I keep the user as MutableLiveData in a shared ViewModel and observe that in the activity:

viewModel.user.observe(this) {
    if (it == null) {
        val action = LoginDirections.actionGlobalLogin()
        navController.navigate(action)
    }
}

when the user is null (I am logged out) I navigate to the login/signup sub nav graph

To avoid going back to the previous screen without logging in I handle onBackPressed for the login screen manually:

override fun onBackPressed() {
    if (navController.currentDestination?.id == R.id.loginFragment) {
        finish()
    } else {
        super.onBackPressed()
    }
}

in both the login and signup fragments I observe the same User in the shared ViewModel as I do in the activity, and just pop the backstack if it changes from null to an actual value ( = we are signed in)

userViewModel.user.observe(viewLifecycleOwner) {
    if (it != null) {
        findNavController().popBackStack()
        binding.editTextEmail.clearFocus()
        binding.editTextPassword.clearFocus()
    }
}

they trigger it when the user navigates to the ProfileFragment

We talked about exactly this case and why it is required in the Navigating Navigation video:

so there is no way to set it once in the activity and then forget about it?

but still, it sounds very verbose to me to implement all this logic for every fragment that needs auth in my app

my approach works on the activity level

but I have to override onBackPressed to handle back for the login and signup screen properly

it's great that Google's team is that responsive

the one where we pop up to

LiveData gets a value as soon as we call

observe

, right?

It works if I use currentBackStackEntry as the lifecycle owner as described in the documentation. But in the video above you're using viewLifeCycleOwner which triggers right away. Am I missing something?

and the approach from the docs crashes when we rotate the screen with "IllegalStateException: NavController is not available before onCreate()"

I know how to fix the problem with accessing the navController in onCreate, I'm just wondering if I'm doing something wrong because neither the tutorial in the docs nor the one from the video works for me without modifications

And the docs work fine if you are using

FragmentContainerView

, which has been the recommended approach for quite some time. It sounds like you are still using

<fragment>

but thanks for the link!

it works now with fragment 1.3.0-beta01 👍

now that all the code is

onViewCreated

it looks like it could make sense to create an extension function for all fragments that need authentication

The LiveData that triggers the navigation to the login flow in the first place, it is also triggered when you press back while

LOGIN_SUCCESSFUL

is still false. Is this expected behavior? You don't notice it if you immediately move to another destination without an animation, but you can see it if you for example when you finish the activity. In this case, the input fields become empty because you are navigating to the login fragment again for a split second.

This approach from the Codelab handles back in a much simpler way, and it says "last updated October 2020": https://codelabs.developers.google.com/codelabs/advanced-android-kotlin-training-login-navigation#5

here the LoginFragment handles the back button itself (without a

LOGIN_SUCCESSFUL

flag). Is there anything wrong with this approach?