseType(typeof(ValidateModel))]
    public IHttpActionResult AddFileRequests(int cid, string type, string status, HttpPostedFileBase file)
    {
        var newRequest = logic.UploadDocument(clinicId, type, status, file);
        return Created(Request.RequestUri.ToString(), newRequest);
    }

问题在于＆＃39;文件＆＃39;到达后端时，object为null，但它在前端很好地填充了。我错过了什么？