Remove up button from action bar when navigating using BottomNavigationView with Android Navigation UI library

Starting with 1.0.0-alpha07 you can use AppBarConfiguration to configure that behaviour.

AppBarConfiguration has a Builder constructor so you can create a new Builder with a specific set of top level destinations, referenced by their id (this id is the one you set on your navigation layout).

Create new AppBarConfiguration:

val appBarConfiguration = AppBarConfiguration
            .Builder(
                    R.id.navigationHomeFragment,
                    R.id.navigationListFragment,
                    R.id.navigationProfileFragment)
            .build()

Then, instead of setupActionBarWithNavController(this, navController) you need to call setupActionBarWithNavController(this, navController, appBarConfiguration)

This is the right way to handle top navigation behaviours.

I had the same problem and I found a way to get the current fragment with the NavController.addOnNavigatedListener, so I applied the following logic within my Activity and for now it works for me

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_home)
    val navHost = supportFragmentManager
            .findFragmentById(R.id.navHostFragment) as NavHostFragment

    navHost.navController.addOnNavigatedListener { _, destination ->
        val showButton = showUpButton(destination.id)
        //Here occurs the magic
        supportActionBar?.setDisplayShowHomeEnabled(showButton)
        supportActionBar?.setDisplayHomeAsUpEnabled(showButton)
    }
}

//Check according to your convenience which fragment id
//should show or hide the "Up Button"
private fun showUpButton(id: Int): Boolean {
    return id != R.id.your_home_fragment && id != R.id.your_list_fragment 
            && id != R.id.your_profile_fragment
}

And this is my project...

I do not know if it is the best option but if someone has any better suggestion, it will be welcome

Use this instead of setupWithNavController:

navController.addOnNavigatedListener(new NavController.OnNavigatedListener() {
     @Override
     public void onNavigated(@NonNull NavController controller, @NonNull NavDestination destination) {
         toolbar.setTitle(destination.getLabel());
     }
});

Or the equivalent in Kotlin.

The only thing setupWithNavController does is add a listener to change the toolbar title, and creates the up button. If you don't want the up button, just add a listener which changes the toolbar title only.