MVP with Retrofit2 and RxJava2 - 5

I know I know… who would not know the world-famous library from Square that takes the networking mess we need and clears it up organizing it in a simple way for us to use… but still, let’s see how Retrofit2 has been set up for this project ;)

Basically there is a class called ServiceGenerator where we configure the RetrofitService and then we store an instance of it in the Application class to be retrieved when needed (it could also be done via Dagger2 but this is out of the scope of these articles)

public class ServiceGenerator {
    
   private static String baseUrl = "http://uinames.com/";
   private NetworkAPI networkAPI;

   public NetworkService() {
      this(baseUrl);
   }

   private NetworkService(String baseUrl) {
      OkHttpClient.Builder httpClient = new OkHttpClient.Builder()
         .addInterceptor(new HttpLoggingInterceptor()
            .setLevel(HttpLoggingInterceptor.Level.BODY));

      GsonConverterFactory gsonConFactory = GsonConverterFactory
         .create(new GsonBuilder()
              .registerTypeAdapterFactory(MyAdapterFactory.create())
              .create());

      final Retrofit retrofit = new Retrofit.Builder()
           .baseUrl(baseUrl)
           .addConverterFactory(gsonConFactory)
           .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
           .client(httpClient.build())
           .build();

      networkAPI = retrofit.create(NetworkAPI.class);
   }

   public NetworkAPI getAPI() {
      return networkAPI;
   }

   public interface NetworkAPI {
      @GET("api/")
      Single<List<Person>> getGenderedNames(
         @Query("gender") String gender);

      @GET("api/")
      Single<List<Person>> getLocalisedNames(
         @Query("region") String region);
   }
}

It has two constructor to be able to start it off with a custom base URL or the predefined one

When building the service, first it applies an HttpLoggingInterceptor to help us log and debug the network calls, then it adds a GSON conversion factory to easily parse the network results into the JSON specified by MyModel and finally it creates an implementation of the API endpoints

Also, the API endpoints return a Single, which fits very well to be used together with RxJava and the MVP pattern as we will see later on

 

Bonus info: MyAdapterFactory

When/if using AutoValues (library from Google for data classes) like we did in the class Person things look so nifty

@AutoValue
public abstract class Person implements Parcelable {

   public abstract String name();
   public abstract String surname();
   public abstract String gender();
   public abstract String region();
   public static TypeAdapter<Person> typeAdapter(Gson gson) {
      return new $AutoValue_Person.GsonTypeAdapter(gson);
   }
}

AutoValue is precious and dear because:

• Acts on abstract classes that will be generated at compile time

• Generates immutable classes

• Generated classes also contains hashCode(), toString() and equals()

• The library comes with nice extensions (for example for Parcelable, Gson, With, etc.)

For a nice understanding of the topic I recommend you read this great article, but here I wanted to tell you about something else…

In order for the network result to be parsed properly to a JSON first we need to define a TypeAdapter in the AutoValue class, then to avoid adding each generated TypeAdapter to our Gson instance manually, we can use a common MyAdapterFactory class to pass to Retrofit in the method addConverterFactory()

@GsonTypeAdapterFactory
abstract class MyAdapterFactory implements TypeAdapterFactory {

   // Method to access the package private generated implementation
   static TypeAdapterFactory create() {
      return new AutoValueGson_MyAdapterFactory();
   }
}

Next topic will be binding of the MVP