导航组件-处理多个堆栈的后退行为

Question

我的主要问题是后退按钮（设备按钮）无法像findNavController().navigateUp()一样正常工作。

我具有以下结构。

主导航图：

Login -> Home, here FlowA and FlowB are loaded in DrawerLayout

HomeFragment代码：

class HomeFragment : Fragment() {
    private var _binding: FragmentHomeBinding? = null
    private val binding get() = _binding!!
    private val viewModel: HomeViewModel by activityViewModels()
    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        _binding = FragmentHomeBinding.inflate(inflater, container, false)
        val flow1Nav = NavHostFragment.create(R.navigation.flow_a)
        val flow2Nav = NavHostFragment.create(R.navigation.flow_b)
        childFragmentManager.beginTransaction()
            .add(R.id.flContent, flow1Nav, flow1Nav.javaClass.name)
            .add(R.id.flContent, flow2Nav, flow2Nav.javaClass.name)
            .show(flow1Nav)
            .hide(flow2Nav)
            .commitNow()
        binding.navView.findViewById<LinearLayout>(R.id.ll_flow1).setOnClickListener {
            binding.drawerLayout.closeDrawers()
            childFragmentManager.beginTransaction()
                .show(flow1Nav)
                .hide(flow2Nav)
                .commit()
        }
        binding.navView.findViewById<LinearLayout>(R.id.ll_flow2).setOnClickListener {
            binding.drawerLayout.closeDrawers()
            childFragmentManager.beginTransaction()
                .show(flow2Nav)
                .hide(flow1Nav)
                .commit()
        }
    }
}

fragment_home.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Use DrawerLayout as root container for activity -->
<androidx.drawerlayout.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <FrameLayout
            android:id="@+id/flContent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
    </LinearLayout>
    <!-- Container for contents of drawer - use NavigationView to make configuration easier -->
    <com.google.android.material.navigation.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="false">
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">
            <include layout="@layout/drawer_header" />
            <include layout="@layout/drawer_menu" />
        </LinearLayout>
    </com.google.android.material.navigation.NavigationView>

</androidx.drawerlayout.widget.DrawerLayout>

流导航图

流量B导航图

问题

1. 为什么findNavController().navigateUp()正常工作，而设备后退按钮却不能正常工作？
2. 多个堆栈（导航图）破坏了导航系统？

所有源代码都可以找到here。

Answer 1

我找到了一个工作环境

requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner) {
   findNavController().navigateUp()
}