android - How to set target fragment of a dialog when using navigation components

Question

I'm showing a dialog inside a fragment using childFragmentManager or within an Activity using the supportFragmentManager, in the process I would like to set the target fragment, like this:

val textSearchDialog = TextSearchDialogFragment.newInstance()
textSearchDialog.setTargetFragment(PlaceSearchFragment@this, 0)

But when running that code I get the error:

java.lang.IllegalStateException: Fragment TextSearchDialogFragment{b7fce67 #0 0} declared target fragment PlaceSearchFragment{f87414 #0 id=0x7f080078} that does not belong to this FragmentManager!

I don't know how to access the FragmentManager the navigation components are using to manage the showing of the fragment, is there a solution for this?

Answer 1

Update: as part of Navigation 2.3.0, Navigation adds explicit support for returning a result with a specific section on returning a result from a Dialog destination as an alternative to using a shared ViewModel.

Previous answer:

The recommended pattern for communicating between Fragments with the Navigation Architecture Components is via a shared ViewModel - a ViewModel that lives at the Activity level achieved by retrieving the ViewModel using ViewModelProvider(getActivity())

As per the documentation, this offers a number of benefits:

• The activity does not need to do anything, or know anything about this communication.
• Fragments don't need to know about each other besides the SharedViewModel contract. If one of the fragments disappears, the other one keeps working as usual.
• Each fragment has its own lifecycle, and is not affected by the lifecycle of the other one. If one fragment replaces the other one, the UI continues to work without any problems.

You can also share ViewModels at a smaller scope than your whole activity by using a navigation graph scoped ViewModel.