Adapter点击调用findNavController()切换Fragment后报错的解决方法

我在导航功能上遇到问题：存在一个包含RecyclerView的Fragment A（RecipeListingFragment），当导航跳转到Fragment B（RecipeDetailFragment）后返回A时，RecyclerView的Item点击会抛出错误View androidx.constraintlayout.widget.ConstraintLayout{1f8e1b2 V.E...... ........ 0,0-1080,1823} does not have a NavController set；但停留在A时功能正常。我的Adapter的onItemClicked方法中调用了findNavController()。

注：我非英语母语者，英文水平有限，这是首次提问。

相关代码见下文：

MainActivity代码 #

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainMenuBinding
    private lateinit var bottomNav: BottomNavigationView
    private lateinit var navController: NavController
    val authViewModel: AuthViewModel by viewModels()

    val TAG: String = "ReceitaListingFragment"


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        startUI()
    }

    private fun setNavController(){
        val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host) as NavHostFragment
        navController = navHostFragment.navController
        setupWithNavController(bottomNav,navController)
    }

    private fun startUI() {

        binding = ActivityMainMenuBinding.inflate(layoutInflater)
        setContentView(binding.root)
        bottomNav = findViewById(R.id.bottomNavigationView)
        setNavController()
        bottomNav.setOnItemSelectedListener {
            when (it.itemId){
                R.id.recipes -> {
                    val connected_to_internet:Boolean = isOnline(this)
                    val fragment:Fragment = RecipeListingFragment()
                    fragment.arguments = Bundle().apply {
                        putBoolean("connectivity",connected_to_internet)
                    }
                    replaceFragment(RecipeListingFragment())
                }
                R.id.profile -> replaceFragment(ProfileFragment())
            }
            true
        }

    }
    

    private fun replaceFragment(fragment : Fragment){

        val fragmentManager = supportFragmentManager
        val fragmentTransaction = fragmentManager.beginTransaction()
        fragmentTransaction.replace(R.id.nav_host,fragment)
        fragmentTransaction.commit()
    }
}

main_activity.xml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"
    tools:context=".MainActivity">


    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@+id/bottomNavigationView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/app_navigation" />

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottomNavigationView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="#E3E3E4"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:itemIconTint="@color/bordeux"
        app:itemTextColor="@color/bordeux"
        app:menu="@menu/bottom_nav_menu" />

</androidx.constraintlayout.widget.ConstraintLayout>

RecipeListingFragment中Adapter初始化代码 #

private val adapter by lazy {
    RecipeListingAdapter(
        onItemClicked = {pos,item ->

            findNavController().navigate(R.id.action_receitaListingFragment_to_receitaDetailFragment,Bundle().apply {

                putParcelable("note",item)
            })
        },
        this.authModel
    )
}

RecipeListingFragment设置Adapter代码 #

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    binding.recyclerView.adapter = adapter
}

navigation.xml代码 #

<navigation 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:id="@+id/app_navigation"
    app:startDestination="@id/receitaListingFragment">

    <fragment
        android:id="@+id/receitaListingFragment"
        android:name="com.example.projectfoodmanager.ui.recipe.RecipeListingFragment"
        android:label="fragment_receita_listing"
        tools:layout="@layout/fragment_recipe_listing" >
        <action
            android:id="@+id/action_receitaListingFragment_to_receitaDetailFragment"
            app:destination="@id/receitaDetailFragment" />
        <action
            android:id="@+id/action_receitaListingFragment_to_profileFragment"
            app:destination="@id/profileFragment" />
    </fragment>

    <fragment
        android:id="@+id/receitaDetailFragment"
        android:name="com.example.projectfoodmanager.ui.recipe.RecipeDetailFragment"
        android:label="fragment_recipe_detail"
        tools:layout="@layout/fragment_recipe_detail" >
        <action
            android:id="@+id/action_receitaDetailFragment_to_receitaListingFragment"
            app:destination="@id/receitaListingFragment" />
    </fragment>
    <fragment
        android:id="@+id/profileFragment"
        android:name="com.example.projectfoodmanager.ui.profile.ProfileFragment"
        android:label="fragment_profile"
        tools:layout="@layout/fragment_profile" >
        <action
            android:id="@+id/action_profileFragment_to_receitaListingFragment"
            app:destination="@id/receitaListingFragment" />
    </fragment>
    <fragment
        android:id="@+id/calenderFragment"
        android:name="com.example.projectfoodmanager.ui.views.CalenderFragment"
        android:label="fragment_calender"
        tools:layout="@layout/fragment_calender" >
    </fragment>
    <fragment
        android:id="@+id/favoritesFragment"
        android:name="com.example.projectfoodmanager.ui.views.FavoritesFragment"
        android:label="fragment_favorites"
        tools:layout="@layout/fragment_favorites" >
    </fragment>
    <fragment
        android:id="@+id/goalFragment"
        android:name="com.example.projectfoodmanager.ui.views.GoalFragment"
        android:label="fragment_goal"
        tools:layout="@layout/fragment_goal" >
    </fragment>

</navigation>

核心问题出在BottomNavigationView的点击事件处理逻辑错误：你没有使用Navigation组件自带的导航能力，而是手动通过replaceFragment替换NavHostFragment容器内的内容，导致：

• 手动替换后，原NavHostFragment被覆盖，Fragment脱离了Navigation的栈管理，返回后无法找到正确的NavController
• Adapter中调用的findNavController()依赖Fragment与NavHost的关联，手动替换破坏了这种关联，返回后触发点击就会抛出找不到NavController的错误

方案1：使用Navigation原生底部导航（推荐） #

完全依托Navigation组件处理底部导航，不需要手动替换Fragment，步骤如下：

1. 移除bottomNav.setOnItemSelectedListener中的手动替换逻辑
2. 确保bottom_nav_menu.xml里的菜单项id，与navigation.xml中对应Fragment的id完全一致
3. 保留bottomNav.setupWithNavController(navController)，让Navigation自动处理导航切换

修改后的MainActivity代码 #

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainMenuBinding
    private lateinit var bottomNav: BottomNavigationView
    private lateinit var navController: NavController
    val authViewModel: AuthViewModel by viewModels()

    val TAG: String = "ReceitaListingFragment"


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        startUI()
    }

    private fun setNavController(){
        val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host) as NavHostFragment
        navController = navHostFragment.navController
        // 让Navigation自动接管底部导航
        bottomNav.setupWithNavController(navController)
    }

    private fun startUI() {
        binding = ActivityMainMenuBinding.inflate(layoutInflater)
        setContentView(binding.root)
        bottomNav = findViewById(R.id.bottomNavigationView)
        setNavController()
        
        // 移除手动替换Fragment的逻辑
    }
}

匹配菜单项与Fragment ID的示例bottom_nav_menu.xml #

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/receitaListingFragment"
        android:icon="@drawable/ic_recipes"
        android:title="Recipes"/>
    <item
        android:id="@+id/profileFragment"
        android:icon="@drawable/ic_profile"
        android:title="Profile"/>
</menu>

方案2：优化Adapter中NavController的获取方式（额外加固） #

在Adapter的点击回调中，通过点击的ItemView来获取NavController，比依赖Fragment更可靠：

修改RecipeListingFragment的Adapter初始化 #

private val adapter by lazy {
    RecipeListingAdapter(
        onItemClicked = { pos, item, view ->
            // 通过点击的View获取NavController
            view.findNavController().navigate(R.id.action_receitaListingFragment_to_receitaDetailFragment, Bundle().apply {
                putParcelable("note", item)
            })
        },
        this.authModel
    )
}

修改Adapter的回调定义 #

class RecipeListingAdapter(
    private val onItemClicked: (Int, Recipe, View) -> Unit,
    private val authModel: AuthViewModel
) : RecyclerView.Adapter<RecipeListingAdapter.ViewHolder>() {
    // ... 其他代码
    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val item = data[position]
        holder.itemView.setOnClickListener {
            // 把点击的View传入回调
            onItemClicked(position, item, it)
        }
    }
}

内容的提问来源于stack exchange，提问作者Rafael Francisco Rodrigues Gar