BottomNavigationView切换Fragment时子Fragment残留问题求助

现有Home、List、Settings三个主Fragment，其中List包含AddFormFragment和EditFormFragment两个子Fragment。使用底部导航切换三个主Fragment时一切正常，但进入List的某个子Fragment后直接切换到其他主Fragment，再切回List时会显示之前的子Fragment，必须点击返回才能回到List主Fragment。需求是切回List时直接显示List主Fragment，而非残留的子Fragment。

导航配置代码（nav_graph.xml） #

<fragment
    android:id="@+id/homeFragment"
    android:name="com.somi.fidelitycardconnect.ui.home.HomeFragment"
    android:label="Home"
    tools:layout="@layout/fragment_home" />

<fragment
    android:id="@+id/settingsFragment"
    android:name="com.somi.fidelitycardconnect.ui.settings.SettingsFragment"
    android:label="Impostazioni"
    tools:layout="@layout/fragment_settings" />

<fragment
    android:id="@+id/listFragment"
    android:name="com.somi.fidelitycardconnect.ui.list.ListFragment"
    android:label="Lista clienti"
    tools:layout="@layout/fragment_list">
    <action
        android:id="@+id/action_listFragment_to_addFormFragment"
        app:destination="@id/addFormFragment" />

    <action
        android:id="@+id/action_listFragment_to_editFormFragment"
        app:destination="@id/editFormFragment" />

</fragment>

<fragment
    android:id="@+id/addFormFragment"
    android:name="com.somi.fidelitycardconnect.ui.form.AddFormFragment"
    android:label="Aggiungi cliente"
    tools:layout="@layout/fragment_add_form">
</fragment>

<fragment
    android:id="@+id/editFormFragment"
    android:name="com.somi.fidelitycardconnect.ui.form.EditFormFragment"
    android:label="Informazioni cliente"
    tools:layout="@layout/fragment_edit_form">
</fragment>

MainActivity代码 #

binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)

val navView: BottomNavigationView = binding.navView

val navController = findNavController(R.id.nav_host_fragment_activity_main)
// Passing each menu ID as a set of Ids because each
// menu should be considered as top level destinations.
appBarConfiguration = AppBarConfiguration(
    setOf(
        R.id.homeFragment,
        R.id.listFragment,
        R.id.settingsFragment
    )
)
setupActionBarWithNavController(navController, appBarConfiguration)
navView.setupWithNavController(navController)
}

override fun onSupportNavigateUp(): Boolean {
    val navController = findNavController(R.id.nav_host_fragment_activity_main)
    return navController.navigateUp(appBarConfiguration)
            || super.onSupportNavigateUp()
}

自定义底部导航点击事件，强制回到List主Fragment #

替换原有的navView.setupWithNavController(navController)，改为自定义选中监听，当点击List项时，判断当前是否处于List的子Fragment，若是则直接回退到List主Fragment，否则正常导航：

binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)

val navView: BottomNavigationView = binding.navView
val navController = findNavController(R.id.nav_host_fragment_activity_main)

appBarConfiguration = AppBarConfiguration(
    setOf(
        R.id.homeFragment,
        R.id.listFragment,
        R.id.settingsFragment
    )
)
setupActionBarWithNavController(navController, appBarConfiguration)

// 自定义底部导航选中逻辑
navView.setOnItemSelectedListener { menuItem ->
    when (menuItem.itemId) {
        R.id.homeFragment -> {
            navController.navigate(R.id.homeFragment)
            true
        }
        R.id.listFragment -> {
            // 若当前不在List主Fragment，直接回退到List主Fragment
            if (navController.currentDestination?.id != R.id.listFragment) {
                navController.popBackStack(R.id.listFragment, false)
            }
            true
        }
        R.id.settingsFragment -> {
            navController.navigate(R.id.settingsFragment)
            true
        }
        else -> false
    }
}

override fun onSupportNavigateUp(): Boolean {
    val navController = findNavController(R.id.nav_host_fragment_activity_main)
    return navController.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
}

补充：优化导航栈的另一种写法 #

如果希望每次点击List项时都完全重置List的导航栈（避免栈中残留任何子Fragment），可以使用navigate方法配合popUpTo参数：

R.id.listFragment -> {
    navController.navigate(R.id.listFragment) {
        // 清空List主Fragment之上的所有栈元素
        popUpTo(R.id.listFragment) {
            inclusive = false
        }
        // 避免重复点击时重复入栈
        launchSingleTop = true
    }
    true
}

内容的提问来源于stack exchange，提问作者Silvano M.