getNavigationController.kt

private fun Fragment.getNavigationController(parent: Fragment? = null) : NavigationController? {
    if (parentFragment == null) return null
    if (parent == null) return getNavigationController(parentFragment)
    if (parentFragment!! is NavigationController) {
        return parentFragment as NavigationController
    }
    return getNavigationController(parentFragment)
}

val Fragment.navigationController : NavigationController? by lazy {
    getNavigationController(parentFragment)
}