Dagger 2 Third part Injection Android

Question

Hi im trying to figure out how to do a clean third party injection. I want to inject Otto bus properly into my services and activities. Iv seen that you can use inject on constructor, but since I dont have any constructor with Android, i wonder how I can then inject my bus.

Iv created a module which provides a new instance of the bus. Iv also created a component which has an interface for the Bus object.

But how can I get this injected and where should I initiate my graph?

Since the objectGraph from Dagger 1 is removed, i use the Dagger_.... component and create() in the application class, but how should I inject it into whatever activity or service?

Should I create the component in every onCreate and get the bus from there? Or is it possible to @Inject like Dagger 1? Please tell me because right now it seems much more clumpy and complicated than Dagger 1 way of doing it.

@Component(modules = EventBusModule.class)
@Singleton
public interface EventBus {
    Bus bus();
}

@Module
public class EventBusModule {

   @Provides
   @Singleton
   public Bus provideBus() {
       return new Bus(ThreadEnforcer.ANY);
   }
}

All i want to be able to do is:

public class WearService extends WearableListenerService {
    private static final String TAG = WearService.class.getSimpleName();

    @Inject
    protected Bus bus;

   @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        bus.register(this);
        return START_STICKY;
    }
}

I look at this example(https://github.com/LiveTyping/u2020-mvp) and see that its possible, but not sure how things is hanging together.

Can you show some code of your modules, components and the class in which you want to retrieve an instance of the Bus? — nhaarman
This is how I want to be able to do it, it was very similar to what i did in Dagger 1, but I used the ObjectGrap create and inject to create the object graph. Now since I want to use Dagger 2, im not sure where to instansiate the Graph and how I can inject the bus in a nice way — vonGohren

nhaarman nhaarman · Accepted Answer · 2015-03-05T08:27:13

It is quite usual to instantiate the Dagger component in the Application instance. Since you probably don't have a reference to your WearService from your Application class, you'll need to make the WearService ask your Application to provide the Bus.

You can do this in two ways:

By adding an inject(WearService wearService) method to your EventBus component:

@Component(modules = EventBusModule.class)
@Singleton
public interface EventBus {
    Bus bus();

    void inject(WearService wearService);
}

You can now keep a reference to your Component in your Application:

public class MyApplication extends Application {

    private EventBus mEventBusComponent;

    @Override
    public void onCreate() {
        super.onCreate();

        mEventBusComponent = Dagger_EventBus.create();
    }

    public void inject(WearService wearService) {
        mEventBusComponent.inject(wearService);
    }
}

From your WearService, ask your Application to inject it:

public class WearService extends WearableListenerService {
    private static final String TAG = WearService.class.getSimpleName();

    @Inject
    protected Bus bus;

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        ((MyApplication) getApplicationContext()).inject(this);
        bus.register(this);
        return START_STICKY;
    }
}

By retrieving the Bus manually. Add a getter method for the EventBus component in the Application:

public class MyApplication extends Application {

    private EventBus mEventBusComponent;

    @Override
    public void onCreate() {
        super.onCreate();

        mEventBusComponent = Dagger_EventBus.create();
    }

    public EventBus getEventBusComponent() {
        return mEventBusComponent;
    }
}

Then, in your WearService, call the bus() method:

public class WearService extends WearableListenerService {
    private static final String TAG = WearService.class.getSimpleName();

    private Bus bus;

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        bus = ((MyApplication) getApplicationContext()).getEventBusModule().bus();
        bus.register(this);
        return START_STICKY;
    }
}

For injecting the Bus into classes you can instantiate, you can use constructor injection:

public class MyClass() {

  private final Bus mBus;

  @Inject
  public MyClass(final Bus bus) {
    mBus = bus;
  }
}

Since Dagger knows how to create a Bus instance (because of your @Provides method), Dagger will now also know how to create a MyClass instance, no @Provides method necessary. For example, this will work:

    public class WearService extends WearableListenerService {
        private static final String TAG = WearService.class.getSimpleName();

        @Inject
        protected Bus bus;

        @Inject
        protected MyClass myClass;

        @Override
        public int onStartCommand(Intent intent, int flags, int startId) {
            ((MyApplication) getApplicationContext()).inject(this);
            bus.register(this);
            return START_STICKY;
        }
    }

The MyClass instance will automatically be created for you, with the same instance of Bus (since it is marked as @Singleton).

Dagger 2 Third part Injection Android

2 Answers