Android Jetpack Navigation、BottomNavigationView 与 Youtube 或 Instagram 类似的正确后退导航（片段后退堆栈）？
Android Jetpack Navigation, BottomNavigationView with Youtube or Instagram like proper back navigation (fragment back stack)?
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android
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android-architecture-components
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bottomnavigationview
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android-navigation
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android-architecture-navigation
Android Jetpack Navigation，BottomNavigationView 在后退按钮点击时带有自动片段返回堆栈？
我想要的是，在用户一个接一个地选择多个选项卡后，用户点击后退按钮应用程序必须重定向到最后打开的页面 he/she。
我使用 Android ViewPager 实现了同样的效果，方法是将当前选定的项目保存在 ArrayList 中。 Android Jetpack Navigation Release 后是否有任何自动返回堆栈？我想用导航图来实现
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".main.MainActivity">
<fragment
android:id="@+id/my_nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="0dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="@+id/navigation"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="@navigation/nav_graph" />
<android.support.design.widget.BottomNavigationView
android:id="@+id/navigation"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:menu="@menu/navigation" />
</android.support.constraint.ConstraintLayout>
navigation.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@+id/navigation_home"
android:icon="@drawable/ic_home"
android:title="@string/title_home" />
<item
android:id="@+id/navigation_people"
android:icon="@drawable/ic_group"
android:title="@string/title_people" />
<item
android:id="@+id/navigation_organization"
android:icon="@drawable/ic_organization"
android:title="@string/title_organization" />
<item
android:id="@+id/navigation_business"
android:icon="@drawable/ic_business"
android:title="@string/title_business" />
<item
android:id="@+id/navigation_tasks"
android:icon="@drawable/ic_dashboard"
android:title="@string/title_tasks" />
</menu>
还添加了
bottomNavigation.setupWithNavController(Navigation.findNavController(this, R.id.my_nav_host_fragment))
我从Levi Moreira那里得到了一个答案，如下
navigation.setOnNavigationItemSelectedListener {item ->
onNavDestinationSelected(item, Navigation.findNavController(this, R.id.my_nav_host_fragment))
}
但是这样做只会发生最后打开的片段的实例再次创建。
为 BottomNavigationView 提供适当的返回导航
您可以设置带有底部导航视图的 viewpager。 viewpager 中的每个片段都是一个容器片段，它将有带有自己的后台堆栈的子片段。您可以通过这种方式为 viewpager 中的每个选项卡维护 backstack
您并不需要 ViewPager 来使用 BottomNavigation 和新的导航架构组件。我一直在开发一个完全使用这两者的示例应用程序，请参阅 here。
基本概念是这样的，您有主要的 activity 将托管 BottomNavigationView，这是导航图的导航主机，这就是 xml 的方式它看起来像：
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".main.MainActivity">
<fragment
android:id="@+id/my_nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="0dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="@+id/navigation"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="@navigation/nav_graph" />
<android.support.design.widget.BottomNavigationView
android:id="@+id/navigation"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:menu="@menu/navigation" />
</android.support.constraint.ConstraintLayout>
BottomNavigationView 的导航菜单（选项卡菜单）如下所示：
navigation.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@+id/navigation_home"
android:icon="@drawable/ic_home"
android:title="@string/title_home" />
<item
android:id="@+id/navigation_people"
android:icon="@drawable/ic_group"
android:title="@string/title_people" />
<item
android:id="@+id/navigation_organization"
android:icon="@drawable/ic_organization"
android:title="@string/title_organization" />
<item
android:id="@+id/navigation_business"
android:icon="@drawable/ic_business"
android:title="@string/title_business" />
<item
android:id="@+id/navigation_tasks"
android:icon="@drawable/ic_dashboard"
android:title="@string/title_tasks" />
</menu>
所有这些只是 BottomNavigationView 设置。现在要使其与 Navigation Arch Component 一起工作，您需要进入导航图编辑器，添加所有片段目的地（在我的例子中，我有 5 个，每个选项卡一个）并使用相同的设置目的地的 id navigation.xml 文件中的名称：
这将告诉 android 在选项卡和片段之间创建一个 link，现在每次用户单击 "Home" 选项卡时 android 都会处理加载正确的片段。
还需要将一段 kotlin 代码添加到您的 NavHost（主要 activity），以将内容与 BottomNavigationView:
连接起来
你需要在你的onCreate中添加：
bottomNavigation.setupWithNavController(Navigation.findNavController(this, R.id.my_nav_host_fragment))
这告诉 android 在导航架构组件和 BottomNavigationView 之间进行连接。在 docs.
中查看更多信息
要获得与使用 youtube 时相同的行为，只需添加：
navigation.setOnNavigationItemSelectedListener {item ->
onNavDestinationSelected(item, Navigation.findNavController(this, R.id.my_nav_host_fragment))
}
这将使目的地进入后退堆栈，因此当您点击后退按钮时，将弹出上次访问的目的地。
我制作了一个类似这样的应用程序（仍未在 PlayStore 上发布），它具有相同的导航功能，也许它的实现与 Google 在他们的应用程序中所做的不同，但功能是相同的。
结构涉及我有 Main Activity，我使用 showing/hiding 片段切换它的内容：
public void switchTo(final Fragment fragment, final String tag /*Each fragment should have a different Tag*/) {
// We compare if the current stack is the current fragment we try to show
if (fragment == getSupportFragmentManager().getPrimaryNavigationFragment()) {
return;
}
// We need to hide the current showing fragment (primary fragment)
final Fragment currentShowingFragment = getSupportFragmentManager().getPrimaryNavigationFragment();
final FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
if (currentShowingFragment != null) {
fragmentTransaction.hide(currentShowingFragment);
}
// We try to find that fragment if it was already added before
final Fragment alreadyAddedFragment = getSupportFragmentManager().findFragmentByTag(tag);
if (alreadyAddedFragment != null) {
// Since its already added before we just set it as primary navigation and show it again
fragmentTransaction.setPrimaryNavigationFragment(alreadyAddedFragment);
fragmentTransaction.show(alreadyAddedFragment);
} else {
// We add the new fragment and then show it
fragmentTransaction.add(containerId, fragment, tag);
fragmentTransaction.show(fragment);
// We set it as the primary navigation to support back stack and back navigation
fragmentTransaction.setPrimaryNavigationFragment(fragment);
}
fragmentTransaction.commit();
}
您必须像下面这样设置主机导航xml:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/colorPrimary" />
<fragment
android:id="@+id/navigation_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
app:defaultNavHost="true"
app:navGraph="@navigation/nav_graph" />
<android.support.design.widget.BottomNavigationView
android:id="@+id/bottom_navigation_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:itemIconTint="@drawable/color_state_list"
app:itemTextColor="@drawable/color_state_list"
app:menu="@menu/menu_bottom_navigation" />
</LinearLayout>
设置导航控制器：
NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.navigation_host_fragment);
NavigationUI.setupWithNavController(bottomNavigationView, navHostFragment.getNavController());
menu_bottom_navigation.xml :
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@id/tab1" // Id of navigation graph
android:icon="@mipmap/ic_launcher"
android:title="@string/tab1" />
<item
android:id="@id/tab2" // Id of navigation graph
android:icon="@mipmap/ic_launcher"
android:title="@string/tab2" />
<item
android:id="@id/tab3" // Id of navigation graph
android:icon="@mipmap/ic_launcher"
android:title="@string/tab3" />
</menu>
nav_graph.xml :
<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/nav_graph"
app:startDestination="@id/tab1">
<fragment
android:id="@+id/tab1"
android:name="com.navigationsample.Tab1Fragment"
android:label="@string/tab1"
tools:layout="@layout/fragment_tab_1" />
<fragment
android:id="@+id/tab2"
android:name="com.navigationsample.Tab2Fragment"
android:label="@string/tab2"
tools:layout="@layout/fragment_tab_2"/>
<fragment
android:id="@+id/tab3"
android:name="com.simform.navigationsample.Tab3Fragment"
android:label="@string/tab3"
tools:layout="@layout/fragment_tab_3"/>
</navigation>
通过设置与"nav_graph"相同的id到"menu_bottom_navigation"将处理底部导航的点击。
您可以在 action 标签中使用 popUpTo 属性 处理返回操作。
如果您有一个 bottomNavigationView，其中 3 个项目对应 3 个 Fragment：FragmentA、FragmentB 和 FragmentC，其中 FragmentA是导航图中的 startDestination，然后当您在 FragmentB 或 FragmentC 上并单击后退时，您将被重定向到 FragmentA，这就是Google 推荐的行为，默认情况下实现。
但是，如果您希望改变此行为，则需要按照其他一些答案的建议使用 ViewPager，或者您自己手动处理片段 backStack 和返回事务 - 这在一种方法会完全破坏导航组件的使用-。
首先，让我澄清一下 Youtube 和 Instagram 是如何处理片段导航的。
- 当用户位于详细信息片段上时，向后或向上弹出堆栈一次，并正确恢复状态。第二次点击已经选择的底部栏项目弹出所有堆栈到根，刷新它
- 当用户在根片段上时，返回到底部栏上最后选择的菜单，显示最后一个细节片段，状态正确恢复（JetPack 没有）
- 当用户在起始目标片段上时，返回完成 activity
None 以上其他答案使用喷气背包导航解决了所有这些问题。
JetPack 导航没有标准的方法来做到这一点，我发现更简单的方法是将导航 xml 图分成每个底部导航项，自己处理导航项之间的返回堆栈使用 activity FragmentManager 并使用 JetPack NavController 处理根片段和细节片段之间的内部导航（其实现使用 childFragmentManager 堆栈）。
假设您的 navigation 文件夹中有这 3 xmls:
res/navigation/
navigation_feed.xml
navigation_explore.xml
navigation_profile.xml
导航中的 destinationIds xml与 bottomNavigationBar 菜单 ids 相同。此外，对于每个 xml 将 app:startDestination 设置为您想要作为导航项根的片段。
创建 class BottomNavController.kt:
class BottomNavController(
val context: Context,
@IdRes val containerId: Int,
@IdRes val appStartDestinationId: Int
) {
private val navigationBackStack = BackStack.of(appStartDestinationId)
lateinit var activity: Activity
lateinit var fragmentManager: FragmentManager
private var listener: OnNavigationItemChanged? = null
private var navGraphProvider: NavGraphProvider? = null
interface OnNavigationItemChanged {
fun onItemChanged(itemId: Int)
}
interface NavGraphProvider {
@NavigationRes
fun getNavGraphId(itemId: Int): Int
}
init {
var ctx = context
while (ctx is ContextWrapper) {
if (ctx is Activity) {
activity = ctx
fragmentManager = (activity as FragmentActivity).supportFragmentManager
break
}
ctx = ctx.baseContext
}
}
fun setOnItemNavigationChanged(listener: (itemId: Int) -> Unit) {
this.listener = object : OnNavigationItemChanged {
override fun onItemChanged(itemId: Int) {
listener.invoke(itemId)
}
}
}
fun setNavGraphProvider(provider: NavGraphProvider) {
navGraphProvider = provider
}
fun onNavigationItemReselected(item: MenuItem) {
// If the user press a second time the navigation button, we pop the back stack to the root
activity.findNavController(containerId).popBackStack(item.itemId, false)
}
fun onNavigationItemSelected(itemId: Int = navigationBackStack.last()): Boolean {
// Replace fragment representing a navigation item
val fragment = fragmentManager.findFragmentByTag(itemId.toString())
?: NavHostFragment.create(navGraphProvider?.getNavGraphId(itemId)
?: throw RuntimeException("You need to set up a NavGraphProvider with " +
"BottomNavController#setNavGraphProvider")
)
fragmentManager.beginTransaction()
.setCustomAnimations(
R.anim.nav_default_enter_anim,
R.anim.nav_default_exit_anim,
R.anim.nav_default_pop_enter_anim,
R.anim.nav_default_pop_exit_anim
)
.replace(containerId, fragment, itemId.toString())
.addToBackStack(null)
.commit()
// Add to back stack
navigationBackStack.moveLast(itemId)
listener?.onItemChanged(itemId)
return true
}
fun onBackPressed() {
val childFragmentManager = fragmentManager.findFragmentById(containerId)!!
.childFragmentManager
when {
// We should always try to go back on the child fragment manager stack before going to
// the navigation stack. It's important to use the child fragment manager instead of the
// NavController because if the user change tabs super fast commit of the
// supportFragmentManager may mess up with the NavController child fragment manager back
// stack
childFragmentManager.popBackStackImmediate() -> {
}
// Fragment back stack is empty so try to go back on the navigation stack
navigationBackStack.size > 1 -> {
// Remove last item from back stack
navigationBackStack.removeLast()
// Update the container with new fragment
onNavigationItemSelected()
}
// If the stack has only one and it's not the navigation home we should
// ensure that the application always leave from startDestination
navigationBackStack.last() != appStartDestinationId -> {
navigationBackStack.removeLast()
navigationBackStack.add(0, appStartDestinationId)
onNavigationItemSelected()
}
// Navigation stack is empty, so finish the activity
else -> activity.finish()
}
}
private class BackStack : ArrayList<Int>() {
companion object {
fun of(vararg elements: Int): BackStack {
val b = BackStack()
b.addAll(elements.toTypedArray())
return b
}
}
fun removeLast() = removeAt(size - 1)
fun moveLast(item: Int) {
remove(item)
add(item)
}
}
}
// Convenience extension to set up the navigation
fun BottomNavigationView.setUpNavigation(bottomNavController: BottomNavController, onReselect: ((menuItem: MenuItem) -> Unit)? = null) {
setOnNavigationItemSelectedListener {
bottomNavController.onNavigationItemSelected(it.itemId)
}
setOnNavigationItemReselectedListener {
bottomNavController.onNavigationItemReselected(it)
onReselect?.invoke(it)
}
bottomNavController.setOnItemNavigationChanged { itemId ->
menu.findItem(itemId).isChecked = true
}
}
这样布局 main.xml：
<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">
<FrameLayout
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="0dp"
app:layout_constraintBottom_toTopOf="@id/bottomNavigationView"
app:layout_constraintTop_toTopOf="parent" />
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/bottomNavigationView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
app:layout_constraintBottom_toBottomOf="parent"
app:menu="@menu/navigation" />
</androidx.constraintlayout.widget.ConstraintLayout>
像这样在 activity 上使用：
class MainActivity : AppCompatActivity(),
BottomNavController.NavGraphProvider {
private val navController by lazy(LazyThreadSafetyMode.NONE) {
Navigation.findNavController(this, R.id.container)
}
private val bottomNavController by lazy(LazyThreadSafetyMode.NONE) {
BottomNavController(this, R.id.container, R.id.navigation_feed)
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.main)
bottomNavController.setNavGraphProvider(this)
bottomNavigationView.setUpNavigation(bottomNavController)
if (savedInstanceState == null) bottomNavController
.onNavigationItemSelected()
// do your things...
}
override fun getNavGraphId(itemId: Int) = when (itemId) {
R.id.navigation_feed -> R.navigation.navigation_feed
R.id.navigation_explore -> R.navigation.navigation_explore
R.id.navigation_profile -> R.navigation.navigation_profile
else -> R.navigation.navigation_feed
}
override fun onSupportNavigateUp(): Boolean = navController
.navigateUp()
override fun onBackPressed() = bottomNavController.onBackPressed()
}
Kotlin 中用于将底部导航项与导航图中的片段连接起来的短而好的代码：
val navControl = findNavController( R.id.nav_host_frag_main)
bottomNavigationView?.setupWithNavController(navControl)
*只是 consider:Bottom 导航图中的导航 ID 和片段必须具有相同的 ID。
还要感谢@sanat Answer
的良好解释
最好的解决方案是由 google 团队在他的回购协议中提供的解决方案，后退按钮仍会将您送回第一个按钮，但其余行为是 "normal"... 看起来不幸的是 Google 仍然没有提供好的解决方案，即使他们在（youtube、Google 照片等）上使用它，他们说 androidx 可以提供帮助，但看起来就像我们四处寻找正常的解决方法。
这是他们使用导航的 link 到 google 回购。底部每个按钮都有一个 navGraph。
https://github.com/android/architecture-components-samples/blob/master/NavigationAdvancedSample/app/src/main/java/com/example/android/navigationadvancedsample/NavigationExtensions.kt 将这个文件复制到你的项目中，看看它是如何在他们的项目中实现的。对于后退按钮行为，您可以创建自己的堆栈，onBackpressed 只需在该堆栈上导航。
我没有找到任何官方解决方案，但我用自己的方式
首先，我为句柄片段创建 Stack
needToAddToBackStack : Boolen = true
private lateinit var fragmentBackStack: Stack<Int>
fragmentBackStack = Stack()
并在
navController.addOnDestinationChangedListener { _, destination, _ ->
if (needToAddToBackStack) {
fragmentBackStack.add(destination.id)
}
needToAddToBackStack = true
}
并处理后退按钮
override fun onBackPressed() {
if (::fragmentBackStack.isInitialized && fragmentBackStack.size > 1) {
fragmentBackStack.pop()
val fragmentId = fragmentBackStack.lastElement()
needToAddToBackStack = false
navController.navigate(fragmentId)
} else {
if (::fragmentBackStack.isInitialized && fragmentBackStack.size == 1) {
finish()
} else {
super.onBackPressed()
}
}
看完你的问题后，我再次检查了Google文档。我看到他们提供了一个解决方案，使 Navigation UI 与 BottomNavigationView 一起工作。所以，我为任何像我一样需要它的人创建了一个教程。
对于文本版本：https://nhatvm.com/how-to-use-navigationui-with-bottomnavigation-in-android/
对于 youtube 版本：https://youtu.be/2uxILvBbkyY
在 Jetpack 导航中，您必须仅在单个导航图 xml 文件中进行更改以处理导航、处理后台堆栈、自定义动画、在片段之间传递参数。
如果您只想回到上一个片段，
<action
android:id="@+id/action_deleteEmployeeFragment_to_employeesListFragment2"
app:destination="@id/employeesListFragment"/>
btn_cancel.setOnClickListener {
it.findNavController().popBackStack()
}
如果你想清除所有的backstack并转到新的片段
<action
android:id="@+id/action_deleteEmployeeFragment_to_employeesListFragment2"
app:destination="@id/employeesListFragment"
app:popUpTo="@id/employeesListFragment"
app:popUpToInclusive="true"
app:launchSingleTop="true" />
btn_submit.setOnClickListener {
it.findNavController().navigate(DeleteEmployeeFragmentDirections.actionDeleteEmployeeFragmentToEmployeesListFragment2())
}
拥有一个适当的后栈来保持状态的关键是 NavHostFragment 有 childFragmentManager 和它们自己的后栈。 Navigation组件高级示例的扩展文件就是这样做的
/**
* Manages the various graphs needed for a [BottomNavigationView].
*
* This sample is a workaround until the Navigation Component supports multiple back stacks.
*/
fun BottomNavigationView.setupWithNavController(
navGraphIds: List<Int>,
fragmentManager: FragmentManager,
containerId: Int,
intent: Intent
): LiveData<NavController> {
// Map of tags
val graphIdToTagMap = SparseArray<String>()
// Result. Mutable live data with the selected controlled
val selectedNavController = MutableLiveData<NavController>()
var firstFragmentGraphId = 0
// First create a NavHostFragment for each NavGraph ID
navGraphIds.forEachIndexed { index, navGraphId ->
val fragmentTag = getFragmentTag(index)
// Find or create the Navigation host fragment
val navHostFragment = obtainNavHostFragment(
fragmentManager,
fragmentTag,
navGraphId,
containerId
)
// Obtain its id
val graphId = navHostFragment.navController.graph.id
if (index == 0) {
firstFragmentGraphId = graphId
}
// Save to the map
graphIdToTagMap[graphId] = fragmentTag
// Attach or detach nav host fragment depending on whether it's the selected item.
if (this.selectedItemId == graphId) {
// Update livedata with the selected graph
selectedNavController.value = navHostFragment.navController
attachNavHostFragment(fragmentManager, navHostFragment, index == 0)
} else {
detachNavHostFragment(fragmentManager, navHostFragment)
}
}
// Now connect selecting an item with swapping Fragments
var selectedItemTag = graphIdToTagMap[this.selectedItemId]
val firstFragmentTag = graphIdToTagMap[firstFragmentGraphId]
var isOnFirstFragment = selectedItemTag == firstFragmentTag
// When a navigation item is selected
setOnNavigationItemSelectedListener { item ->
// Don't do anything if the state is state has already been saved.
if (fragmentManager.isStateSaved) {
false
} else {
val newlySelectedItemTag = graphIdToTagMap[item.itemId]
if (selectedItemTag != newlySelectedItemTag) {
// Pop everything above the first fragment (the "fixed start destination")
fragmentManager.popBackStack(
firstFragmentTag,
FragmentManager.POP_BACK_STACK_INCLUSIVE
)
val selectedFragment = fragmentManager.findFragmentByTag(newlySelectedItemTag)
as NavHostFragment
// Exclude the first fragment tag because it's always in the back stack.
if (firstFragmentTag != newlySelectedItemTag) {
// Commit a transaction that cleans the back stack and adds the first fragment
// to it, creating the fixed started destination.
fragmentManager.beginTransaction()
.attach(selectedFragment)
.setPrimaryNavigationFragment(selectedFragment)
.apply {
// Detach all other Fragments
graphIdToTagMap.forEach { _, fragmentTagIter ->
if (fragmentTagIter != newlySelectedItemTag) {
detach(fragmentManager.findFragmentByTag(firstFragmentTag)!!)
}
}
}
.addToBackStack(firstFragmentTag)
.setCustomAnimations(
R.anim.nav_default_enter_anim,
R.anim.nav_default_exit_anim,
R.anim.nav_default_pop_enter_anim,
R.anim.nav_default_pop_exit_anim
)
.setReorderingAllowed(true)
.commit()
}
selectedItemTag = newlySelectedItemTag
isOnFirstFragment = selectedItemTag == firstFragmentTag
selectedNavController.value = selectedFragment.navController
true
} else {
false
}
}
}
// Optional: on item reselected, pop back stack to the destination of the graph
setupItemReselected(graphIdToTagMap, fragmentManager)
// Handle deep link
setupDeepLinks(navGraphIds, fragmentManager, containerId, intent)
// Finally, ensure that we update our BottomNavigationView when the back stack changes
fragmentManager.addOnBackStackChangedListener {
if (!isOnFirstFragment && !fragmentManager.isOnBackStack(firstFragmentTag)) {
this.selectedItemId = firstFragmentGraphId
}
// Reset the graph if the currentDestination is not valid (happens when the back
// stack is popped after using the back button).
selectedNavController.value?.let { controller ->
if (controller.currentDestination == null) {
controller.navigate(controller.graph.id)
}
}
}
return selectedNavController
}
private fun BottomNavigationView.setupDeepLinks(
navGraphIds: List<Int>,
fragmentManager: FragmentManager,
containerId: Int,
intent: Intent
) {
navGraphIds.forEachIndexed { index, navGraphId ->
val fragmentTag = getFragmentTag(index)
// Find or create the Navigation host fragment
val navHostFragment = obtainNavHostFragment(
fragmentManager,
fragmentTag,
navGraphId,
containerId
)
// Handle Intent
if (navHostFragment.navController.handleDeepLink(intent)
&& selectedItemId != navHostFragment.navController.graph.id
) {
this.selectedItemId = navHostFragment.navController.graph.id
}
}
}
private fun BottomNavigationView.setupItemReselected(
graphIdToTagMap: SparseArray<String>,
fragmentManager: FragmentManager
) {
setOnNavigationItemReselectedListener { item ->
val newlySelectedItemTag = graphIdToTagMap[item.itemId]
val selectedFragment = fragmentManager.findFragmentByTag(newlySelectedItemTag)
as NavHostFragment
val navController = selectedFragment.navController
// Pop the back stack to the start destination of the current navController graph
navController.popBackStack(
navController.graph.startDestination, false
)
}
}
private fun detachNavHostFragment(
fragmentManager: FragmentManager,
navHostFragment: NavHostFragment
) {
fragmentManager.beginTransaction()
.detach(navHostFragment)
.commitNow()
}
private fun attachNavHostFragment(
fragmentManager: FragmentManager,
navHostFragment: NavHostFragment,
isPrimaryNavFragment: Boolean
) {
fragmentManager.beginTransaction()
.attach(navHostFragment)
.apply {
if (isPrimaryNavFragment) {
setPrimaryNavigationFragment(navHostFragment)
}
}
.commitNow()
}
private fun obtainNavHostFragment(
fragmentManager: FragmentManager,
fragmentTag: String,
navGraphId: Int,
containerId: Int
): NavHostFragment {
// If the Nav Host fragment exists, return it
val existingFragment = fragmentManager.findFragmentByTag(fragmentTag) as NavHostFragment?
existingFragment?.let { return it }
// Otherwise, create it and return it.
val navHostFragment = NavHostFragment.create(navGraphId)
fragmentManager.beginTransaction()
.add(containerId, navHostFragment, fragmentTag)
.commitNow()
return navHostFragment
}
private fun FragmentManager.isOnBackStack(backStackName: String): Boolean {
val backStackCount = backStackEntryCount
for (index in 0 until backStackCount) {
if (getBackStackEntryAt(index).name == backStackName) {
return true
}
}
return false
}
private fun getFragmentTag(index: Int) = "bottomNavigation#$index"
这里重要的部分是如果NavHostFragment不存在于返回堆栈中，则使用上述函数将其添加到返回堆栈中。 commitNow 是同步的，不像 commit
私享乐趣obtainNavHostFragment(
片段管理器：片段管理器，
片段标签：字符串，
navGraphId：整数，
containerId: Int
): NavHostFragment {
// 如果 Nav Host 片段存在，return 它
val existingFragment = fragmentManager.findFragmentByTag(fragmentTag) 作为 NavHostFragment？
existingFragment?.let { return 它 }
// Otherwise, create it and return it.
val navHostFragment = NavHostFragment.create(navGraphId)
fragmentManager.beginTransaction()
.add(containerId, navHostFragment, fragmentTag)
.commitNow()
return navHostFragment
}
我使用上面的 NavigationExtension 构建了一个，看起来像这样
嵌套导航。
导航图都差不多，我只加一个
nav_graph_home.xml
<?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"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/nav_graph_home"
app:startDestination="@id/homeFragment1">
<fragment
android:id="@+id/homeFragment1"
android:name="com.smarttoolfactory.tutorial5_3navigationui_bottomnavigation_nestednavigation.blankfragment.HomeFragment1"
android:label="HomeFragment1"
tools:layout="@layout/fragment_home1">
<action
android:id="@+id/action_homeFragment1_to_homeFragment2"
app:destination="@id/homeFragment2" />
</fragment>
<fragment
android:id="@+id/homeFragment2"
android:name="com.smarttoolfactory.tutorial5_3navigationui_bottomnavigation_nestednavigation.blankfragment.HomeFragment2"
android:label="HomeFragment2"
tools:layout="@layout/fragment_home2">
<action
android:id="@+id/action_homeFragment2_to_homeFragment3"
app:destination="@id/homeFragment3" />
</fragment>
<fragment
android:id="@+id/homeFragment3"
android:name="com.smarttoolfactory.tutorial5_3navigationui_bottomnavigation_nestednavigation.blankfragment.HomeFragment3"
android:label="HomeFragment3"
tools:layout="@layout/fragment_home3" >
<action
android:id="@+id/action_homeFragment3_to_homeFragment1"
app:destination="@id/homeFragment1"
app:popUpTo="@id/homeFragment1"
app:popUpToInclusive="true" />
</fragment>
</navigation>
底部导航菜单
menu_bottom_nav.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@+id/nav_graph_home"
android:icon="@drawable/ic_baseline_home_24"
android:title="Home"/>
<item
android:id="@+id/nav_graph_dashboard"
android:icon="@drawable/ic_baseline_dashboard_24"
android:title="Dashboard"/>
<item
android:id="@+id/nav_graph_notification"
android:icon="@drawable/ic_baseline_notifications_24"
android:title="Notification"/>
</menu>
包含 FragmentContainerView 和 BottomNavigationView
的 MainActivity 布局
activiy_main.xml
<?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_container"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintBottom_toTopOf="@+id/bottom_nav"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/bottom_nav"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:menu="@menu/menu_bottom_nav" />
</androidx.constraintlayout.widget.ConstraintLayout>
MainActivity.kt
class MainActivity : AppCompatActivity() {
private var currentNavController: LiveData<NavController>? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
supportFragmentManager.addOnBackStackChangedListener {
val backStackEntryCount = supportFragmentManager.backStackEntryCount
val fragments = supportFragmentManager.fragments
val fragmentCount = fragments.size
Toast.makeText(
this,
"MainActivity backStackEntryCount: $backStackEntryCount, fragmentCount: $fragmentCount, fragments: $fragments",
Toast.LENGTH_SHORT
).show()
}
if (savedInstanceState == null) {
setupBottomNavigationBar()
} // Else, need to wait for onRestoreInstanceState
}
override fun onRestoreInstanceState(savedInstanceState: Bundle?) {
super.onRestoreInstanceState(savedInstanceState)
// Now that BottomNavigationBar has restored its instance state
// and its selectedItemId, we can proceed with setting up the
// BottomNavigationBar with Navigation
setupBottomNavigationBar()
}
/**
* Called on first creation and when restoring state.
*/
private fun setupBottomNavigationBar() {
val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottom_nav)
val navGraphIds = listOf(
R.navigation.nav_graph_home,
R.navigation.nav_graph_dashboard,
R.navigation.nav_graph_notification
)
// Setup the bottom navigation view with a list of navigation graphs
val controller = bottomNavigationView.setupWithNavController(
navGraphIds = navGraphIds,
fragmentManager = supportFragmentManager,
containerId = R.id.nav_host_container,
intent = intent
)
// Whenever the selected controller changes, setup the action bar.
controller.observe(this, Observer { navController ->
setupActionBarWithNavController(navController)
})
currentNavController = controller
}
override fun onSupportNavigateUp(): Boolean {
return currentNavController?.value?.navigateUp() ?: false
}
}
片段布局和 类 很简单 类 所以我跳过了它们 out.You 可以查看 full sample i built, or Google's repository 以检查高级导航或其他示例的扩展。
最初在这里回答：
在Jetpack Navigation Componenet中，如果你想在fragment弹出时执行一些操作，那么你需要覆盖以下函数。
将片段中的 OnBackPressedCallback 添加到 运行 按下后退时的特殊操作出现在底部的系统导航栏中。
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
onBackPressedCallback = object : OnBackPressedCallback(true) {
override fun handleOnBackPressed() {
//perform your operation and call navigateUp
findNavController().navigateUp()
}
}
requireActivity().onBackPressedDispatcher.addCallback(onBackPressedCallback)
}
在片段中添加 onOptionsItemMenu 以处理应用内左上角的后退箭头按下。
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
setHasOptionsMenu(true)
}
override fun onOptionsItemSelected(item: MenuItem): Boolean {
if (item.itemId == android.R.id.home) {
//perform your operation and call navigateUp
findNavController().navigateUp()
return true
}
return super.onOptionsItemSelected(item)
}
如果在主机片段上按下后退时没有特殊代码 运行 则在 Activity.
中使用 onSupportNavigateUp
override fun onSupportNavigateUp(): Boolean {
if (navController.navigateUp() == false){
//navigateUp() returns false if there are no more fragments to pop
onBackPressed()
}
return navController.navigateUp()
}
请注意，如果片段包含 onOptionsItemSelected()
，则不会调用 onSupportNavigateUp()
随着2.4.0版本的导航包，终于正式支持了！
https://developer.android.com/jetpack/androidx/releases/navigation#version_240_2
不仅如此：将导航库上传到此版本后，此功能是默认行为。作为旁注，现在此默认行为包括在片段之间导航时不会重新创建片段，。
android
android-architecture-components
bottomnavigationview
android-navigation
android-architecture-navigation
Android Jetpack Navigation，BottomNavigationView 在后退按钮点击时带有自动片段返回堆栈？
我想要的是，在用户一个接一个地选择多个选项卡后，用户点击后退按钮应用程序必须重定向到最后打开的页面 he/she。
我使用 Android ViewPager 实现了同样的效果，方法是将当前选定的项目保存在 ArrayList 中。 Android Jetpack Navigation Release 后是否有任何自动返回堆栈？我想用导航图来实现
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".main.MainActivity">
<fragment
android:id="@+id/my_nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="0dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="@+id/navigation"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="@navigation/nav_graph" />
<android.support.design.widget.BottomNavigationView
android:id="@+id/navigation"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:menu="@menu/navigation" />
</android.support.constraint.ConstraintLayout>
navigation.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@+id/navigation_home"
android:icon="@drawable/ic_home"
android:title="@string/title_home" />
<item
android:id="@+id/navigation_people"
android:icon="@drawable/ic_group"
android:title="@string/title_people" />
<item
android:id="@+id/navigation_organization"
android:icon="@drawable/ic_organization"
android:title="@string/title_organization" />
<item
android:id="@+id/navigation_business"
android:icon="@drawable/ic_business"
android:title="@string/title_business" />
<item
android:id="@+id/navigation_tasks"
android:icon="@drawable/ic_dashboard"
android:title="@string/title_tasks" />
</menu>
还添加了
bottomNavigation.setupWithNavController(Navigation.findNavController(this, R.id.my_nav_host_fragment))
我从Levi Moreira那里得到了一个答案，如下
navigation.setOnNavigationItemSelectedListener {item ->
onNavDestinationSelected(item, Navigation.findNavController(this, R.id.my_nav_host_fragment))
}
但是这样做只会发生最后打开的片段的实例再次创建。
为 BottomNavigationView 提供适当的返回导航
您可以设置带有底部导航视图的 viewpager。 viewpager 中的每个片段都是一个容器片段，它将有带有自己的后台堆栈的子片段。您可以通过这种方式为 viewpager 中的每个选项卡维护 backstack
您并不需要 ViewPager 来使用 BottomNavigation 和新的导航架构组件。我一直在开发一个完全使用这两者的示例应用程序，请参阅 here。
基本概念是这样的，您有主要的 activity 将托管 BottomNavigationView，这是导航图的导航主机，这就是 xml 的方式它看起来像：
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".main.MainActivity">
<fragment
android:id="@+id/my_nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="0dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="@+id/navigation"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="@navigation/nav_graph" />
<android.support.design.widget.BottomNavigationView
android:id="@+id/navigation"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:menu="@menu/navigation" />
</android.support.constraint.ConstraintLayout>
BottomNavigationView 的导航菜单（选项卡菜单）如下所示：
navigation.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@+id/navigation_home"
android:icon="@drawable/ic_home"
android:title="@string/title_home" />
<item
android:id="@+id/navigation_people"
android:icon="@drawable/ic_group"
android:title="@string/title_people" />
<item
android:id="@+id/navigation_organization"
android:icon="@drawable/ic_organization"
android:title="@string/title_organization" />
<item
android:id="@+id/navigation_business"
android:icon="@drawable/ic_business"
android:title="@string/title_business" />
<item
android:id="@+id/navigation_tasks"
android:icon="@drawable/ic_dashboard"
android:title="@string/title_tasks" />
</menu>
所有这些只是 BottomNavigationView 设置。现在要使其与 Navigation Arch Component 一起工作，您需要进入导航图编辑器，添加所有片段目的地（在我的例子中，我有 5 个，每个选项卡一个）并使用相同的设置目的地的 id navigation.xml 文件中的名称：
这将告诉 android 在选项卡和片段之间创建一个 link，现在每次用户单击 "Home" 选项卡时 android 都会处理加载正确的片段。
还需要将一段 kotlin 代码添加到您的 NavHost（主要 activity），以将内容与 BottomNavigationView:
你需要在你的onCreate中添加：
bottomNavigation.setupWithNavController(Navigation.findNavController(this, R.id.my_nav_host_fragment))
这告诉 android 在导航架构组件和 BottomNavigationView 之间进行连接。在 docs.
中查看更多信息要获得与使用 youtube 时相同的行为，只需添加：
navigation.setOnNavigationItemSelectedListener {item ->
onNavDestinationSelected(item, Navigation.findNavController(this, R.id.my_nav_host_fragment))
}
这将使目的地进入后退堆栈，因此当您点击后退按钮时，将弹出上次访问的目的地。
我制作了一个类似这样的应用程序（仍未在 PlayStore 上发布），它具有相同的导航功能，也许它的实现与 Google 在他们的应用程序中所做的不同，但功能是相同的。
结构涉及我有 Main Activity，我使用 showing/hiding 片段切换它的内容：
public void switchTo(final Fragment fragment, final String tag /*Each fragment should have a different Tag*/) {
// We compare if the current stack is the current fragment we try to show
if (fragment == getSupportFragmentManager().getPrimaryNavigationFragment()) {
return;
}
// We need to hide the current showing fragment (primary fragment)
final Fragment currentShowingFragment = getSupportFragmentManager().getPrimaryNavigationFragment();
final FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
if (currentShowingFragment != null) {
fragmentTransaction.hide(currentShowingFragment);
}
// We try to find that fragment if it was already added before
final Fragment alreadyAddedFragment = getSupportFragmentManager().findFragmentByTag(tag);
if (alreadyAddedFragment != null) {
// Since its already added before we just set it as primary navigation and show it again
fragmentTransaction.setPrimaryNavigationFragment(alreadyAddedFragment);
fragmentTransaction.show(alreadyAddedFragment);
} else {
// We add the new fragment and then show it
fragmentTransaction.add(containerId, fragment, tag);
fragmentTransaction.show(fragment);
// We set it as the primary navigation to support back stack and back navigation
fragmentTransaction.setPrimaryNavigationFragment(fragment);
}
fragmentTransaction.commit();
}
您必须像下面这样设置主机导航xml:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/colorPrimary" />
<fragment
android:id="@+id/navigation_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
app:defaultNavHost="true"
app:navGraph="@navigation/nav_graph" />
<android.support.design.widget.BottomNavigationView
android:id="@+id/bottom_navigation_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:itemIconTint="@drawable/color_state_list"
app:itemTextColor="@drawable/color_state_list"
app:menu="@menu/menu_bottom_navigation" />
</LinearLayout>
设置导航控制器：
NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.navigation_host_fragment);
NavigationUI.setupWithNavController(bottomNavigationView, navHostFragment.getNavController());
menu_bottom_navigation.xml :
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@id/tab1" // Id of navigation graph
android:icon="@mipmap/ic_launcher"
android:title="@string/tab1" />
<item
android:id="@id/tab2" // Id of navigation graph
android:icon="@mipmap/ic_launcher"
android:title="@string/tab2" />
<item
android:id="@id/tab3" // Id of navigation graph
android:icon="@mipmap/ic_launcher"
android:title="@string/tab3" />
</menu>
nav_graph.xml :
<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/nav_graph"
app:startDestination="@id/tab1">
<fragment
android:id="@+id/tab1"
android:name="com.navigationsample.Tab1Fragment"
android:label="@string/tab1"
tools:layout="@layout/fragment_tab_1" />
<fragment
android:id="@+id/tab2"
android:name="com.navigationsample.Tab2Fragment"
android:label="@string/tab2"
tools:layout="@layout/fragment_tab_2"/>
<fragment
android:id="@+id/tab3"
android:name="com.simform.navigationsample.Tab3Fragment"
android:label="@string/tab3"
tools:layout="@layout/fragment_tab_3"/>
</navigation>
通过设置与"nav_graph"相同的id到"menu_bottom_navigation"将处理底部导航的点击。
您可以在 action 标签中使用 popUpTo 属性 处理返回操作。
如果您有一个 bottomNavigationView，其中 3 个项目对应 3 个 Fragment：FragmentA、FragmentB 和 FragmentC，其中 FragmentA是导航图中的 startDestination，然后当您在 FragmentB 或 FragmentC 上并单击后退时，您将被重定向到 FragmentA，这就是Google 推荐的行为，默认情况下实现。
但是，如果您希望改变此行为，则需要按照其他一些答案的建议使用 ViewPager，或者您自己手动处理片段 backStack 和返回事务 - 这在一种方法会完全破坏导航组件的使用-。
首先，让我澄清一下 Youtube 和 Instagram 是如何处理片段导航的。
- 当用户位于详细信息片段上时，向后或向上弹出堆栈一次，并正确恢复状态。第二次点击已经选择的底部栏项目弹出所有堆栈到根，刷新它
- 当用户在根片段上时，返回到底部栏上最后选择的菜单，显示最后一个细节片段，状态正确恢复（JetPack 没有）
- 当用户在起始目标片段上时，返回完成 activity
None 以上其他答案使用喷气背包导航解决了所有这些问题。
JetPack 导航没有标准的方法来做到这一点，我发现更简单的方法是将导航 xml 图分成每个底部导航项，自己处理导航项之间的返回堆栈使用 activity FragmentManager 并使用 JetPack NavController 处理根片段和细节片段之间的内部导航（其实现使用 childFragmentManager 堆栈）。
假设您的 navigation 文件夹中有这 3 xmls:
res/navigation/
navigation_feed.xml
navigation_explore.xml
navigation_profile.xml
导航中的 destinationIds xml与 bottomNavigationBar 菜单 ids 相同。此外，对于每个 xml 将 app:startDestination 设置为您想要作为导航项根的片段。
创建 class BottomNavController.kt:
class BottomNavController(
val context: Context,
@IdRes val containerId: Int,
@IdRes val appStartDestinationId: Int
) {
private val navigationBackStack = BackStack.of(appStartDestinationId)
lateinit var activity: Activity
lateinit var fragmentManager: FragmentManager
private var listener: OnNavigationItemChanged? = null
private var navGraphProvider: NavGraphProvider? = null
interface OnNavigationItemChanged {
fun onItemChanged(itemId: Int)
}
interface NavGraphProvider {
@NavigationRes
fun getNavGraphId(itemId: Int): Int
}
init {
var ctx = context
while (ctx is ContextWrapper) {
if (ctx is Activity) {
activity = ctx
fragmentManager = (activity as FragmentActivity).supportFragmentManager
break
}
ctx = ctx.baseContext
}
}
fun setOnItemNavigationChanged(listener: (itemId: Int) -> Unit) {
this.listener = object : OnNavigationItemChanged {
override fun onItemChanged(itemId: Int) {
listener.invoke(itemId)
}
}
}
fun setNavGraphProvider(provider: NavGraphProvider) {
navGraphProvider = provider
}
fun onNavigationItemReselected(item: MenuItem) {
// If the user press a second time the navigation button, we pop the back stack to the root
activity.findNavController(containerId).popBackStack(item.itemId, false)
}
fun onNavigationItemSelected(itemId: Int = navigationBackStack.last()): Boolean {
// Replace fragment representing a navigation item
val fragment = fragmentManager.findFragmentByTag(itemId.toString())
?: NavHostFragment.create(navGraphProvider?.getNavGraphId(itemId)
?: throw RuntimeException("You need to set up a NavGraphProvider with " +
"BottomNavController#setNavGraphProvider")
)
fragmentManager.beginTransaction()
.setCustomAnimations(
R.anim.nav_default_enter_anim,
R.anim.nav_default_exit_anim,
R.anim.nav_default_pop_enter_anim,
R.anim.nav_default_pop_exit_anim
)
.replace(containerId, fragment, itemId.toString())
.addToBackStack(null)
.commit()
// Add to back stack
navigationBackStack.moveLast(itemId)
listener?.onItemChanged(itemId)
return true
}
fun onBackPressed() {
val childFragmentManager = fragmentManager.findFragmentById(containerId)!!
.childFragmentManager
when {
// We should always try to go back on the child fragment manager stack before going to
// the navigation stack. It's important to use the child fragment manager instead of the
// NavController because if the user change tabs super fast commit of the
// supportFragmentManager may mess up with the NavController child fragment manager back
// stack
childFragmentManager.popBackStackImmediate() -> {
}
// Fragment back stack is empty so try to go back on the navigation stack
navigationBackStack.size > 1 -> {
// Remove last item from back stack
navigationBackStack.removeLast()
// Update the container with new fragment
onNavigationItemSelected()
}
// If the stack has only one and it's not the navigation home we should
// ensure that the application always leave from startDestination
navigationBackStack.last() != appStartDestinationId -> {
navigationBackStack.removeLast()
navigationBackStack.add(0, appStartDestinationId)
onNavigationItemSelected()
}
// Navigation stack is empty, so finish the activity
else -> activity.finish()
}
}
private class BackStack : ArrayList<Int>() {
companion object {
fun of(vararg elements: Int): BackStack {
val b = BackStack()
b.addAll(elements.toTypedArray())
return b
}
}
fun removeLast() = removeAt(size - 1)
fun moveLast(item: Int) {
remove(item)
add(item)
}
}
}
// Convenience extension to set up the navigation
fun BottomNavigationView.setUpNavigation(bottomNavController: BottomNavController, onReselect: ((menuItem: MenuItem) -> Unit)? = null) {
setOnNavigationItemSelectedListener {
bottomNavController.onNavigationItemSelected(it.itemId)
}
setOnNavigationItemReselectedListener {
bottomNavController.onNavigationItemReselected(it)
onReselect?.invoke(it)
}
bottomNavController.setOnItemNavigationChanged { itemId ->
menu.findItem(itemId).isChecked = true
}
}
这样布局 main.xml：
<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">
<FrameLayout
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="0dp"
app:layout_constraintBottom_toTopOf="@id/bottomNavigationView"
app:layout_constraintTop_toTopOf="parent" />
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/bottomNavigationView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
app:layout_constraintBottom_toBottomOf="parent"
app:menu="@menu/navigation" />
</androidx.constraintlayout.widget.ConstraintLayout>
像这样在 activity 上使用：
class MainActivity : AppCompatActivity(),
BottomNavController.NavGraphProvider {
private val navController by lazy(LazyThreadSafetyMode.NONE) {
Navigation.findNavController(this, R.id.container)
}
private val bottomNavController by lazy(LazyThreadSafetyMode.NONE) {
BottomNavController(this, R.id.container, R.id.navigation_feed)
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.main)
bottomNavController.setNavGraphProvider(this)
bottomNavigationView.setUpNavigation(bottomNavController)
if (savedInstanceState == null) bottomNavController
.onNavigationItemSelected()
// do your things...
}
override fun getNavGraphId(itemId: Int) = when (itemId) {
R.id.navigation_feed -> R.navigation.navigation_feed
R.id.navigation_explore -> R.navigation.navigation_explore
R.id.navigation_profile -> R.navigation.navigation_profile
else -> R.navigation.navigation_feed
}
override fun onSupportNavigateUp(): Boolean = navController
.navigateUp()
override fun onBackPressed() = bottomNavController.onBackPressed()
}
Kotlin 中用于将底部导航项与导航图中的片段连接起来的短而好的代码：
val navControl = findNavController( R.id.nav_host_frag_main)
bottomNavigationView?.setupWithNavController(navControl)
*只是 consider:Bottom 导航图中的导航 ID 和片段必须具有相同的 ID。 还要感谢@sanat Answer
的良好解释最好的解决方案是由 google 团队在他的回购协议中提供的解决方案，后退按钮仍会将您送回第一个按钮，但其余行为是 "normal"... 看起来不幸的是 Google 仍然没有提供好的解决方案，即使他们在（youtube、Google 照片等）上使用它，他们说 androidx 可以提供帮助，但看起来就像我们四处寻找正常的解决方法。
这是他们使用导航的 link 到 google 回购。底部每个按钮都有一个 navGraph。 https://github.com/android/architecture-components-samples/blob/master/NavigationAdvancedSample/app/src/main/java/com/example/android/navigationadvancedsample/NavigationExtensions.kt 将这个文件复制到你的项目中，看看它是如何在他们的项目中实现的。对于后退按钮行为，您可以创建自己的堆栈，onBackpressed 只需在该堆栈上导航。
我没有找到任何官方解决方案，但我用自己的方式
首先，我为句柄片段创建 Stack
needToAddToBackStack : Boolen = true
private lateinit var fragmentBackStack: Stack<Int>
fragmentBackStack = Stack()
并在
navController.addOnDestinationChangedListener { _, destination, _ ->
if (needToAddToBackStack) {
fragmentBackStack.add(destination.id)
}
needToAddToBackStack = true
}
并处理后退按钮
override fun onBackPressed() {
if (::fragmentBackStack.isInitialized && fragmentBackStack.size > 1) {
fragmentBackStack.pop()
val fragmentId = fragmentBackStack.lastElement()
needToAddToBackStack = false
navController.navigate(fragmentId)
} else {
if (::fragmentBackStack.isInitialized && fragmentBackStack.size == 1) {
finish()
} else {
super.onBackPressed()
}
}
看完你的问题后，我再次检查了Google文档。我看到他们提供了一个解决方案，使 Navigation UI 与 BottomNavigationView 一起工作。所以，我为任何像我一样需要它的人创建了一个教程。 对于文本版本：https://nhatvm.com/how-to-use-navigationui-with-bottomnavigation-in-android/ 对于 youtube 版本：https://youtu.be/2uxILvBbkyY
在 Jetpack 导航中，您必须仅在单个导航图 xml 文件中进行更改以处理导航、处理后台堆栈、自定义动画、在片段之间传递参数。
如果您只想回到上一个片段，
<action
android:id="@+id/action_deleteEmployeeFragment_to_employeesListFragment2"
app:destination="@id/employeesListFragment"/>
btn_cancel.setOnClickListener {
it.findNavController().popBackStack()
}
如果你想清除所有的backstack并转到新的片段
<action
android:id="@+id/action_deleteEmployeeFragment_to_employeesListFragment2"
app:destination="@id/employeesListFragment"
app:popUpTo="@id/employeesListFragment"
app:popUpToInclusive="true"
app:launchSingleTop="true" />
btn_submit.setOnClickListener {
it.findNavController().navigate(DeleteEmployeeFragmentDirections.actionDeleteEmployeeFragmentToEmployeesListFragment2())
}
拥有一个适当的后栈来保持状态的关键是 NavHostFragment 有 childFragmentManager 和它们自己的后栈。 Navigation组件高级示例的扩展文件就是这样做的
/**
* Manages the various graphs needed for a [BottomNavigationView].
*
* This sample is a workaround until the Navigation Component supports multiple back stacks.
*/
fun BottomNavigationView.setupWithNavController(
navGraphIds: List<Int>,
fragmentManager: FragmentManager,
containerId: Int,
intent: Intent
): LiveData<NavController> {
// Map of tags
val graphIdToTagMap = SparseArray<String>()
// Result. Mutable live data with the selected controlled
val selectedNavController = MutableLiveData<NavController>()
var firstFragmentGraphId = 0
// First create a NavHostFragment for each NavGraph ID
navGraphIds.forEachIndexed { index, navGraphId ->
val fragmentTag = getFragmentTag(index)
// Find or create the Navigation host fragment
val navHostFragment = obtainNavHostFragment(
fragmentManager,
fragmentTag,
navGraphId,
containerId
)
// Obtain its id
val graphId = navHostFragment.navController.graph.id
if (index == 0) {
firstFragmentGraphId = graphId
}
// Save to the map
graphIdToTagMap[graphId] = fragmentTag
// Attach or detach nav host fragment depending on whether it's the selected item.
if (this.selectedItemId == graphId) {
// Update livedata with the selected graph
selectedNavController.value = navHostFragment.navController
attachNavHostFragment(fragmentManager, navHostFragment, index == 0)
} else {
detachNavHostFragment(fragmentManager, navHostFragment)
}
}
// Now connect selecting an item with swapping Fragments
var selectedItemTag = graphIdToTagMap[this.selectedItemId]
val firstFragmentTag = graphIdToTagMap[firstFragmentGraphId]
var isOnFirstFragment = selectedItemTag == firstFragmentTag
// When a navigation item is selected
setOnNavigationItemSelectedListener { item ->
// Don't do anything if the state is state has already been saved.
if (fragmentManager.isStateSaved) {
false
} else {
val newlySelectedItemTag = graphIdToTagMap[item.itemId]
if (selectedItemTag != newlySelectedItemTag) {
// Pop everything above the first fragment (the "fixed start destination")
fragmentManager.popBackStack(
firstFragmentTag,
FragmentManager.POP_BACK_STACK_INCLUSIVE
)
val selectedFragment = fragmentManager.findFragmentByTag(newlySelectedItemTag)
as NavHostFragment
// Exclude the first fragment tag because it's always in the back stack.
if (firstFragmentTag != newlySelectedItemTag) {
// Commit a transaction that cleans the back stack and adds the first fragment
// to it, creating the fixed started destination.
fragmentManager.beginTransaction()
.attach(selectedFragment)
.setPrimaryNavigationFragment(selectedFragment)
.apply {
// Detach all other Fragments
graphIdToTagMap.forEach { _, fragmentTagIter ->
if (fragmentTagIter != newlySelectedItemTag) {
detach(fragmentManager.findFragmentByTag(firstFragmentTag)!!)
}
}
}
.addToBackStack(firstFragmentTag)
.setCustomAnimations(
R.anim.nav_default_enter_anim,
R.anim.nav_default_exit_anim,
R.anim.nav_default_pop_enter_anim,
R.anim.nav_default_pop_exit_anim
)
.setReorderingAllowed(true)
.commit()
}
selectedItemTag = newlySelectedItemTag
isOnFirstFragment = selectedItemTag == firstFragmentTag
selectedNavController.value = selectedFragment.navController
true
} else {
false
}
}
}
// Optional: on item reselected, pop back stack to the destination of the graph
setupItemReselected(graphIdToTagMap, fragmentManager)
// Handle deep link
setupDeepLinks(navGraphIds, fragmentManager, containerId, intent)
// Finally, ensure that we update our BottomNavigationView when the back stack changes
fragmentManager.addOnBackStackChangedListener {
if (!isOnFirstFragment && !fragmentManager.isOnBackStack(firstFragmentTag)) {
this.selectedItemId = firstFragmentGraphId
}
// Reset the graph if the currentDestination is not valid (happens when the back
// stack is popped after using the back button).
selectedNavController.value?.let { controller ->
if (controller.currentDestination == null) {
controller.navigate(controller.graph.id)
}
}
}
return selectedNavController
}
private fun BottomNavigationView.setupDeepLinks(
navGraphIds: List<Int>,
fragmentManager: FragmentManager,
containerId: Int,
intent: Intent
) {
navGraphIds.forEachIndexed { index, navGraphId ->
val fragmentTag = getFragmentTag(index)
// Find or create the Navigation host fragment
val navHostFragment = obtainNavHostFragment(
fragmentManager,
fragmentTag,
navGraphId,
containerId
)
// Handle Intent
if (navHostFragment.navController.handleDeepLink(intent)
&& selectedItemId != navHostFragment.navController.graph.id
) {
this.selectedItemId = navHostFragment.navController.graph.id
}
}
}
private fun BottomNavigationView.setupItemReselected(
graphIdToTagMap: SparseArray<String>,
fragmentManager: FragmentManager
) {
setOnNavigationItemReselectedListener { item ->
val newlySelectedItemTag = graphIdToTagMap[item.itemId]
val selectedFragment = fragmentManager.findFragmentByTag(newlySelectedItemTag)
as NavHostFragment
val navController = selectedFragment.navController
// Pop the back stack to the start destination of the current navController graph
navController.popBackStack(
navController.graph.startDestination, false
)
}
}
private fun detachNavHostFragment(
fragmentManager: FragmentManager,
navHostFragment: NavHostFragment
) {
fragmentManager.beginTransaction()
.detach(navHostFragment)
.commitNow()
}
private fun attachNavHostFragment(
fragmentManager: FragmentManager,
navHostFragment: NavHostFragment,
isPrimaryNavFragment: Boolean
) {
fragmentManager.beginTransaction()
.attach(navHostFragment)
.apply {
if (isPrimaryNavFragment) {
setPrimaryNavigationFragment(navHostFragment)
}
}
.commitNow()
}
private fun obtainNavHostFragment(
fragmentManager: FragmentManager,
fragmentTag: String,
navGraphId: Int,
containerId: Int
): NavHostFragment {
// If the Nav Host fragment exists, return it
val existingFragment = fragmentManager.findFragmentByTag(fragmentTag) as NavHostFragment?
existingFragment?.let { return it }
// Otherwise, create it and return it.
val navHostFragment = NavHostFragment.create(navGraphId)
fragmentManager.beginTransaction()
.add(containerId, navHostFragment, fragmentTag)
.commitNow()
return navHostFragment
}
private fun FragmentManager.isOnBackStack(backStackName: String): Boolean {
val backStackCount = backStackEntryCount
for (index in 0 until backStackCount) {
if (getBackStackEntryAt(index).name == backStackName) {
return true
}
}
return false
}
private fun getFragmentTag(index: Int) = "bottomNavigation#$index"
这里重要的部分是如果NavHostFragment不存在于返回堆栈中，则使用上述函数将其添加到返回堆栈中。 commitNow 是同步的，不像 commit
私享乐趣obtainNavHostFragment( 片段管理器：片段管理器， 片段标签：字符串， navGraphId：整数， containerId: Int ): NavHostFragment { // 如果 Nav Host 片段存在，return 它 val existingFragment = fragmentManager.findFragmentByTag(fragmentTag) 作为 NavHostFragment？ existingFragment?.let { return 它 }
// Otherwise, create it and return it.
val navHostFragment = NavHostFragment.create(navGraphId)
fragmentManager.beginTransaction()
.add(containerId, navHostFragment, fragmentTag)
.commitNow()
return navHostFragment
}
我使用上面的 NavigationExtension 构建了一个，看起来像这样
嵌套导航。
导航图都差不多，我只加一个
nav_graph_home.xml
<?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"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/nav_graph_home"
app:startDestination="@id/homeFragment1">
<fragment
android:id="@+id/homeFragment1"
android:name="com.smarttoolfactory.tutorial5_3navigationui_bottomnavigation_nestednavigation.blankfragment.HomeFragment1"
android:label="HomeFragment1"
tools:layout="@layout/fragment_home1">
<action
android:id="@+id/action_homeFragment1_to_homeFragment2"
app:destination="@id/homeFragment2" />
</fragment>
<fragment
android:id="@+id/homeFragment2"
android:name="com.smarttoolfactory.tutorial5_3navigationui_bottomnavigation_nestednavigation.blankfragment.HomeFragment2"
android:label="HomeFragment2"
tools:layout="@layout/fragment_home2">
<action
android:id="@+id/action_homeFragment2_to_homeFragment3"
app:destination="@id/homeFragment3" />
</fragment>
<fragment
android:id="@+id/homeFragment3"
android:name="com.smarttoolfactory.tutorial5_3navigationui_bottomnavigation_nestednavigation.blankfragment.HomeFragment3"
android:label="HomeFragment3"
tools:layout="@layout/fragment_home3" >
<action
android:id="@+id/action_homeFragment3_to_homeFragment1"
app:destination="@id/homeFragment1"
app:popUpTo="@id/homeFragment1"
app:popUpToInclusive="true" />
</fragment>
</navigation>
底部导航菜单
menu_bottom_nav.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@+id/nav_graph_home"
android:icon="@drawable/ic_baseline_home_24"
android:title="Home"/>
<item
android:id="@+id/nav_graph_dashboard"
android:icon="@drawable/ic_baseline_dashboard_24"
android:title="Dashboard"/>
<item
android:id="@+id/nav_graph_notification"
android:icon="@drawable/ic_baseline_notifications_24"
android:title="Notification"/>
</menu>
包含 FragmentContainerView 和 BottomNavigationView
activiy_main.xml
<?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_container"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintBottom_toTopOf="@+id/bottom_nav"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/bottom_nav"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:menu="@menu/menu_bottom_nav" />
</androidx.constraintlayout.widget.ConstraintLayout>
MainActivity.kt
class MainActivity : AppCompatActivity() {
private var currentNavController: LiveData<NavController>? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
supportFragmentManager.addOnBackStackChangedListener {
val backStackEntryCount = supportFragmentManager.backStackEntryCount
val fragments = supportFragmentManager.fragments
val fragmentCount = fragments.size
Toast.makeText(
this,
"MainActivity backStackEntryCount: $backStackEntryCount, fragmentCount: $fragmentCount, fragments: $fragments",
Toast.LENGTH_SHORT
).show()
}
if (savedInstanceState == null) {
setupBottomNavigationBar()
} // Else, need to wait for onRestoreInstanceState
}
override fun onRestoreInstanceState(savedInstanceState: Bundle?) {
super.onRestoreInstanceState(savedInstanceState)
// Now that BottomNavigationBar has restored its instance state
// and its selectedItemId, we can proceed with setting up the
// BottomNavigationBar with Navigation
setupBottomNavigationBar()
}
/**
* Called on first creation and when restoring state.
*/
private fun setupBottomNavigationBar() {
val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottom_nav)
val navGraphIds = listOf(
R.navigation.nav_graph_home,
R.navigation.nav_graph_dashboard,
R.navigation.nav_graph_notification
)
// Setup the bottom navigation view with a list of navigation graphs
val controller = bottomNavigationView.setupWithNavController(
navGraphIds = navGraphIds,
fragmentManager = supportFragmentManager,
containerId = R.id.nav_host_container,
intent = intent
)
// Whenever the selected controller changes, setup the action bar.
controller.observe(this, Observer { navController ->
setupActionBarWithNavController(navController)
})
currentNavController = controller
}
override fun onSupportNavigateUp(): Boolean {
return currentNavController?.value?.navigateUp() ?: false
}
}
片段布局和 类 很简单 类 所以我跳过了它们 out.You 可以查看 full sample i built, or Google's repository 以检查高级导航或其他示例的扩展。
最初在这里回答：
在Jetpack Navigation Componenet中，如果你想在fragment弹出时执行一些操作，那么你需要覆盖以下函数。
将片段中的 OnBackPressedCallback 添加到 运行 按下后退时的特殊操作出现在底部的系统导航栏中。
override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) onBackPressedCallback = object : OnBackPressedCallback(true) { override fun handleOnBackPressed() { //perform your operation and call navigateUp findNavController().navigateUp() } } requireActivity().onBackPressedDispatcher.addCallback(onBackPressedCallback) }在片段中添加 onOptionsItemMenu 以处理应用内左上角的后退箭头按下。
override fun onViewCreated(view: View, savedInstanceState: Bundle?) { super.onViewCreated(view, savedInstanceState) setHasOptionsMenu(true) } override fun onOptionsItemSelected(item: MenuItem): Boolean { if (item.itemId == android.R.id.home) { //perform your operation and call navigateUp findNavController().navigateUp() return true } return super.onOptionsItemSelected(item) }如果在主机片段上按下后退时没有特殊代码 运行 则在 Activity.
中使用 onSupportNavigateUpoverride fun onSupportNavigateUp(): Boolean { if (navController.navigateUp() == false){ //navigateUp() returns false if there are no more fragments to pop onBackPressed() } return navController.navigateUp() }
请注意，如果片段包含 onOptionsItemSelected()
，则不会调用 onSupportNavigateUp()随着2.4.0版本的导航包，终于正式支持了！
https://developer.android.com/jetpack/androidx/releases/navigation#version_240_2
不仅如此：将导航库上传到此版本后，此功能是默认行为。作为旁注，现在此默认行为包括在片段之间导航时不会重新创建片段，