public class MainFragment extends Fragment
{
   protected RecyclerView recyclerView;
   protected NewsAdapter adapter;
   protected String API_KEY;
   String sourceTitle, sourceID;
   List<Articles> articleList;

public MainFragment() {

}

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState)
{
    ViewGroup root = (ViewGroup) inflater.inflate(R.layout.fragment_main, null);

    sourceTitle = "ABC News";
    sourceID = "abc-news";

    getActivity().setTitle(sourceTitle);

    API_KEY = getString(R.string.API_KEY);

    recyclerView = root.findViewById(R.id.recyclerview);

    RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getActivity().getApplicationContext());
    recyclerView.setLayoutManager(mLayoutManager);
    recyclerView.setItemAnimator(new DefaultItemAnimator());

    ApiInterface apiService = ApiClient.getClient().create(ApiInterface.class);

    Call<News> call = apiService.getArticles(sourceID, API_KEY);

    call.enqueue(new Callback<News>()
    {
        @Override
        public void onResponse(Call<News> call, Response<News> response)
        {

           //This is where the error occurs
            articleList = response.body().getArticles();
        }

        @Override
        public void onFailure(Call<News> call, Throwable t)
        {
            Toast.makeText(getActivity(), "Error in API Call", Toast.LENGTH_SHORT).show();
        }
    });

    if(articleList.isEmpty() || articleList.size() == 0)
    {
        recyclerView.setAdapter(null);
        Toast.makeText(getActivity(), "Error in List", Toast.LENGTH_SHORT).show();
    }
    else
    {
        adapter = new NewsAdapter(articleList, getActivity());
        recyclerView.setAdapter(adapter);
    }


    recyclerView.addOnItemTouchListener(new RecyclerTouchListener(getActivity().getApplicationContext(), recyclerView, new ClickListener() {
        @Override
        public void onClick(View view, int position)
        {
            //onclick code
        }

        @Override
        public void onLongClick(View view, int position) {
        }
    }));
    return root;
}

public interface ApiInterface
 {
   @GET("top-headlines")
   Call<List<News>> getArticles(@Query("sources") String source, @Query("apiKey") String apiKey);
 }

public class ApiClient
 {
  public static final String BASE_URL = "https://newsapi.org/v2/";
  private static Retrofit retrofit = null;


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