High memory usage looping through PHAssets and calling requestImageForAsset

Question

I\'m using an image picker library to allow the user to select many images from their photo library. They are returned as an array of PHAssets. Then, I want to

Answer 1

I solved it with a recursive method that ensures that the completion block is finished before next iteration. This way it is possible to get thousands of photos with very low memory. Here is what it does:

Given an array of indices of selected photos in the camera roll

1. Request first object in array.
2. In completion block, remove first object in array and call same method again.
3. Repeat until array is empty

Here is the code.

- (void)processPhotos
{
  NSIndexPath *indexPath = [_selectedPhotosArray objectAtIndex:0];
  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    PHAsset *asset = [_allPhotos objectAtIndex:indexPath.row];
    [self.imageManager requestImageForAsset:asset
                                 targetSize:PHImageManagerMaximumSize
                                contentMode:PHImageContentModeAspectFill
                                    options:self.imageRequestOptions
                              resultHandler:^(UIImage * _Nullable result, NSDictionary * _Nullable info) {
      NSError *error = [info objectForKey:PHImageErrorKey];
      if (_selectedPhotosArray.count > 0) {
        [_selectedPhotosArray removeObjectAtIndex:0];
      }
      if (error) { 
        NSLog(@"[CameraRoll] Image request error: %@",error);
      } else {
        if (result != nil) {
          [self processImage:result];
        }
      }
      if (_selectedPhotosArray.count > 0) {
        // Recurring loop
        [self processPhotos];
      }
    }];
  });
}

Make sure to check if array not empty before calling this method for the first time.