PUT reader.result上的角度ng-file-upload未定义

Question

我正在尝试更新模块而不上传新图像。问题是，如果我没有上传新图像，而是尝试使用我从api读回的图像，那么在调试时它会显示read.result is undefined。我认为读者期待一个图像流，我给它一个网址。不知道如何解决这个问题。

API采用DataURL作为图像，然后将其存储并将图片路径/网址放在ImageURLPATH中。

代码：

angular.module('Services.modulesPUT', [])
.service('modulesPUTSrvc', function (baseSrvc, $http,modulesGETSrvc,$rootScope,$state, myConfig) {
  var fObject = {};
  fObject.myForm = {};
  fObject.details = {};
  fObject.imgObject = {};

  fObject.put = function ()
  {
    var imageData;
    if (fObject.myForm.$valid)
    {
      var reader = new window.FileReader();

      reader.readAsDataURL(fObject.details.ImageURLPath);
      reader.onloadend = function () {
        $rootScope.loading = true;
        var result = $http({
          method: "PUT",
          dataType: 'json',
          data: {
            "DataURI": reader.result
          },
          url: myConfig.baseURL + 'odata/Modules(' + fObject.details.ModuleId + ')'
        });
        result.success(function (data) {
          $rootScope.loading = false;
          baseSrvc.toastMessage('Module has successfully been updated.');
          $state.go('base.modules.get');
        });
        
        result.error(function (data) {
          $rootScope.loading = false;
          baseSrvc.returnError(data);
        });
      };
    } 
    else
    {
      baseSrvc.toastMessage('Please input all required fields.');
    };
  };
  
  return fObject;
});

<div class="md-block" flex-gt-sm>
  <div class="imageUpload">
    <md-tooltip md-direction="left">
      Click here to select your image
    </md-tooltip>
    <div class="button"
         required
         ngf-select
         ng-model="srvcObject.details.DataURI"
         name="file"
         ngf-pattern="'image/*'"
         ngf-accept="'image/*'"
         ngf-max-size="20MB"
         ><span ng-show="!srvcObject.details.DataURI">Select <br/> Course Image</span></div>
    <div class="preview"
         ngf-src="srvcObject.details.ImageURLPath"
         ngf-background="srvcObject.details.ImageURLPath"></div>
  </div>
</div>