ViewModel set data in Activity and use in Fragment

Question

I am trying no implement ViewModel, plaese help me get my head around this. I wish to set data in the Activity and use it in Fragment

MainActivity:

class MainActivity : AppCompatActivity(),ListFragment.OnFragmentInteractionListener {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.main_activity)


        var viewModel = ViewModelProvider.NewInstanceFactory().create(TapupuViewModel::class.java)
        viewModel.setData(movieList)
    }
    }

ViewModel:

class TapupuViewModel : ViewModel() {

    val message  = MutableLiveData<ArrayList<Movie>>()

    fun setData(msg:ArrayList<Movie>){
        message.setValue(msg)
    }
}

Fragment:

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,savedInstanceState: Bundle?): View? {
        val view = inflater.inflate(R.layout.fragment_list2, container, false)

        val model = ViewModelProvider(activity!!).get(TapupuViewModel::class.java)
        model.message.observe(viewLifecycleOwner, Observer {
            it?.let {
                moviesArrayList = it

            }
        })
        }

I am probably doing something wrong there. Can you please help me?

Answer 1

View <---> ViewModel <---> Repository <---> Room Dao

The view is: Fragment/Activity

No need to share any ViewModels or ... between your Activity and Fragments.

class MyRepository {
    private val dao: YourDao = ...

    fun getModelFromLocal(): LiveData/RxJava/List<Model> = dao.getModel()
}

In your ViewModel

private val repository: MyRepository  = ...
val resultLiveData = MutableLiveData<SomeModelToShowOnUI>()

fun onUISentEventToLoadData() {
    val data: SomeModelToShowOnUI = repository.getModelFromLocal()
    resultLiveData.value = data
}

Activity/Fragment observe changes from ViewModel:

class MyFragment : Fragment() {
    override fun onViewCreated() {
        resultLiveData.observe(this, Observer {
            //update UI
        })
    }
}

Each Fragment/Activity has its own implementation.