loadArticles.java

    private void loadArticles() {
        repository.addListener(new FirebaseDatabaseRepository.FirebaseDatabaseRepositoryCallback<Article>() {
            @Override
            public void onSuccess(List<Article> result) {
                articles.setValue(result);
            }

            @Override
            public void onError(Exception e) {
                articles.setValue(null);
            }
        });
    }