MainActivity.java

package com.example.dodo.popularmoviesfinal.Activities;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;

import com.example.dodo.popularmoviesfinal.Adapters.MoviesAdapter;
import com.example.dodo.popularmoviesfinal.Models.MovieResponse;
import com.example.dodo.popularmoviesfinal.Models.MoviesData;
import com.example.dodo.popularmoviesfinal.Network.ApiInterface;
import com.example.dodo.popularmoviesfinal.R;

import java.util.ArrayList;
import java.util.List;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

/**
 * The correct would be create a object that contains a list of movies.
 * Then, you can create the API interface returns that responde object.
 */
public class MainActivity extends AppCompatActivity implements MoviesAdapter.MoviesAdapterOnClickHandler {

    private static final String TAG = MainActivity.class.getSimpleName();

    private final static String API_KEY = "90cfeb2390166bcd501adabe6f68e59a";
    private static final String BASE_URL = "http://api.themoviedb.org/3/";

    private static Retrofit retrofit = null;
    private MoviesAdapter moviesAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        setupAdapter();
        fetchMostPopular();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.setting_menu, menu);
        //set menu item title based on sort key
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.most_popular) {
            fetchMostPopular();
            return true;
        }

        if (id == R.id.top_rated) {
            fetchTopRated();
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onClick(MoviesData moviesData) {
        Intent intent = new Intent(this, Details_Activity.class);
        intent.putExtra("movieModel", moviesData);
        startActivity(intent);
    }

    private void setupAdapter() {
        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
        moviesAdapter = new MoviesAdapter(new ArrayList<MoviesData>(), this, this);
        recyclerView.setAdapter(moviesAdapter);
        recyclerView.setLayoutManager(new GridLayoutManager(MainActivity.this, 2));
        recyclerView.setHasFixedSize(true);
    }

    private void fetchMostPopular() {

        if (retrofit == null) {
            retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }

        ApiInterface movieApiService = retrofit.create(ApiInterface.class);
        Call<MovieResponse> call = movieApiService.getPopular(API_KEY);
        call.enqueue(new Callback<MovieResponse>() {
            @Override
            public void onResponse(Call<MovieResponse> call, Response<MovieResponse> response) {
                List<MoviesData> mMovieList = response.body().getResults();
                moviesAdapter.setItems(mMovieList);
            }

            @Override
            public void onFailure(Call<MovieResponse> call, Throwable t) {
                // Log error here since request failed
                Log.e(TAG, t.toString());
            }
        });
    }

    private void fetchTopRated() {

        if (retrofit == null) {
            retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }

        ApiInterface movieApiService = retrofit.create(ApiInterface.class);
        Call<MovieResponse> call = movieApiService.getTop_rated(API_KEY);
        call.enqueue(new Callback<MovieResponse>() {
            @Override
            public void onResponse(Call<MovieResponse> call, Response<MovieResponse> response) {
                List<MoviesData> mMovieList = response.body().getResults();
                moviesAdapter.setItems(mMovieList);
            }

            @Override
            public void onFailure(Call<MovieResponse> call, Throwable t) {
                // Log error here since request failed
                Log.e(TAG, t.toString());
            }
        });
    }
}