问单个活动:带有AppBarLayout的片段

EN

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    fun setupActionBar(toolbar: Toolbar) {
        setSupportActionBar(toolbar)
        val navHostFragment =
            supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
        val navController = navHostFragment.navController
        val appBarConfiguration = AppBarConfiguration.Builder(
            R.id.fragment, R.id.fragment_b
        ) .build()

        NavigationUI.setupActionBarWithNavController(
            this,
            mNavController,
            navController
        )
    }

}

class FragmentA : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = inflater.inflate(R.layout.fragment_a, container, false)

        (requireActivity() as MainActivity).setupActionBar(view.findViewById(R.id.fragment_toolbar))


        return view
    }

}

class FragmentB : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = inflater.inflate(R.layout.fragment_b, container, false)

        (requireActivity() as MainActivity).setupActionBar(view.findViewById(R.id.fragment_toolbar))


        return view
    }

}