Injecting dependencies into background service in Dagger2

Question

I have Shared Preferences as a dagger singleton component. I need to inject it into background services like FirebaseInstanceService. Here's my attempt:

public class InstanceIDListenerService extends FirebaseInstanceIdService {
    @Inject
    Preferences preferences;

    @Override
    public void onTokenRefresh() {
        ((MyApp) getApplication()).getSingletonComponent().inject(this);
        String refreshedToken = FirebaseInstanceId.getInstance().getToken();
        preferences.setFcmToken(refreshedToken);

    }
}

It is used in this way:

   <service android:name="com.fcm.InstanceIDListenerService">
            <intent-filter>
                <action android:name="com.google.firebase.INSTANCE_ID_EVENT" />
            </intent-filter>
   </service>

Should I use ((MyApp) getApplication()).getSingletonComponent().inject(this); in the onTokenRefresh listener? Is this the correct listener to inject dependencies?

Answer 1

I know this question is old, but I've just been hitting my head on this over the last few hours, and found the solution.

With the new Dagger2 version, you can now have your application implement the HasServiceInjector interface, which lets you inject stuff into services.

A simple example:

1) Create your services module:

@Module
abstract class ServicesModule {

  @ContributesAndroidInjector
  abstract SomeService ProvideSomeService();
}

2) Add it to your App component:

@Component(modules = {
  AndroidSupportInjectionModule.class,
  AppModule.class,
  ActivitiesModule.class,
  ServicesModule.class
})
public interface AppComponent {

  @Component.Builder
  interface Builder {
    @BindsInstance
    Builder application(App application);

    AppComponent build();
  }

  void inject(App app);
}

3) Have your application implement the said interface:

public class App extends Application implements HasActivityInjector, HasServiceInjector {

  @Inject
  DispatchingAndroidInjector<Activity> activityInjector;
  @Inject
  DispatchingAndroidInjector<Service> serviceInjector;

  @Override
  public void onCreate() {
    super.onCreate();
    AppInjector.init(this);
  }

  @Override
  public AndroidInjector<Activity> activityInjector() {
    return activityInjector;
  }

  @Override
  public AndroidInjector<Service> serviceInjector() {
    return serviceInjector;
  }
}

4) Finally, inject your service:

public class SomeService extends Service {

  @Inject
  SomeDependency dependency;

  @Override
  public void onCreate() {
    AndroidInjection.inject(this);
    super.onCreate();
  }

  // Do things with your dependencies

}

I'm using a Service in the example, but my actual use case was with FirebaseInstanceIdService as well. And this worked.