无法在Angularjs中上传多个文件

Question

您好我正在尝试上传angularjs中的多个文件。我无法上传多个文件，因为它给我错误eferenceError：$ upload未定义 这是我的HTML代码。

<div class="upload-button" ng-repeat="file in files">
                <div class="upload-button-icon">
                    <img src="images/folder-small.png">
                    <div class="upload-text">{{file}}</div>
                    <input type="file" id="file1" name="file1"  />
                </div>
            </div>
  <input type="submit" value="{{ 'NEXT' | translate }}" class="blue-button" ng-click="upload()">

以下是我上传文件的angularjs代码。

  $scope.upload = function () {
                debugger;
                var fileuploadurl = baseurl + 'api/Customer/UploadLeaseFiles/' + LoginID + '/' + "GOSI";
                for (var i = 0; i < $scope.files.length; i++) {
                    var $file = $scope.files[i];
                            $upload.upload({
                                url: fileuploadurl,
                                file: $file,
                                progress: function (e) {
                                    // wait...
                                }
                            })
                              .then(function (data, status, headers, config) {
                                  alert('file is uploaded successfully');
                              });
                        }
                        alert('file is uploaded successfully');
            };

上面的代码给我错误$ upload未定义。我可以在上面的代码中知道我在哪里做错了吗？任何帮助，将不胜感激。谢谢。