选择底部导航选项卡后Android清除回栈

Question

使用最新的Navigation Component 和BottomNavigationView，NavController 现在默认保存和恢复选项卡的状态：

作为此更改的一部分，onNavDestinationSelected()、BottomNavigationView.setupWithNavController() 和 NavigationView.setupWithNavController() 的 NavigationUI 方法现在可以自动保存和恢复弹出目的地的状态，无需任何代码更改即可支持多个返回堆栈。当使用带有 Fragments 的导航时，这是与多个返回堆栈集成的推荐方式。

这太棒了！现在切换标签会为您提供上次查看的堆栈。

但是，如果用户重新选择一个标签，说他们已经离开Home -> Detail Page A -> Detail Page B，然后他们选择了Home 标签并期望返回到默认视图，他们仍然会看到@987654328 @。

似乎讨论的一部分是处理issue tracker 中提到的“重新选择选项卡”行为，但我想不出推荐的实现方式。

NavigationAdvancedSample 中包含的所有内容是：

val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottom_nav)
bottomNavigationView.setupWithNavController(navController)

// Setup the ActionBar with navController and 3 top level destinations
appBarConfiguration = AppBarConfiguration(
        setOf(R.id.titleScreen, R.id.leaderboard,  R.id.register)
    )
setupActionBarWithNavController(navController, appBarConfiguration)

这只是恢复以前的状态，如发行说明中所述。

我们如何检查第二次点击导航栏项目并清除后台堆栈？

Answer 1

BottomNavigationView 有自己的方法通过setOnItemReselectedListener() 处理重新选择（或者，当使用早期版本的材料设计库时，现在不推荐使用setOnNavigationItemReselectedListener()）。

bottomNavigationView.setupWithNavController 没有设置这个监听器（因为没有关于重新选择选项卡应该做什么的 Material 规范），所以你需要自己设置它：

val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottom_nav)
bottomNavigationView.setupWithNavController(navController)

// Add your own reselected listener
bottomNavigationView.setOnItemReselectedListener { item ->
    // Pop everything up to the reselected item
    val reselectedDestinationId = item.itemId
    navController.popBackStack(reselectedDestinationId, inclusive = false)
}

Answer 2

接受的答案让我朝着正确的方向开始。然而，随着 Android 导航库 2.4.0 支持的多个 backstacks 的添加，这最终对我有用：

val currentRootFragment = supportFragmentManager.findFragmentById(R.id.main_fragment)
val navHost = currentRootFragment as? NavHostFragment
val selectedMenuItemNavGraph = navHost?.navController?.graph?.findNode(menuItem.itemId) as? NavGraph?
selectedMenuItemNavGraph?.let { menuGraph ->
             navHost?.navController?.popBackStack(menuGraph.startDestinationId, false)
}

Answer 3

使用您自己的setupWithNavController2 代替androidx.navigation.ui.BottomNavigationViewKt 中的setupWithNavController

例如：

在导航之前添加了对已选择项目的检查：

   if (navController.popBackStack(item.itemId, false)) {
        return true
    }

见onNavDestinationSelected的cmets，setupWithNavController2的完整代码：

fun BottomNavigationView.setupWithNavController2(navController: NavController) {
    val bottomNavigationView = this
    bottomNavigationView.setOnItemSelectedListener { item ->
        onNavDestinationSelected(item, navController)
    }
    val weakReference = WeakReference(bottomNavigationView)
    navController.addOnDestinationChangedListener(
        object : NavController.OnDestinationChangedListener {
            override fun onDestinationChanged(
                controller: NavController,
                destination: NavDestination,
                arguments: Bundle?
            ) {
                val view = weakReference.get()
                if (view == null) {
                    navController.removeOnDestinationChangedListener(this)
                    return
                }
                val menu = view.menu
                var i = 0
                val size = menu.size()
                while (i < size) {
                    val item = menu.getItem(i)
                    if (matchDestination(destination, item.itemId)) {
                        item.isChecked = true
                    }
                    i++
                }
            }
        })

    // Add your own reselected listener
    bottomNavigationView.setOnItemReselectedListener { item ->
        // Pop everything up to the reselected item
        val reselectedDestinationId = item.itemId
        navController.popBackStack(reselectedDestinationId, false)
    }
}

fun onNavDestinationSelected(
    item: MenuItem,
    navController: NavController
): Boolean {
    val builder = NavOptions.Builder()
        .setLaunchSingleTop(true)
    if (navController.currentDestination?.parent?.findNode(item.itemId) is ActivityNavigator.Destination) {
        builder.setEnterAnim(R.anim.nav_default_enter_anim)
            .setExitAnim(R.anim.nav_default_exit_anim)
            .setPopEnterAnim(R.anim.nav_default_pop_enter_anim)
            .setPopExitAnim(R.anim.nav_default_pop_exit_anim)
    } else {
        builder.setEnterAnim(R.animator.nav_default_enter_anim)
            .setExitAnim(R.animator.nav_default_exit_anim)
            .setPopEnterAnim(R.animator.nav_default_pop_enter_anim)
            .setPopExitAnim(R.animator.nav_default_pop_exit_anim)
    }
    if (item.order and Menu.CATEGORY_SECONDARY == 0) {
        val findStartDestination = findStartDestination(navController.graph)
        if (findStartDestination != null) {
            builder.setPopUpTo(findStartDestination.id, false)
        }
    }
    val options = builder.build()
    //region The code was added to avoid adding already exist item
    if (navController.popBackStack(item.itemId, false)) {
        return true
    }
    //endregion
    return try {
        // TODO provide proper API instead of using Exceptions as Control-Flow.
        navController.navigate(item.itemId, null, options)
        true
    } catch (e: IllegalArgumentException) {
        false
    }
}

fun findStartDestination(graph: NavGraph): NavDestination? {
    var startDestination: NavDestination? = graph
    while (startDestination is NavGraph) {
        val parent = startDestination
        startDestination = parent.findNode(parent.startDestination)
    }
    return startDestination
}

fun matchDestination(
    destination: NavDestination,
    @IdRes destId: Int
): Boolean {
    var currentDestination: NavDestination? = destination
    while (currentDestination?.id != destId && currentDestination?.parent != null) {
        currentDestination = currentDestination.parent
    }
    return currentDestination?.id == destId
}

Answer 4

这里有两种方法可以解决...

1. 在选择项目后更新选择（带有后退堆栈的项目，最新版本 - 2.4.2，当顶部目的地存在后退堆栈时，选择该项目不会首先选择项目）。

   NavigationBarView.setOnItemSelectedListener {}

2. 等待第二次点击并弹出回栈。

   NavigationBarView.setOnItemReselectedListener {}

最终代码是，

val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment?
    val navController = navHostFragment?.navController

    mainBinding?.bottomNavigation?.apply {
        navController?.let { navController ->
            NavigationUI.setupWithNavController(
                this,
                navController
            )
            setOnItemSelectedListener { item ->
                NavigationUI.onNavDestinationSelected(item, navController)
                true
            }
            setOnItemReselectedListener {
                navController.popBackStack(destinationId = it.itemId, inclusive = false)
            }
        }

}

希望这会有所帮助..