How can I pass data to the first Fragment whilst using the Navigation Architecture?

Question

I'm trying to pass a bundle of object instances down from my main activity to the first fragment in a chain of other fragments using the NavHostFragment. I've tried all sorts but the bundle always seems to be null once it reaches the first fragment.

Here's how I'm initiating the NavHostFragment (frameContainer is a Frame Container element in my layout xml)

NavHostFragment navHost = NavHostFragment.create(R.navigation.claim_nav_graph);
getSupportFragmentManager().beginTransaction()
        .replace(R.id.frameContainer, navHost)
        .setPrimaryNavigationFragment(navHost)
        .commit();

The documentation says there are 2 different .create functions, one of them you can pass a second arguments to as a bundle, but Android Studio doesn't allow me to use this version.

Does anyone have any ideas?

Thanks in advance!

Answer 1

If you're using viewModels, you can do this:

your viewmodel:

class NiceViewModel: ViewModel() {

    var dataYouNeedToPass = "initialValue"

}

your activity:

class MainActivity : AppCompatActivity() {

    val niceViewModel: NiceViewModel by viewModels()

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

        niceViewModel.dataYouNeedToPass = "data You Need To Pass"

    }

}

your fragment:

class YourFragment : Fragment() {

    private lateinit var niceViewModel: NiceViewModel


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

        niceViewModel = (activity as MainActivity).niceViewModel
        niceViewModel.dataYouNeedToPass //do whatever you need to do with this
    
    }


}

Answer 2

It does seem to be a flaw with the NavHostFragment, passing data down to the first fragment does not seem to be possible, as the Bundle you can set as a second argument on the create function is overwritten along the way.

In the end I resolved this by building the bundle in the first fragment of the activity instead. I was able to access the activities intent properties using the below.

// Kotlin
activity.intent?.extras?.getBundle(KEY_BUNDLE_ID)
// Java
getActivity().getIntent().getBundleExtra(KEY_BUNDLE_ID)

This was enough of a workaround for me in this situation, but it would be great if it was possible