Dagger 2 Third part Injection Android

问题:

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.

回答1:

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).

回答2:

After some discususins with Niek regarding my question, I went to the source to find my answer. I asked on the github repo of dagger 2, and the answer can be found here:

https://github.com/google/dagger/issues/128#issuecomment-86702574

Its very deliberate and posts different solutions to my issue.