Firebase on android not retrieving data

I have been able to successfully upload and delete data from my firebase repo using the guide here: https://www.firebase.com/docs/android/guide/saving-data.html

However if I try and retrieve the data using the the Firebase guide here: https://www.firebase.com/docs/android/guide/retrieving-data.html

the app activity just hangs - there is no call back to onDataChange or onCancel. I am using the exact code in the example which has worked until this point in the guide (in my Activity onCreate() method):

Firebase ref = new Firebase("https://docs-examples.firebaseio.com/web/saving-data/fireblog/posts"); ref.addValueEventListener(new ValueEventListener() { @Override public void onDataChange(DataSnapshot snapshot) { System.out.println(snapshot.getValue()); } @Override public void onCancelled(FirebaseError firebaseError) { System.out.println("The read failed: " + firebaseError.getMessage()); } }); 

There is data at the example URL so should work. I am running on a phone running Android 4.0.3.

What am I doing wrong?

Thanks, Riz

Edit: I tried on my Samsung Note 4 running Android 5.1.1 and Firebase works fine. Doesn't work on my Huawei running Android 4.0.3. Something to do with the Android version?

Edit 2: So it turns out the answer below was right after all. I found an old bit of code in one of my helper classes that was pausing the thread whilst it waited for something. I rewrote it to be truly asynchronous and it fixed the problem. Many thanks - I have accepted the answer.