ViewModel doesn't update ui after Activity and Fragment was created second time

Question

I have an app which is opened/started from outside via PWA. Then data is fetched from a service and passed to the UI via a Shared ViewModel. When I start the app for the first time it's working fine. When I start it again, ui will not be updated anymore, even if I receive tracking informations. My guess is that it is because the app is destroyed and re-created. However, the .observe is also reassigned so it should workout.

In Fragment

    private val locationUpdateViewModel: LocationUpdateViewModel by activityViewModels()

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        locationUpdateViewModel.uiElapsedTime.observe(viewLifecycleOwner) { elapsedTime ->
                updateElapsedTime(elapsedTime)
        }

        startTracking()
    }

In ViewModel

val uiElapsedTime: MutableLiveData<String> = MutableLiveData()

fun locationReceived(){
    ...
    uiElapsedTime.postValue("$time")
}

Unfortunately moving startTracking() or Observing to onStart() or onResume() didn't help. I added different logs of every lifecycle process. Attached you can see two things i did.

1. When switching to another app and back = WORKING

   2022-03-18 10:30:27.168 16851-16851/de.locations D/TAG: Activity onRestart
   2022-03-18 10:30:27.197 16851-16851/de.locations D/TAG: TrackDetailLiveFragment onCreate
   2022-03-18 10:30:27.430 16851-16851/de.locations D/TAG: Service is running: true 
   2022-03-18 10:30:28.002 16851-16851/de.locations D/TAG: TrackDetailLiveFragment onResume
   2022-03-18 10:30:28.002 16851-16851/de.locations D/TAG: locationUpdateViewModel.loadActiveTrackData()
   2022-03-18 10:30:47.540 17461-17461/de.locations D/TAG: BroadcastReceiver onReceive
   2022-03-18 10:30:47.543 17461-17461/de.locations D/TAG VIEMODEL: speed 132.79279558118925 distance 404.7006743398197 totalDistance 0.81766925647099 elapsedTime 18 syncWithAPI false

2. When opening app again via pwa = NOT WORKING

   2022-03-18 10:36:37.517 17461-17461/de.locations D/TAG: Activity destroyed
   2022-03-18 10:36:37.609 17461-17461/de.locations D/TAG: TrackDetailLiveFragment onDestroy
   2022-03-18 10:36:38.150 17461-17461/de.locations D/TAG: Activity onCreate
   2022-03-18 10:36:38.211 17461-17461/de.locations D/TAG: TrackDetailLiveFragment onCreate
   2022-03-18 10:36:38.312 17461-17461/de.locations D/TAG: Service is running: true 
   2022-03-18 10:36:38.594 17461-17461/de.locations D/TAG: TrackDetailLiveFragment onStart
   2022-03-18 10:36:38.608 17461-17461/de.locations D/TAG: TrackDetailLiveFragment onResume
   2022-03-18 10:36:38.608 17461-17461/de.locations D/TAG: locationUpdateViewModel.loadActiveTrackData()
   2022-03-18 10:36:47.540 17461-17461/de.locations D/TAG: BroadcastReceiver onReceive
   2022-03-18 10:36:47.543 17461-17461/de.locations D/TAG VIEMODEL: speed 133.79279505888925 distance 401.7009233398197 totalDistance 0.81762263647099 elapsedTime 22 syncWithAPI false

Answer 1

I think when the app starts again, the Activity or Fragment is not recreated. Because when it first time starts, it works.

According to your code, I think your fragment must not recreate, if your fragment is resued, we should in the OnActivityCreate to restore the data, Because the fragment is not created when it is resued, so the onViewCreate the method will not be called in that situation.

At the same time, the observer should only add the onCreate method to avoid adding it many times.

so move the startTracking() method to onResume or onActivityCreate

Answer 2

After days i found the problem and solution. (Re)-creating the fragment and updating viewmodel worked as it should. The problem was, that i used the "old" BroadcastReveiver. I use a Service to receive location updates any my BroadcastReceiver listens for changes. I had to unregister and register again.