问安卓导航组件如何保存BottomNavigationBar片段状态

EN

 bottomNavigationView = findViewById(R.id.bottom_nav)
        val navGraphIds = listOf(R.navigation.home, R.navigation.category, R.navigation.cart, R.navigation.account, R.navigation.jak)
        // Setup the bottom navigation view with a list of navigation graphs
        val controller = bottomNavigationView?.setupWithNavController(
                navGraphIds = navGraphIds,
                fragmentManager = supportFragmentManager,
                containerId = R.id.nav_host_container,
                intent = intent
        )

        // Whenever the selected controller changes, setup the action bar.
        controller?.observe(this, Observer { navController ->
            setupActionBarWithNavController(navController)
        })
        currentNavController = controlle

implementation "androidx.navigation:navigation-fragment:2.2.0-alpha03"
implementation "androidx.navigation:navigation-ui:2.2.0-alpha03"
implementation "androidx.navigation:navigation-fragment-ktx:2.2.0-alpha03"
implementation "androidx.navigation:navigation-ui-ktx:2.2.0-alpha03"

@Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                             @Nullable Bundle savedInstanceState) {
        mViewModel = ViewModelProviders.of(this).get(HomePageViewModel.class);
        binding = DataBindingUtil.inflate(inflater, R.layout.home_page_fragment, container, false);
        binding.setLifecycleOwner(this);
        mViewModel.init();
        binding.setViewModel(mViewModel);
        setHasOptionsMenu(true);
        ((MainActivity) getActivity()).homeToolbarWithImage();
        ShowMainList();
        binding.swiperefresh.setOnRefreshListener(this);
        return binding.getRoot();
    }