We create a class called NetModule.java and annotate it with @module to signal to Dagger to search within the available methods for possible instance providers. The methods that will actually expose available return types should also be annotated with @provides decorator. The Singleton annotation also signals to the Dagger compiler that the inst…

Dagger2.java

@Module
public class NetModule {

    String mBaseUrl;
    
    // Constructor needs one parameter to instantiate.  
    public NetModule(String baseUrl) {
        this.mBaseUrl = baseUrl;
    }

    // Dagger will only look for methods annotated with @Provides
    @Provides
    @Singleton
    // Application reference must come from AppModule.class
    SharedPreferences providesSharedPreferences(Application application) {
        return PreferenceManager.getDefaultSharedPreferences(application);
    }

    @Provides
    @Singleton
    Cache provideOkHttpCache(Application application) { 
        int cacheSize = 10 * 1024 * 1024; // 10 MiB
        Cache cache = new Cache(application.getCacheDir(), cacheSize);
        return cache;
    }

   @Provides 
   @Singleton
   Gson provideGson() {  
       GsonBuilder gsonBuilder = new GsonBuilder();
       gsonBuilder.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES);
       return gsonBuilder.create();
   }

   @Provides
   @Singleton
   OkHttpClient provideOkHttpClient(Cache cache) {
      OkHttpClient client = new OkHttpClient();
      client.setCache(cache);
      return client;
   }

   @Provides
   @Singleton
   Retrofit provideRetrofit(Gson gson, OkHttpClient okHttpClient) {
      Retrofit retrofit = new Retrofit.Builder()
                .addConverterFactory(GsonConverterFactory.create(gson))
                .baseUrl(mBaseUrl)
                .client(okHttpClient)
                .build();
        return retrofit;
    }
}