NavHostLayout.kt

  class NavHostLayout
  @JvmOverloads constructor(context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0):
      FrameLayout(context, attrs, defStyleAttr), NavHost {

    init {
      ...

      /* 1 */ navigationController = NavController(context)
      /* 2 */ Navigation.setViewNavController(this, navigationController)
      /* 3 */ val navigator = createControllerNavigator()
      /* 4 */ navigationController.navigatorProvider += navigator
      /* 5 */ navigationController.setGraph(graphId)
    }

    override fun getNavController(): NavController = navigationController
  }