LiveData Observer not Called

Question

I have an activity, TabBarActivity that hosts a fragment, EquipmentRecyclerViewFragment. The fragment receives the LiveData callback but the Activity does not (as proofed with breakpoints in debugging mode). What's weird is the Activity callback does trigger if I call the ViewModel's initData method. Below are the pertinent sections of the mentioned components:

TabBarActivity

override fun onCreate(savedInstanceState: Bundle?) {     super.onCreate(savedInstanceState)     initVM()     setContentView(R.layout.activity_nav)     val equipmentRecyclerViewFragment = EquipmentRecyclerViewFragment()     supportFragmentManager             .beginTransaction()             .replace(R.id.frameLayout, equipmentRecyclerViewFragment, equipmentRecyclerViewFragment.TAG)             .commit()     navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener)  }  var eVM : EquipmentViewModel? = null private fun initVM() {     eVM = ViewModelProviders.of(this).get(EquipmentViewModel::class.java)     eVM?.let { lifecycle.addObserver(it) } //Add ViewModel as an observer of this fragment's lifecycle     eVM?.equipment?.observe(this, loadingObserver)//        eVM?.initData() //TODO: Not calling this causes Activity to never receive the observed ∆ } val loadingObserver = Observer<List<Gun>> { equipment ->     ...} 

EquipmentRecyclerViewFragment

override fun onCreate(savedInstanceState: Bundle?) {     super.onCreate(savedInstanceState)     columnCount = 2     initVM() }  //MARK: ViewModel Methods var eVM : EquipmentViewModel? = null private fun initVM() {     eVM = ViewModelProviders.of(this).get(EquipmentViewModel::class.java)     eVM?.let { lifecycle.addObserver(it) } //Add ViewModel as an observer of this fragment's lifecycle     eVM?.equipment?.observe(this, equipmentObserver)     eVM?.initData() } override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {     val view = inflater.inflate(R.layout.fragment_equipment_list, container, false)     if (view is RecyclerView) { // Set the adapter         val context = view.getContext()         view.layoutManager = GridLayoutManager(context, columnCount)         view.adapter = adapter     }     return view } 

EquipmentViewModel

class EquipmentViewModel(application: Application) : AndroidViewModel(application), LifecycleObserver { var equipment = MutableLiveData<List<Gun>>() var isLoading = MutableLiveData<Boolean>()  fun initData() {     isLoading.setValue(true)     thread { Thread.sleep(5000) //Simulates async network call         var gunList = ArrayList<Gun>()         for (i in 0..100){             gunList.add(Gun("Gun "+i.toString()))         }         equipment.postValue(gunList)         isLoading.postValue(false)     } } 

The ultimate aim is to have the activity just observe the isLoading MutableLiveData boolean, but since that wasn't working I changed the activity to observe just the equipment LiveData to minimize the number of variables at play.

Answer 1

To get same reference of ViewModel of your Activity you need to pass the same Activity instance, you should use ViewModelProviders.of(getActivity). When you pass this as argument, you receive instance of ViewModel that associates with your Fragment.

There are two overloaded methods:

ViewModelProvider.of(Fragment fragment)  ViewModelProvider.of(FragmentActivity activity) 

For more info Share data between fragments

Answer 2

I put this code inside the onActivityCreated fragment, don't underestimate getActivity ;)

if (activity != null) {                  globalViewModel = ViewModelProvider(activity!!).get(GlobalViewModel::class.java)     }   globalViewModel.onStop.observe(viewLifecycleOwner, Observer { status ->             Log.d("Parent Viewmodel", status.toString())         }) 

This code helps me to listening Parent ViewModel changes in fragment.