CODEWITHSUNDEEP
androidmvvmkotlinnavigationandroid-jetpack
C. Alen
C. Alen

Reputation: 214

How to prevent setting view model again, on back fragment navigation

I am using Android Jetpack Navigation, MVVM and dataBinding and I am facing one problem. Every time when I navigate back from details fragment, my main List fragment is refreshed (API is called again, and recyclerList is drawn again). How can I prevent this?

This is Main List Fragment code:

class PostListFragment : BaseFragment() {

private lateinit var viewModel: PostListViewModel

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {

    val binding = TestFragmentBinding.inflate(inflater, container, false)
    val factory = InjectorUtils.providePostListViewModelFactory()
    viewModel = ViewModelProviders.of(this, factory).get(PostListViewModel::class.java)

    val adapter = MainListAdapter()
    binding.mainList.adapter = adapter

    binding.let {
        it.viewmodel = viewModel
        it.setLifecycleOwner(this@PostListFragment)
    }

    subscribeUi(adapter)
    return binding.root
}

private fun subscribeUi(adapter: MainListAdapter) {

    viewModel.progressVisible.postValue(true)
    addToDisposable(viewModel.getContentRepository().getAllPosts(requireContext())
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe({ result ->
            viewModel.progressVisible.postValue(false)
            adapter.submitList(result)
        }, { error ->
            viewModel.progressVisible.postValue(false)
        }))
}

}

Also I have to add, that I am using this fragment on MainFragment which contains viewPager.

The code of my MainFragment:

class MainFragment : Fragment() {

private lateinit var sharedViewModel: SharedNewPostViewModel
private lateinit var viewModel: MainViewModel

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {

    val binding = MainFragmentBinding.inflate(inflater, container, false)

    val factory = InjectorUtils.provideMainViewModelFactory()
    viewModel = ViewModelProviders.of(this, factory).get(MainViewModel::class.java)

    binding.let {
        it.viewModel = viewModel
        it.setLifecycleOwner(this@MainFragment)
    }

    sharedViewModel = activity?.run {
        ViewModelProviders.of(this).get(SharedNewPostViewModel::class.java)
    } ?: throw Exception("Invalid activity")

    return binding.root
}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)

    val pagerAdapter = MainPagerAdapter(childFragmentManager)

    viewPager.adapter = pagerAdapter
    tabLayout.setupWithViewPager(viewPager)
}

}

Upvotes: 2

Views: 613

Answers (1)

Martin Zeitler
Martin Zeitler

Reputation: 76669

it is required to check the savedInstanceState in Activity.onCreate() already:

if(savedInstanceState == null) {
    ...
}

and when it's not null, do not inflate the Fragment - which subsequently will not call Fragment.onCreateView() twice (otherwise it's difficult to return a View from there).

Upvotes: 1

Related Questions