Android: Firebase taking too much time to fetch data

Question

I am using Realtime database feature of Firebase in my Application. Database looks like this:

The nodes 104, 1040... are having further elements/data. I'm fetching this data ordering it by value at a node 'updatedAt' available within every Integer parent as shown in the snap. I am using onChildAddedListener() to fetch the last 20 elements. There are around 1050 nodes within 'results'.

The problem:

1. The fetching of data takes too much time, around 30 sec, even on high speed WiFi.

2. Does Firebase allows any callback to notify that data has been fetched? I want to append every custom object to the ArrayList received from Firebase and pass it through intent to another activity. I am counting the objects received and when it becomes 20, I open up my Activity. Is that the only way to do so? If there is some better way out, do suggest.

Here is my code:

 public class Splash extends AppCompatActivity{

        private static final String TAG = "Splash Activity";
        private ArrayList<News> NewsArrayList = new ArrayList<>();   
        private DatabaseReference newsReference;
        private int position = 0;

        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_splash);

            newsReference = FirebaseDatabase.getInstance().getReference().child("results");
            Query queryNewsReference = newsReference.orderByChild("updatedAt").limitToLast(20);
            fetchNews(queryNewsReference);
        }

        private void fetchNews(Query queryNewsReference) {

            queryNewsReference.addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                    Log.d(TAG, "onChildAdded:" + dataSnapshot.getKey());
                    News newsObject = dataSnapshot.getValue(News.class);
                    Log.d(TAG,"News Title: "+ newsObject.getVideo_title());
                    NewsArrayList.add(newsObject);
                    position++;
                    if(position == 20){
                    startMainActivity(); 
                    }
                }
                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String s){
                    Log.d(TAG, "onChildChanged() called on key: "+ dataSnapshot.getKey());
                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {
                    Log.d(TAG, "onChildRemoved() called on key: "+ dataSnapshot.getKey());
                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String s) {
                    Log.d(TAG, "onChildMoved() called on key: "+ dataSnapshot.getKey());
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                    Log.e(TAG,"Database Error: "+databaseError.toString());
                }
            });
        }

        private void startMainActivity() {
            Intent intent = new Intent(Splash.this,MainActivity.class);
            intent.putExtra("NewsList",NewsArrayList);
            Splash.this.startActivity(intent);
        }

Answer 1

Try reconnecting to firebase before adding value listener:

private void fetchNews(Query queryNewsReference) 
{    
    if (FirebaseDatabase.getInstance() != null)
    {
        FirebaseDatabase.getInstance().goOffline();
    }

    FirebaseDatabase.getInstance().goOnline();

    queryNewsReference.addChildEventListener(new ChildEventListener() {

    ...
}