Provide a way to handle navigating back and forth between NavHostFragments embedded within other NavHostFragments (or if it's already available, document how to do) [120690961]

Fixed

Feature Request

Status Update

No update yet.

Description

je...@23andme.com

created issue #1

Dec 9, 2018 03:07AM

Component used: Navigation
Version used: 1.0.0-alpha08
Devices/Android versions reproduced on:

Assuming:
- Main Activity has a NavHostFragment, which navigates between Fragment A & Fragment B
- Main activity handles going back with onSupportNavigateUp
- Fragment B has it's own NavHostFragment, which navigated between InnerFragmentB1 & InnerFragmentB2
- Parent NavHostFragment navigates from A -> B (which starts with B1)
- Sub NavHostFragment navigates from B1 -> B2
- Press up: Sub NavHostFragment returns to B1
- Press up: Parent NavHostFragment returns from B to A

What's the proper way of handling these types of situations where we'd like the back button to handle backing out of Inner Fragments first and then Outer Fragments after?

Details here:

https://stackoverflow.com/q/53688934/1229936
Sample Code:

https://github.com/jeffreyfhow/NestedNavFragmentsTest

Comments

so...@gmail.com <so...@gmail.com> #2Dec 9, 2018 07:33AM

Yes, we need better control over Nested NavHost. Also, nested NavHostFragment is recreating and it can't hold it's last state.
Suppose:
- Main Activity has a NavHostFragment and it is set up with bottomNavigationView
- Each Fragment has multiple fragments.

Then what's the proper way of handling these types of situations?

il...@google.com <il...@google.com> #3Dec 10, 2018 05:58PM

Re #2 - supporting multiple back stacks for cases like bottom nav is being tracked in

https://issuetracker.google.com/issues/80029773 - please star that issue for updates.

il...@google.com <il...@google.com> Dec 10, 2018 09:55PM

Accepted by il...@google.com.

il...@google.com <il...@google.com> #4Dec 14, 2018 12:05AM

Marked as fixed.

https://android-review.googlesource.com/846338 adds a setFallbackOnNavigateUpListener method on AppBarConfiguration that allows you to register an OnNavigateUpListener to handle cases where navController.navigateUp() return false.

This allows you to solve your problem by:
- Adding your Toolbar to Fragment B
- Call:
toolbar.setupWithNavController(innerNavController, AppBarConfiguration(setOf()) {
findNavController().navigateUp()
})

By using an empty set of top level destinations, the Up button will always appear. When the innerNavController is on its own start destination, the fallback will be called, allowing you to pass the navigateUp() call to the outer NavController. The reason the Toolbar in your FragmentB is the right place to do this is so that it has a reference to both your inner NavController and a reference to your outer NavController.

This will be available in 1.0.0-alpha09.

See also the related issue for activities:

https://issuetracker.google.com/issues/79993862

ka...@gmail.com <ka...@gmail.com> #5Dec 27, 2018 05:06PM

Re #4 - In my use case I have single activity and single (global) toolbar setup with it. So it doesn't make sense for my application to add additional toolbar for my nested fragments. I just want to work them with existing activity's toolbar. I would like to use nested fragments to use ViewModels shared with parentFragment. Can you consider supporting my use case?

Issue 120690961