Observe LiveData from foreground service

问题

I have a repository which holds the LiveData object and is used by both activity and a foreground service through a ViewModel. When I start observing from the activity everything works as expected. However observing from the service doesn't trigger the Observe. This is the code I use

class MyService: LifecycleService() {
     lateinit var viewModel: PlayerServiceViewModel

     override fun onCreate() {
          viewModel = MyViewModel(applicationContext as Application)
     }

     override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
          viewModel.getLiveData().observe(this, Observer { data ->
            // Do something with the data
        })
     }
}

Any ideas why it doesn't work and I don't receive the data?

回答1:

I used ViewModel with LiveData in LifecycleActivity and Fragments it works and observes data as expected.

Coming to your problem, when you create new ViewModel from Service or any another Activity it creates new instance of all the LiveData and other dependencies required for ViewModel to query from Repository and ultimately DAO. If you are not using the same DAO for both ViewModels your LiveData may not update as it is observing on different instance of DAO.

I used Dagger2 in my project to maintain Singleton instances for DAO and other common dependencies. So you can try making your Repository and DAO singleton to keep it consistent across the Application.

I tried it using with Services with LifecycleService with same flow and it worked for me.

I got following output when data changed form null to pulled data

D/ForegroundService: onStartCommand: Resource{status=LOADING, message='null', data=null}
D/ForegroundService: onStartCommand: Resource{status=SUCCESS, message='null', data=TVShow(id=14,...

At first it showed null data as data wasn't present in database After pulling data from network and updating into database Observer observed data automatically.

Worked out using following code

public class ForegroundService extends LifecycleService {

    private static final String TAG = "ForegroundService";

    private TVShowViewModel tvShowViewModel;
    private TVShow tvShow;

    @Inject TVShowDataRepo tvShowDataRepo;

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

        AndroidInjection.inject(this);
        tvShowViewModel = new TVShowViewModel(tvShowDataRepo);
        tvShowViewModel.init(14);
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        tvShowViewModel.getTVShow().observe(this, tvShowResource -> {
            Log.d(TAG, "onStartCommand: " + tvShowResource);
        });
        return super.onStartCommand(intent, flags, startId);
    }
}

来源：https://stackoverflow.com/questions/44708202/observe-livedata-from-foreground-service

标签

android

android-service

android-livedata