bottomNavigationView

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottomNavigationView)
        val navController = findNavController(R.id.fragmentContainerView)

//        val appBarConfiguration = AppBarConfiguration(setOf(R.id.a1, R.id.a2, R.id.a3))
//        setupActionBarWithNavController(navController, appBarConfiguration)

        bottomNavigationView.setupWithNavController(navController)

    }

}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <fragment
        android:id="@+id/fragmentContainerView"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/my_nav"
        android:layout_marginBottom="60dp" />

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottomNavigationView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:menu="@menu/bottom_menu"/>


</androidx.constraintlayout.widget.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item
        android:id="@+id/a1"
        android:title="1"
        android:icon="@drawable/ic_launcher_foreground"
        />
    <item
        android:id="@+id/a2"
        android:title="2"
        android:icon="@drawable/ic_launcher_foreground"
        />
    <item
        android:id="@+id/a3"
        android:title="3"
        android:icon="@drawable/ic_launcher_foreground"
        />

</menu>