Deselecting an upload file causes problems with fi

The following html is used to select some images for upload

<input type="file" id="files" ngf-select="select(files)" ng-model="files" name="file" accept="image/*" ngf-max-size="'2MB'" required ngf-multiple="true">

I am using the following html to display selected images as thumbnails with a button to cancel the selected file prior to uploading them.

<div ng-repeat="f in files track by $index">
      <div ng-show="f.type.indexOf('image') > -1">    
      <img ngf-src="f" class="thumb">

          <button class= "btn btn-warning btn-cancel" ng-disabled="!myForm.$valid" 
              ng-click="cancelPic($index)">Cancel</button> 

          <br><br>
          <p>{{f.name}}</p>
          <br>
          <span class="progress" ng-show="f.progress >= 0">
            <div style="width:{{f.progress}}%" 
                  ng-bind="f.progress + '%'"></div>
          </span>
          <hr>
      </div>    
      </div>

In the controller when the cancel button is clicked:

$scope.cancelPic = function(index) {

        $scope.files[index] = undefined;

        //$scope.files.length--;
      }

This works to remove the selected image and its cancel button (via ng-show). The problem is when then the file is uploaded, here is the upload function

$scope.uploadPic = function(files) {
      for(var i = 0; i < $scope.files.length; i++) {
        var $file = $scope.files[i];
        (function(index) {
          $scope.upload[index] = Upload.upload({
            url: '/',
            method: 'POST',
            file: $file,
          }).progress(function (evt) {
              //error here
              $scope.files[index].progress = Math.min(100, parseInt(100.0 * evt.loaded / evt.total));
          }).then(function (response) {
            $timeout(function () {
            $file.result = response.data;
          });
          }, function (response) {
            if (response.status > 0)
            $scope.errorMsg = response.status + ': ' + response.data;
          });
          })(i);

          }
        }
      }]);

There is the following error:

TypeError: Cannot set property 'progress' of undefined
    at userCtrl.js:58

This is the line with the error:

$scope.files[index].progress = Math.min(100, parseInt(100.0 * evt.loaded / evt.total));

The cancelPic function doesn't change the index value which if 3 files were selected and one was removed with cancelPic the value of index is still 3. I added a line to decrement the files.length as:

$scope.files.length--;

Which does reduce the index to 2 but I still get the error as before plus when one file is removed with cancelPic two are removed from the selected files? I am not a little puzzled by that one.

The logic of the cancelPic function is faulty I think.

To remove an index from an array you should use splice function. So this should fix it for you:

$scope.cancelPic = function(index) {
   $scope.files.splice(index,1);
   $scope.files = $scope.files.slice(0);    
}

The second line is to change $scope.files object value so that validations would be triggered by angular. Just using the first line will not trigger $scope.$watch('files').