Java (android) code for selecting multiple images gallery, upload to GoogleVision, and save results properly.

I need to select multiple images from user's gallery, upload to Google Vision, and save results correctly (without crashing, and photo correctly assigned to result) For single image, I can get its result without problem using Google Vision's sample code, but I can't do the same for multiple selections (batch processing). I can't figure out whether it's because I overload UI thread by not using AsyncTask (very likely) or something else. My code is plagued with problems so I believe it would be better to start from scratch but if you want my code or Google's sample code then please feel free to ask.