ViewModel refetches data when fragment is recreated

Question

I am using Bottom Navigation with Navigation Architecture Component. When the user navigates from one item to another(via Bottom navigation) and back again view model call repository function to fetch data again. So if the user goes back and forth 10 times the same data will be fetched 10 times. How to avoid re-fetching when the fragment is recreated data is already there?.

Fragment

class HomeFragment : Fragment() {

    @Inject
    lateinit var viewModelFactory: ViewModelProvider.Factory

    private lateinit var productsViewModel: ProductsViewModel
    private lateinit var productsAdapter: ProductsAdapter

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_home, container, false)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        initViewModel()
        initAdapters()
        initLayouts()
        getData()
    }

    private fun initViewModel() {
        (activity!!.application as App).component.inject(this)

        productsViewModel = activity?.run {
            ViewModelProviders.of(this, viewModelFactory).get(ProductsViewModel::class.java)
        }!!
    }

    private fun initAdapters() {
        productsAdapter = ProductsAdapter(this.context!!, From.HOME_FRAGMENT)
    }

    private fun initLayouts() {
        productsRecyclerView.layoutManager = LinearLayoutManager(this.activity)
        productsRecyclerView.adapter = productsAdapter
    }

    private fun getData() {
        val productsFilters = ProductsFilters.builder().sortBy(SortProductsBy.NEWEST).build()

        //Products filters
        productsViewModel.setInput(productsFilters, 2)

        //Observing products data
        productsViewModel.products.observe(viewLifecycleOwner, Observer {
            it.products()?.let { products -> productsAdapter.setData(products) }
        })

        //Observing loading
        productsViewModel.networkState.observe(viewLifecycleOwner, Observer {
            //Todo showing progress bar
        })
    }
}

ViewModel

class ProductsViewModel
@Inject constructor(private val repository: ProductsRepository) : ViewModel() {

    private val _input = MutableLiveData<PInput>()

    fun setInput(filters: ProductsFilters, limit: Int) {
        _input.value = PInput(filters, limit)
    }

    private val getProducts = map(_input) {
        repository.getProducts(it.filters, it.limit)
    }

    val products = switchMap(getProducts) { it.data }
    val networkState = switchMap(getProducts) { it.networkState }
}

data class PInput(val filters: ProductsFilters, val limit: Int)

Repository

@Singleton
class ProductsRepository @Inject constructor(private val api: ApolloClient) {

    val networkState = MutableLiveData<NetworkState>()

    fun getProducts(filters: ProductsFilters, limit: Int): ApiResponse<ProductsQuery.Data> {
        val products = MutableLiveData<ProductsQuery.Data>()

        networkState.postValue(NetworkState.LOADING)

        val request = api.query(ProductsQuery
                .builder()
                .filters(filters)
                .limit(limit)
                .build())

        request.enqueue(object : ApolloCall.Callback<ProductsQuery.Data>() {
            override fun onFailure(e: ApolloException) {
                networkState.postValue(NetworkState.error(e.localizedMessage))
            }

            override fun onResponse(response: Response<ProductsQuery.Data>) = when {
                response.hasErrors() -> networkState.postValue(NetworkState.error(response.errors()[0].message()))
                else -> {
                    networkState.postValue(NetworkState.LOADED)
                    products.postValue(response.data())
                }
            }
        })

        return ApiResponse(data = products, networkState = networkState)
    }
}

Navigation main.xml

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/mobile_navigation.xml"
    app:startDestination="@id/home">

    <fragment
        android:id="@+id/home"
        android:name="com.nux.ui.home.HomeFragment"
        android:label="@string/title_home"
        tools:layout="@layout/fragment_home"/>
    <fragment
        android:id="@+id/search"
        android:name="com.nux.ui.search.SearchFragment"
        android:label="@string/title_search"
        tools:layout="@layout/fragment_search" />
    <fragment
        android:id="@+id/my_profile"
        android:name="com.nux.ui.user.MyProfileFragment"
        android:label="@string/title_profile"
        tools:layout="@layout/fragment_profile" />
</navigation>

ViewModelFactory

@Singleton
class ViewModelFactory @Inject
constructor(private val viewModels: MutableMap<Class<out ViewModel>, Provider<ViewModel>>) : ViewModelProvider.Factory {

    @Suppress("UNCHECKED_CAST")
    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        val creator = viewModels[modelClass]
                ?: viewModels.asIterable().firstOrNull { modelClass.isAssignableFrom(it.key) }?.value
                ?: throw IllegalArgumentException("unknown model class $modelClass")
        return try {
            creator.get() as T
        } catch (e: Exception) {
            throw RuntimeException(e)
        }
    }
}

Answer 1

One simple solution would be to change the ViewModelProvider owner from this to requireActivity() in this line of code:

ViewModelProviders.of(this, viewModelFactory).get(ProductsViewModel::class.java)

Therefore, as the activity is the owner of the viewmodel and the lifcycle of viewmodel attached to the activity not to the fragment, navigating between fragments within the activity won't recreated the viewmodel.