@Override
    public void onCreate() {
        retrofitInterface = RetrofitClient.getInstance().create(RetrofitInterface.class);
        loadAllData();
    }

    private void loadAllData(){
        compositeDisposable.add(retrofitInterface

                .getAllCountries()
                .flattenAsObservable((Function<List<Country>, Iterable<?>>) countries -> countries)
                .flatMap( country -> getFlags(country.getFlag))
                .subscribe());

    }