How to get fragments from backstack when using Android Navigation Component?

Question

How can I access any of the fragments in backstack when using Android Navigation Component? Let's sat you navigate to Fragment A then to Fragment B and then to Fragment C using Navigation Component. Now you want to access Fragment A or Fragment B instance (without popping any fragments) and set a value to one of its fields. Back in the day, we could do that using findFragmentByTag. But how can you do it now when using Navigation Component?

That isn't how you should be [communicating with fragments](https://developer.android.com/guide/fragments/communicate) at all. All of the techniques in the documentation work with the Navigation Component. — ianhanniballake, Sep 03 '21 at 02:24
@ianhanniballake Thank you for your comment and including the link. I believe that I had read this before, but they change the documents every damn day! There was some new things that I learned. Thanks again! — Harry, Sep 03 '21 at 19:19

score 1 · Answer 1 · answered Sep 03 '21 at 00:08

If you want to access the other fragments data in the same activity, using SharedViewModel might be a good idea. You can check the SharedViewModel example.

class SharedViewModel : ViewModel() {
    val selected = MutableLiveData<Item>()

    fun select(item: Item) {
        selected.value = item
    }
}

class ListFragment : Fragment() {

    private lateinit var itemSelector: Selector

    // Use the 'by activityViewModels()' Kotlin property delegate
    // from the fragment-ktx artifact
    private val model: SharedViewModel by activityViewModels()

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        itemSelector.setOnClickListener { item ->
            // Update the UI
        }
    }
}

class DetailFragment : Fragment() {

    // Use the 'by activityViewModels()' Kotlin property delegate
    // from the fragment-ktx artifact
    private val model: SharedViewModel by activityViewModels()

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        model.selected.observe(viewLifecycleOwner, Observer<Item> { item ->
            // Update the UI
        })
    }
}

If you want to see more detail, here is the official documentation for the SharedViewModel.

How to get fragments from backstack when using Android Navigation Component?

1 Answers1