MainActivity.java

public class MainActivity extends AppCompatActivity {

    RecyclerView recyclerView;
    SwipeRefreshLayout swipeRefreshLayout;
    FilmAdapter filmAdapter;
    StarWarsApi starWarsApi;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        recyclerView = (RecyclerView) findViewById(R.id.rvFilms);
        swipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.srl);

        setTitle("All Star Wars Films");

        filmAdapter = new FilmAdapter(null, new FilmAdapter.OnFilmClickListener() {
            @Override
            public void onFilmClick(Film film) {
                FilmActivity.start(MainActivity.this, film.episodeId);
            }
        });
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(filmAdapter);

        swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                loadFilms();
            }
        });

        Gson gson = new GsonBuilder()
                .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
                .create();
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("http://swapi.co/api/")
                .addConverterFactory(GsonConverterFactory.create(gson))
                .build();
        starWarsApi = retrofit.create(StarWarsApi.class);

        loadFilms();
    }

    private void loadFilms() {
        swipeRefreshLayout.setRefreshing(true);
        starWarsApi.getAllFilms().enqueue(new Callback<FilmResponse>() {
            @Override
            public void onResponse(Call<FilmResponse> call, Response<FilmResponse> response) {
                filmAdapter.setFilms(response.body().results);
                swipeRefreshLayout.setRefreshing(false);
            }

            @Override
            public void onFailure(Call<FilmResponse> call, Throwable t) {
                Toast.makeText(MainActivity.this, t.getMessage(), Toast.LENGTH_SHORT).show();
                swipeRefreshLayout.setRefreshing(false);
            }
        });
    }
}