Android - Firebase: Waiting for SingleValueEventListener

Question

I am using a SingleValueEventListener to receive data once from my firebase. These data should be written to a list, in order to display it on the screen.

ref.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot friendChild : dataSnapshot.getChildren()) {
                String username = friendChild.getKey().toString();
                mAppList.add(username);
                System.out.println(username);
            }
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    });

Is there any possibility to wait for the SingleEventListener until continuing the further application?

Thanks