how get all data from FirebaseFirestore before return statement

Issue

I need a function to get all data/notes from FirebaseFirestore. How do I make this function wait for all data before return?

I think this function I created is not working in the main thread and return before getting data from firebase

    public static ArrayList<NoteFB> getNotes() {

        FirebaseFirestore db = FirebaseFirestore.getInstance();
        final String TAG = "FB Adapter";

        final ArrayList<NoteFB> doFBs = new ArrayList<>();
        db.collection("notesItem")
                .get()
                .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()) {
                            for (QueryDocumentSnapshot document : task.getResult()) {
                                Log.d(TAG, document.getId() + " => " + document.getData());
                                doFBs.add(document.toObject(NoteFB.class));
                            }
                        } else {
                            Log.w(TAG, "Error getting documents.", task.getException());
                        }
                    }
                });

        return doFBs;
    }

        MyFBAdapter myFBAdapter = new MyFBAdapter(ShowActivity.this, FBAdapter.getNotes());

        rvContacts.setAdapter(myFBAdapter);

This code returns an empty ArrayList that creates an empty recyclerview.

Solution

Lots of these questions popping up lately. I had found the solution a while back : Using the Tasks API.

public static ArrayList<NoteFB> getNotes() {

    FirebaseFirestore db = FirebaseFirestore.getInstance();
    final String TAG = "FB Adapter";

    final ArrayList<NoteFB> doFBs = new ArrayList<>();

    try {
        Task<QuerySnapshot> taskResult = Tasks.await(db.collection("notesItem").get(), 2, TimeUnit.SECONDS)
        for (QueryDocumentSnapshot document : task.getResult()) {
            Log.d(TAG, document.getId() + " => " + document.getData());
            doFBs.add(document.toObject(NoteFB.class));
         }

    } catch(Exception e) {
         Log.w(TAG, "Error getting documents.", e.localizedString());
    }
    return doFBs
}

Forgive me if I made any syntax errors my Java is a little rusty.

Make sure you are calling this code OFF the main thread, otherwise it will crash.

Answered By - Sean Blahovici