android - How to get a result from fragment using Navigation Architecture Component?

Question

Let's say that we have two fragments: MainFragment and SelectionFragment. The second one is build for selecting some object, e.g. an integer. There are different approaches in receiving result from this second fragment like callbacks, buses etc.

Now, if we decide to use Navigation Architecture Component in order to navigate to second fragment we can use this code:

NavHostFragment.findNavController(this).navigate(R.id.action_selection, bundle)

where bundle is an instance of Bundle (of course). As you can see there is no access to SelectionFragment where we could put a callback. The question is, how to receive a result with Navigation Architecture Component?

Answer 1

They have added a fix for this in the 2.3.0-alpha02 release.

If navigating from Fragment A to Fragment B and A needs a result from B:

findNavController().currentBackStackEntry?.savedStateHandle?.getLiveData<Type>("key")?.observe(viewLifecycleOwner) {result ->
    // Do something with the result.
}

If on Fragment B and need to set the result:

findNavController().previousBackStackEntry?.savedStateHandle?.set("key", result)

I ended up creating two extensions for this:

fun Fragment.getNavigationResult(key: String = "result") =
    findNavController().currentBackStackEntry?.savedStateHandle?.getLiveData<String>(key)

fun Fragment.setNavigationResult(result: String, key: String = "result") {
    findNavController().previousBackStackEntry?.savedStateHandle?.set(key, result)
}