How to provide database to MyFirebaseMessagingService using Dagger 2 so that I can store fcm message locally in android

Question

How can I make it possible to pass database Instance to the MyFirebaseMessagingService class which extends FirebaseMessagingService so that I can save data payload locally?

Note: I already setup dagger 2 in my app, it's working perfectly.

Below is MyFirebaseMessagingService class:

class MyFirebaseMessagingService @Inject constructor(exampleOneDao: ExampleOneDao?) : FirebaseMessagingService() {

    override fun onMessageReceived(remoteMessage: RemoteMessage?) {
    //need db instance to store data payload locally (Room)
    }
}

And below is the AppModule class of Dagger 2

@Module(includes = arrayOf(ViewModelModule::class))
class AppModule() {

    // --- DATABASE INJECTION ---
    @Provides
    @Singleton
    internal fun provideDatabase(application: Application): MyDatabase {
        return Room.databaseBuilder(application,
               MyDatabase::class.java, "MyDatabase.db")
              .build()
    }

    @Provides
    @Singleton
    internal fun provideExampleOneDao(database: MyDatabase): ExampleOneDao {
        return database.exampleOneDao()
    }

    @Provides
    @Singleton
    internal fun provideMyFirebaseMessagingService(exampleOneDao: 
        ExampleOneDao): MyFirebaseMessagingService {
           return MyFirebaseMessagingService(exampleOneDao)
    }
}

Is it possible to provide database and dao to MyFirebaseMessagingService class?

I tried above method to provide exampleOneDao to the MyFirebaseMessagingService class, but it throws the following Exception

MyFirebaseMessagingService: java.lang.InstantiationException: java.lang.Class<com.example.user.app.firebase.messaging.MyFirebaseMessagingService> has no zero argument constructor

Thank You.

Answer 1

Finally got the solution from this link: https://github.com/googlesamples/android-architecture-components/issues/253

As MyFirebaseMessagingService is a Service class, so for injection in Service class, Dagger provides a way through which we can inject dependencies into Service class. Below are the steps to enable injection in service class:

1) Make Application implements HasServiceInjector and inject a DispatchingAndroidInjector for services.

public class App extends Application implements HasActivityInjector, HasServiceInjector {

    @Inject
    DispatchingAndroidInjector<Activity> dispatchingActivityInjector;

    // Add this line
    @Inject
    DispatchingAndroidInjector<Service> dispatchingServiceInjector;

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

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

    // override this method after implementing HasServiceInjector
    @Override
    public AndroidInjector<Service> serviceInjector() {
        return dispatchingServiceInjector;
    }

}

2) Create a new module to perform injection over your services.

@Module
abstract class ServiceBuilderModule {

    // for my case, the service class which needs injection is MyFirebaseMessagingService
    @ContributesAndroidInjector
    abstract MyFirebaseMessagingService contributeMyFirebaseMessagingService();

}

3) Register your new module in your application's component.

@Component(modules = {
        AndroidSupportInjectionModule.class,
        AppModule.class,
        ActivityBuilderModule.class,
        // Need to define previously created module class here
        ServiceBuilderModule.class
})
@Singleton
public interface AppComponent {
    @Component.Builder
    interface Builder {
        @BindsInstance
        Builder application(App application);
        AppComponent build();
    }
    void inject(App app);
}

4) And finally, override method onCreate of the service adding AndroidInjection.inject(this).

public class MyFirebaseMessagingService extends FirebaseMessagingService {

    //So now we are able to inject here same as we do in Activity. No need for constructor injection
    @Inject ExampleOneDao exampleOneDao

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

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        // use your dao here to store remoteMessage data payload into your database, e.g exampleOneDao.save(somethingHere)
    }


}