Navigation Component: Navigate from Fragment in Viewpager to another Fragment

Question

I have a Fragment A which navigates to Fragment B

Fragment B hosts a ViewPager2.

ViewPager2 has two fragments inflated in it - Fragment C and Fragment D.

On clicking an item in Fragment C I want to navigate to a new instance of Fragment D on top of Fragment B.

Currently, my code is something like this -

findNavController().navigate(
            R.id.action_FragmentC_to_FragmentD,
            bundleOf("id" to id, "type" to "list")
        )

However, when I try to navigate I get the following exception -

java.lang.IllegalArgumentException: Navigation action/destination com.test.at:id/action_FragmentC_to_FragmentD cannot be found from the current destination Destination(com.krtkush.audiotime:id/FragmentB) label=FragmentB

From what I can understand is that the navigation component is still on Fragment B but I'm trying to navigate to Fragment D from Fragment C and hence it is throwing an exception.

I (think) can fix this by adding a listener which informs Fragment B when the item is tapped in Fragment C and then navigate to Fragment D from Fragment B. However, this will make my Fragment C tightly coupled to Fragment B which I don't want to. Anyway to fix this is another way?

Answer 1

If you do not navigate() to Fragment C and Fragment D, you will remain on the last destination you navigated to: Fragment B, that is the expected behavior. The NavController knows nothing about child fragments such as fragments within a ViewPager of Fragment B and therefore you were never on Fragment C as a destination.

If you never navigate() to Fragment C and it is only viewable as part of your ViewPager, then Fragment C should not be in your graph. Any actions from fragments within Fragment B's ViewPager should be actions on Fragment B directly (the destination you're actually on).

Note that you can reuse the same actions names on fragments such as Fragment D if you are also using them as standalone destinations in your graph (thus ensuring that the action is available in both cases).