FirebaseService.java

FirebaseService.java

public class FirebaseService {
    //    ...
    public Single<List<Genre>> getGenres() {
        return Single.create(e ->
                firebaseDatabase.getReference().child("genres")
                        .addListenerForSingleValueEvent(new ValueEventListener() {
                            @Override
                            public void onDataChange(DataSnapshot dataSnapshot) {
                                List<Genre> genreList = new ArrayList<>();
                                for (DataSnapshot child : dataSnapshot.getChildren()) {
                                    genreList.add(child.getValue(Genre.class));
                                }
                                e.onSuccess(genreList);
                            }

                            @Override
                            public void onCancelled(DatabaseError databaseError) {
                                e.onError(new Throwable());
                            }
                        }));
    }
}