NavigationActivity.kt

class NavigationActivity : AppCompatActivity() {
    private lateinit var fragmentContainer: ViewGroup
    private lateinit var navigationDelegate: NavigationDelegate


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        fragmentContainer = findViewById(R.id.fragment_container) as ViewGroup
        navigationDelegate = NavigationDelegate(supportFragmentManager, fragmentContainer.id)

        navigate(to = MasterFragment(), addToBackStack = false)
    }

    public fun navigate(from: Fragment? = null, to: Fragment, addToBackStack: Boolean = true) {
        navigationDelegate.navigate(from, to, addToBackStack)
    }
}