Question

Android Jetpack导航，BottomNavigationView在后退按钮上点击自动片段后退堆栈？

我想要的是，在用户一个接一个地选择多个标签后，用户点击后退按钮应用必须重定向到他/她打开的最后一页。

通过将当前选定的项目保存在ArrayList中，我使用Android ViewPager实现了相同的目标。 Android Jetpack导航发布后是否有任何自动后退堆栈？我想用导航图实现它

activity_main.xml中

<?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得到了一个答案，如下所示

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一次打开片段的实例。

为BottomNavigationView提供适当的后退导航

Answer 1

您真的不需要ViewPager来使用BottomNavigation和新的导航架构组件。我一直在使用一个使用两者的示例应用程序，请参阅here。

基本概念就是这样，你有一个主要活动来托管BottomNavigationView，这是导航图的导航主机，这就是xml的样子：

<强> activity_main.xml中

<?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（标签菜单）如下所示：

<强> 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。现在要使它与导航拱组件一起工作，你需要进入导航图编辑器，添加所有的片段目的地（在我的情况下，我有5个，每个选项卡一个），并设置目的地的ID相同将名称命名为navigation.xml文件中的名称：

这将告诉android在标签和片段之间建立链接，现在每次用户点击＆＃34; Home＆＃34; tab android将负责加载正确的片段。还有一段kotlin代码需要添加到您的NavHost（主要活动），以便与BottomNavigationView连接：

您需要添加onCreate：

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。请参阅docs。

中的详情

要获得使用youtube时的相同行为，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台，因此当您点击后退按钮时，将弹出最后一个访问过的目的地。

Answer 2

您必须像下面的xml那样设置主机导航：

<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>

使用导航控制器进行设置：

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>

通过将与“ nav_graph”相同的ID设置为“ menu_bottom_navigation”，可以处理底部导航的点击。

您可以使用popUpTo标签中的action属性处理后退动作。

Answer 3

您可以使用底部导航视图设置viewpager。 viewpager中的每个片段都是一个容器片段，它将具有带有自己的backstack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

Answer 4

首先，让我澄清一下YouTube和Instagram如何处理片段导航。

当用户使用详细信息片段时，向后或向上弹出堆栈一次，并正确恢复状态。再次单击已选择的底部栏项目，将所有堆栈弹出到根目录，刷新它
当用户使用根片段时，返回到底部栏中选择的最后一个菜单，显示最后一个细节片段，并正确恢复状态（JetPack不会）
当用户位于起始目标片段上时，后退会结束活动

以上所有其他答案都无法使用jetpack导航解决所有这些问题。

JetPack导航没有执行此操作的标准方法，我发现更简单的方法是将每个底部导航项目的导航xml图分为一个，使用活动FragmentManager自己处理导航项目之间的反向堆栈并使用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文件夹中有以下3个xml：

res/navigation/
    navigation_feed.xml
    navigation_explore.xml
    navigation_profile.xml

使导航xml中的destinationId与bottomNavigationBar菜单ID相同。另外，对于每个xml，将app:startDestination设置为您想要作为导航项目根目录的片段。

创建一个类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
    }
}

您的布局main.xml像这样：

<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>

像这样在您的活动中使用：

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()
}

Answer 5

导航包2.4.0版本终于正式支持了！

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，that seemed to be something quite requested。

Answer 6

我制作了一个具有相同导航的类似这样的应用程序（仍未在PlayStore上发布），也许其实现与Google在其应用程序中的实现不同，但是功能相同。

该结构涉及我的“主活动”，通过使用以下内容显示/隐藏片段来切换其内容：

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();
}

Answer 7

拥有适当的堆栈以保持状态的关键是拥有NavHostFragment的堆栈，该堆栈具有childFragmentManager和自己的堆栈。导航组件的高级示例的扩展文件实际上是这样做的。

/**
 * 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"

重要的部分是使用上面的函数获取NavHostFragment（如果它不存在于后堆栈中），并将其添加到后堆栈中。 commitNow是同步的，与commit

不同

私人乐趣getNavHostFragment（ fragmentManager：FragmentManager， fragmentTag：字符串， navGraphId：Int， containerId：整数）：NavHostFragment { //如果Nav Host片段存在，则将其返回 val existingFragment = fragmentManager.findFragmentByTag（fragmentTag）作为NavHostFragment吗？ existFragment？.let {返回}

// 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

具有嵌套导航。

导航图很相似，所以只有我加一个

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>

MainActivity的布局，其中包含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
    }
}

片段布局和类是简单的类，因此我跳过了它们。您可以检出自己构建的full sample或Google's repository来检查扩展的高级导航或其他示例。

Answer 8

如果您有一个bottomNavigationView，其中3个项目对应于3个Fragment：FragmentA，FragmentB和FragmentC，其中FragmentA是startDestination在导航图中，然后当您在FragmentB或FragmentC上单击时，将被重定向到FragmentA，这是推荐的行为由Google提供，并且默认情况下已实现。

但是，如果您希望更改此行为，则需要使用其他答案中建议的ViewPager，或者手动处理片段backStack并自己返回事务-通过某种方式会完全破坏对Navigation组件的使用。

Answer 9

Kotlin中简短而优质的代码将底部导航项与导航图中的片段连接起来：

    val navControl = findNavController( R.id.nav_host_frag_main)
    bottomNavigationView?.setupWithNavController(navControl)

*只需考虑：导航图中的底部导航ID和片段必须具有相同的ID。也要感谢@sanat答案

Answer 10

最好的解决方案是Google团队在其仓库中提供的解决方案，“后退”按钮仍将u发送回第一个按钮，但其余行为均显示为“正常” ...看来Google仍未提出建议一个很好的解决方案，即使他们在youtube，Google Photos等上使用它，他们也说androidx可以提供帮助，但是看起来就像我们四处寻找解决常规问题的方法一样。

这是他们使用导航的Google Repo的链接。每个按钮底部都有一个navGraph。 https://github.com/android/architecture-components-samples/blob/master/NavigationAdvancedSample/app/src/main/java/com/example/android/navigationadvancedsample/NavigationExtensions.kt将此文件复制到您的项目中，并查看其在项目中的实现方式。对于后退按钮行为，您可以创建自己的堆栈，而onBackpressed只需在该堆栈上导航即可。

Answer 11

我没有找到任何官方解决方案，但是我使用自己的方式

首先，我为处理片段创建堆栈

    needToAddToBackStack : Boolen = true


    private lateinit var fragmentBackStack: Stack<Int>
    fragmentBackStack = Stack()

和

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()
        }
    }

Answer 12

阅读您的问题后，我再次检查了Google文档。而且我看到他们提供了一种解决方案，可以使导航UI与BottomNavigationView一起正常工作。因此，我为像我一样需要它的任何人创建了一个教程。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

Answer 13

在jetpack导航中，您只需在单个导航图xml文件中进行更改即可进行句柄导航，句柄后退，自定义动画，在片段之间传递参数。

如果您只想返回上一个片段，

<action
        android:id="@+id/action_deleteEmployeeFragment_to_employeesListFragment2"
        app:destination="@id/employeesListFragment"/>


    btn_cancel.setOnClickListener {
                it.findNavController().popBackStack()
            }

如果要清除所有后退堆栈并转到新片段

<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())
        }

更多参考：Jetpack Navigation Example

Answer 14

最初在这里回答：https://stackoverflow.com/a/63645978/8956093

在Jetpack Navigation Componenet中，如果要在弹出片段时执行某些操作，则需要覆盖以下功能。

在片段中添加OnBackPressedCallback可以在底部的系统导航栏中按向后时运行特殊操作。

 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，以处理应用程序左上角出现的向后箭头按下。

 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back时没有特殊代码可运行，请在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（）

Android Jetpack导航，使用Youtube或Instagram的BottomNavigationView，如正确的后退导航（片段后退堆栈）？

14 个答案: