title: OnSuccessListener is not called for every item in an ArrayList
body: <p>I have an ArrayList of my Post class which contains all posts made by the user. The post class has a member variable which contains the path inside FireBase storage to the image for that post. I am trying to loop through the list, use that path to grab the download URL for each post, and add the images to a gridview with an adapter. However, not all URL's are grabbed. When testing it on my profile, the profile page only displays 4 posts, when I have actually made 7. Here is the code in question:</p>
  
  <pre><code>for (Post p : post_list)
                  {
                      //Log.d("notebook", "loop");
                      storage.child(p.getPath()).getDownloadUrl().addOnSuccessListener(new OnSuccessListener&lt;Uri&gt;() {
                          @Override
                          public void onSuccess(Uri uri) {
                              urls.add(uri.toString());
                              GridAdapter gridAdapter = new GridAdapter(getActivity(), urls);
                              gridView.setAdapter(gridAdapter);
                          }
                      });
                  }
  </code></pre>
  
  <p>The loop does loop 7 times as it should, but the listener is only called 4 times.</p>