与底部导航栏android一起使用导航时，片段已添加的问题

Question

我有一个底部导航视图，该视图已在androidx导航中实现，但问题是它向我显示了[]的错误>

java.lang.IllegalStateException: Fragment already added: BaseFragment{27d5b00 (2156a830-7756-4fc9-bc63-7c6f3d6705f0) id=0x7f08008c android:switcher:2131230860:0}
我有一个基本片段，可提供不同片段的视图

class MainActivity : AppCompatActivity(),
        ViewPager.OnPageChangeListener,
        BottomNavigationView.OnNavigationItemReselectedListener,
        BottomNavigationView.OnNavigationItemSelectedListener {


    // overall back stack of containers
    private val backStack = Stack<Int>()

    // list of base destination containers
    private val fragments = listOf(
            BaseFragment.newInstance(R.layout.content_home_base, R.id.toolbar_home, R.id.nav_host_home),
            BaseFragment.newInstance(R.layout.content_library_base, R.id.toolbar_library, R.id.nav_host_library),
            BaseFragment.newInstance(R.layout.content_settings_base, R.id.toolbar_settings, R.id.nav_host_settings))


    // map of navigation_id to container index
    private val indexToPage = mapOf(0 to R.id.home, 1 to R.id.library, 2 to R.id.settings)

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

        // setup main view pager
        main_pager.addOnPageChangeListener(this)
        main_pager.adapter = ViewPagerAdapter()
        main_pager.post(this::checkDeepLink)
        main_pager.offscreenPageLimit = fragments.size

        // set bottom nav
        bottom_nav.setOnNavigationItemSelectedListener(this)
        bottom_nav.setOnNavigationItemReselectedListener(this)


        // initialize backStack with elements
        if (backStack.empty()) backStack.push(0)
    }

    /// BottomNavigationView ItemSelected Implementation
    override fun onNavigationItemSelected(item: MenuItem): Boolean {
        val position = indexToPage.values.indexOf(item.itemId)
        if (main_pager.currentItem != position) setItem(position)
        return true
    }

    override fun onNavigationItemReselected(item: MenuItem) {
        val position = indexToPage.values.indexOf(item.itemId)
        val fragment = fragments[position]
        fragment.popToRoot()
    }

    override fun onBackPressed() {
        val fragment = fragments[main_pager.currentItem]
        val hadNestedFragments = fragment.onBackPressed()
        // if no fragments were popped
        if (!hadNestedFragments) {
            if (backStack.size > 1) {
                // remove current position from stack
                backStack.pop()
                // set the next item in stack as current
                main_pager.currentItem = backStack.peek()

            } else super.onBackPressed()
        }
    }

    /// OnPageSelected Listener Implementation
    override fun onPageScrollStateChanged(state: Int) {}

    override fun onPageScrolled(p0: Int, p1: Float, p2: Int) {}

    override fun onPageSelected(page: Int) {
        val itemId = indexToPage[page] ?: R.id.home
        if (bottom_nav.selectedItemId != itemId) bottom_nav.selectedItemId = itemId
    }

    private fun setItem(position: Int) {
        main_pager.currentItem = position
        backStack.push(position)
    }

    private fun checkDeepLink() {
        fragments.forEachIndexed { index, fragment ->
            val hasDeepLink = fragment.handleDeepLink(intent)
            if (hasDeepLink) setItem(index)
        }
    }

    inner class ViewPagerAdapter : FragmentPagerAdapter(supportFragmentManager) {

        override fun getItem(position: Int): Fragment = fragments[position]

        override fun getCount(): Int = fragments.size

    }
}
基本片段类：

class BaseFragment: Fragment() {

    private val defaultInt = -1
    private var layoutRes: Int = -1
    private var toolbarId: Int = -1
    private var navHostId: Int = -1
    private val appBarConfig = AppBarConfiguration(rootDestinations)


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            layoutRes = it.getInt(KEY_LAYOUT)
            toolbarId = it.getInt(KEY_TOOLBAR)
            navHostId = it.getInt(KEY_NAV_HOST)

        } ?: return
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        // Inflate the layout for this fragment
        return if (layoutRes == defaultInt) null
        else inflater.inflate(layoutRes, container, false)
    }

    override fun onStart() {
        super.onStart()
        // return early if no arguments were parsed
        if (toolbarId == defaultInt || navHostId == defaultInt) return

        // setup navigation with toolbar
        val toolbar = requireActivity().findViewById<Toolbar>(toolbarId)
        val navController = requireActivity().findNavController(navHostId)

        NavigationUI.setupWithNavController(toolbar, navController, appBarConfig)

//        NavigationUI.setupWithNavController(toolbar,navController)
    }

    fun onBackPressed(): Boolean {
        return requireActivity()
                .findNavController(navHostId)
                .navigateUp(appBarConfig)
    }


    fun popToRoot() {
        val navController = requireActivity().findNavController(navHostId)
        navController.popBackStack(navController.graph.startDestination, false)
    }

    fun handleDeepLink(intent: Intent) = requireActivity().findNavController(navHostId).handleDeepLink(intent)


    companion object {

        private const val KEY_LAYOUT = "layout_key"
        private const val KEY_TOOLBAR = "toolbar_key"
        private const val KEY_NAV_HOST = "nav_host_key"

        fun newInstance(layoutRes: Int, toolbarId: Int, navHostId: Int) = BaseFragment().apply {
            arguments = Bundle().apply {
                putInt(KEY_LAYOUT, layoutRes)
                putInt(KEY_TOOLBAR, toolbarId)
                putInt(KEY_NAV_HOST, navHostId)
            }
        }
    }
}
我先尝试清空堆栈，但那没有用，我为三个viewpager元素/片段设置了三个navgraph。

我有一个底部导航视图，该视图已在androidx导航中实现，但问题是它向我显示了java.lang.IllegalStateException的错误：片段已添加：...

Answer 1

我们恢复到2.1.0（导航库），并且再次起作用