Android Navigation - Can't change toolbar title after setting the nav graph manually

Question

Following those answers, I've been setting my nav graph manually since I can have different startDestinations depending on some conditions. There is a collapsing toolbar as well.

The activity code:

class FlowActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_product_flow)
        setSupportActionBar(toolbar as Toolbar)
        supportActionBar?.apply {
            setDisplayHomeAsUpEnabled(true)
            setDisplayShowHomeEnabled(true)
        }
        val tspType = intent.getSerializableExtra(Const.TSP_EXTRA) as TspType

        val navHost =
            supportFragmentManager.findFragmentById(R.id.host_fragment) as NavHostFragment?
        val navController = navHost!!.navController
        val navInflater = navController.navInflater
        val graph = navInflater.inflate(R.navigation.product_flow_nav)

        when (tspType) {
            TspType.TAXI -> {
                graph.startDestination = R.id.taxiSearchFragment
            }
            TspType.CAR_RENTAL -> {
                graph.startDestination = R.id.rentalSearchFragment
            }
            else -> {
                graph.startDestination = R.id.productSelectionFragment
            }
        }
        navController.graph = graph

        navController.addOnDestinationChangedListener { _, newDest, _ ->
            app_bar_layout.setExpanded(true)

            title = when (newDest.id) {
                R.id.rentalSearchFragment -> "Rent a car"
                R.id.taxiSearchFragment -> "Book a taxi"
                R.id.productSelectionFragment -> "${tspType.productName} products"
                R.id.activationFragment -> "Activate ${tspType.productName}"
                else -> "else title"
            }
        }

        val appBarConfiguration = AppBarConfiguration(setOf(), null) { onSupportNavigateUp() }
        setupActionBarWithNavController(navController, appBarConfiguration)
        collapsing_toolbar.setupWithNavController(toolbar, navController, appBarConfiguration)
    }

    override fun onSupportNavigateUp(): Boolean {
        val navController = Navigation.findNavController(this, R.id.host_fragment)
        if (navController.currentDestination?.id == R.id.taxiSearchFragment || navController.currentDestination?.id == R.id.rentalSearchFragment || navController.currentDestination?.id == R.id.productSelectionFragment) {
            finish()
        }
        return navController.navigateUp() || super.onSupportNavigateUp()
    }
}

I don't think there is anything special, but the first fragment will have it's title set no problem. But after that every set title are not working and the first title remains.

The navigation xml does not contains any label property. I've tried already :

• title = "xxx"
• supportActionBar.title = "xxx"
• toolbar.title = "xxx"

Maybe something is in the wrong order but I can't figure out why or what's wrong.