Cannot get latitude and longitude from Google Maps using Retrofit

Question

I have defined a Model class along with an interface inside it. The code is as follows:

public class MapModel {
    MapContract.Presenter mPresenter;
    private Location mResLocation;
    private static final String TAG = MapModel.class.getSimpleName();

    public MapModel(MapContract.Presenter presenter) {
        mPresenter = presenter;
    }
    public static WebServiceInterface WebServiceInterface = RetrofitServiceGenerator.create(WebServiceInterface.class);


    public void queryAddress(String address) throws IOException {

        WebServiceInterface .lookupAddress(Constants.GOOGLE_API_KEY, address).enqueue(
                new Callback<Result>() {
                    @Override
                    public void onResponse(Call<Result> call, Response<Result> response) {


                        mResLocation = response.body().getGeometry().getLocation();


 Log.i(TAG, "onResponse: " + response.toString());
                            Log.i(TAG, "Location : " + mResLocation.getLat() + " : " + mResLocation.getLat());
                            mPresenter.onSearchSuccess(mResLocation);
                        }



                  @Override
                    public void onFailure(Call<Result> call, Throwable t) {mPresenter.onSearchFailed("Search failed");
                    }
                }
        );
    }
    public interface WebServiceInterface {

        @GET("json")
        Call<Result> lookupAddress(@Query("key") String apiKey, @Query("address") String searchTerm);
    }

}

My retrofit generator is as follows:

public class RetrofitServiceGenerator {
    public static <S> S create(Class<S> serviceClass) {
        HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
        interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
        OkHttpClient client = new OkHttpClient.Builder().addInterceptor(interceptor)
                .readTimeout(30, TimeUnit.SECONDS)
                .connectTimeout(30, TimeUnit.SECONDS).build();
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("https://maps.googleapis.com/maps/api/geocode/")
                .client(client)
                .addConverterFactory(GsonConverterFactory.create())
//                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .build();

        return retrofit.create(serviceClass);
    }
}

The problem that I have is that when I call the method queryAddress, it seems to return null. I have created POJO objects for the json result that I get using http://www.jsonschema2pojo.org/. You can see the complete code as well as POJO classes class here. The error that I get is as follows:
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Double sematec.mehdi.mymap.webmodels.Location.getLat()' on a null object reference I think my request is correct because okhttp log shows a correct json response for it. So the culprit is somewhere else. Does anyone know where I am wrong?

Answer 1

I finally found the source of problem. If you look at the web models, there is also a class GoogleMapModel. The calling method must return that type. Next, we'll extract location info from it. So, the code becomes:

public class MapModel {
    MapContract.Presenter mPresenter;
    private Location mResLocation;
    private static final String TAG = MapModel.class.getSimpleName();

    public MapModel(MapContract.Presenter presenter) {
        mPresenter = presenter;
    }
    public static WebServiceInterface WebServiceInterface = RetrofitServiceGenerator.create(WebServiceInterface.class);


    public void queryAddress(String address) throws IOException {

        WebServiceInterface .lookupAddress(Constants.GOOGLE_API_KEY, address).enqueue(
                new Callback<GoogleMapModel>() {
                    @Override
                    public void onResponse(Call<GoogleMapModel> call, Response<GoogleMapModel> response) {
                        mResLocation = response.body().getResults().get(0).getGeometry().getLocation();
                        mPresenter.onSearchSuccess(mResLocation);
                    }

                    @Override
                    public void onFailure(Call<GoogleMapModel> call, Throwable t) {mPresenter.onSearchFailed("Search failed");
                    }
                }
        );
    }
    public interface WebServiceInterface {

        @GET("json")
        Call<GoogleMapModel> lookupAddress(@Query("key") String apiKey, @Query("address") String searchTerm);
    }

}

Answer 2

The problem is that you log the lat/long before set the object from response. This line

Log.i(TAG, "Location : " + mResLocation.getLat() + " : " + mResLocation.getLat());

should go after you set the object from the response.

So it should be:

mResLocation = response.body().getGeometry().getLocation();
Log.i(TAG, "Location : " + mResLocation.getLat() + " : " + mResLocation.getLat());