Jetpack Navigation 2.4+多返回栈下嵌套BottomNavigationView崩溃问题

将Navigation组件从2.3.5版本升级到2.4.2版本后，触发崩溃报错：
java.lang.IllegalArgumentException: No destination with ID XXX is on the NavController's back stack. The current destination is null
复现路径：FirstFragment → 携带独立BottomNavigationView的SecondFragment → ThirdFragment → 返回SecondFragment时触发崩溃。

现有实现逻辑 #

项目中存在两个搭载BottomNavigationView的Fragment容器：

• 主底部导航容器MainBottomNavFragment
  对应Fragment代码：

class MainBottomNavFragment : Fragment() {

    private lateinit var navController: NavController

    override fun onStart() {
        super.onStart()
        if (!::navController.isInitialized) {
            navController =
                Navigation.findNavController(requireActivity(), R.id.mainBottomNavHostFragment)
        }
        binding.bottomNavigation.setupWithNavController(navController)
    }
}

对应布局代码：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <fragment
        android:id="@+id/mainBottomNavHostFragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:defaultNavHost="false"
        app:layout_constraintBottom_toTopOf="@+id/bottomNavigation"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/main_menu_nav_graph" />

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottomNavigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:menu="@menu/main_menu" />

</androidx.constraintlayout.widget.ConstraintLayout>

主导航图main_menu_nav_graph配置：

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/main_bottom_nav_graph"
    app:startDestination="@id/first">

    <fragment
        android:id="@+id/first"
        android:name=".FirstFragment"
        android:label="FirstFragment" />

    <fragment
        android:id="@+id/second"
        android:name=".SecondFragment"
        android:label="SecondFragment" />

    <fragment
        android:id="@+id/third"
        android:name=".ThirdFragment"
        android:label="ThirdFragment">
        <action
        ... />
    </fragment>

    <navigation
        android:id="@+id/fourth"
        app:startDestination="@id/fourthFragment">

        <fragment
            android:id="@+id/fourthFragment"
            android:name=".FourthFragment"
            android:label="FourthFragment" />
        <fragment
            android:id="@+id/fourthFragmentA"
            android:name=".FourthFragmentA"
            android:label="FourthFragmentA" />
        <fragment
            android:id="@+id/fourthFragmentB"
            android:name=".FourthFragmentB"
            android:label="FourthFragmentB" />
    </navigation>
</navigation>

• 二级底部导航容器SecondFragment
  对应Fragment代码：

class SecondFragment : Fragment() {

    private lateinit var navController: NavController

    override fun onStart() {
        super.onStart()

        if (!::navController.isInitialized) {
            navController = Navigation.findNavController(requireActivity(), R.id.secondHostFragment)
            val inflater = navController.navInflater
            navController.setGraph(inflater.inflate(R.navigation.second_nav_graph), arguments)
        }
        binding.secondBottomNavigation.setupWithNavController(navController)
    }
}

对应布局代码：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/secondBottomNavigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        app:menu="@menu/second_menu" />

    <fragment
        android:id="@+id/secondHostFragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/secondBottomNavigation" />

</androidx.constraintlayout.widget.ConstraintLayout>

二级导航图second_nav_graph配置：

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/second_nav_graph"
    app:startDestination="@id/secondA">

    <fragment
        android:id="@+id/secondA"
        android:name=".SecondA"
        android:label="SecondA">
        <action
        ... />
    </fragment>
    <fragment
        android:id="@+id/secondB"
        android:name=".SecondB"
        android:label="SecondB" />
</navigation>

双层嵌套BottomNavigationView是否支持？ #

支持，但必须遵循Navigation组件的作用域规则，每个NavHostFragment必须和对应的NavController绑定在正确的生命周期作用域内，不能跨作用域查找、持有NavController实例。

版本升级后崩溃原因 #

2.4.0及以上版本Navigation组件收紧了NavController状态校验逻辑，修复了旧版本中跨作用域持有NavController不会触发异常的漏洞，崩溃来自两个实现错误：

1. 跨作用域查找NavController：在SecondFragment中通过Activity查找内部secondHostFragment对应的NavController，当SecondFragment被压入返回栈、视图销毁重建后，跨层级获取的NavController实例已和当前重建的NavHostFragment解绑，内部返回栈状态被清空，直接触发current destination为null的异常。2.3.5版本未对该状态做严格校验，因此不会崩溃，但该写法本身不符合Navigation的作用域设计规范。
2. 重复绑定导航栏：在onStart生命周期中重复调用setupWithNavController，未随视图销毁解绑监听器，Fragment从返回栈恢复到前台时，失效的监听器持有旧的NavController引用，状态恢复或导航操作时就会抛出找不到目标目的地的异常。
3. 重复设置导航图：代码中动态调用setGraph设置导航图，和xml中配置的navGraph属性冲突，会导致返回栈被意外重置。

修复方案 #

1. 所有Fragment内部嵌套的NavHostFragment，不要从Activity层级查找NavController，直接从当前Fragment的childFragmentManager获取实例：

// SecondFragment中替换原有初始化逻辑
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    val navHostFragment = childFragmentManager.findFragmentById(R.id.secondHostFragment) as NavHostFragment
    navController = navHostFragment.navController
    // 仅在视图创建时绑定一次导航栏
    binding.secondBottomNavigation.setupWithNavController(navController)
}

2. 将setupWithNavController绑定逻辑从onStart移动到onViewCreated中，和视图生命周期保持一致，避免重复绑定。
3. 删除代码中动态调用setGraph的逻辑，直接在secondHostFragment的xml布局中配置app:navGraph="@navigation/second_nav_graph"即可，避免重复设置导航图清空返回栈。
4. 主容器MainBottomNavFragment中的NavController初始化逻辑建议做同样修改，避免其他场景触发同类异常。

内容的提问来源于stack exchange，提问作者Milan Jiříček