来自带有嵌套导航图的 arch 的新导航组件

Question

我有一个案例，希望通过arch navigation组件来实现。例如，我有 2 个导航图（主导航图和嵌套导航图）。我可以从嵌套调用主图吗？如何调用？

Answer 1

实际上正在工作，使用

val host: NavHostFragment? = (childFragmentManager.findFragmentById(R.id.main_app_fragment_container)  as NavHostFragment?)

我可以从主片段导航

Answer 2

重点是获得正确的 NavController 以在正确的图表中导航。我们以这个场景为例：

MainActivity
|- MainNavHost
   |- NavBarFragment
   |  |- NestedNavHost
   |  |  |-NestedContentFragment1
   |  |  |-NestedContentFragment2
   |  |
   |  |- BottomNavigationView
   |
   |- LoginFragment

主图和嵌套图位于单独的 xml 文件中：据我所知，这是必需的，因为导航针对不同的布局区域，因此它们需要两个不同的 NavHost秒。每个 Navhost 都需要通过 id 引用其图形，这要求它们位于不同的资源文件中。

关键是要在特定图形中导航，我们必须获得对正确图形所有者的引用：为此，调用 Navigation.findNavController(view) 时，view 参数至关重要。

文档说

NavHostFragments register their navigation controller at the root of their view subtree such that any descendant can obtain the controller instance through the Navigation helper class's methods

例如，如果在 NavBarFragment 中，我们写

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    navController = Navigation.findNavController(view)
}

这里的view是NestedNavHost的一个parent（也就是嵌套的NavHostFragment），不是后代，也就是说findNavController 将在树中向上游搜索，并将 return MainNavHost 的 NavController.

如果我们写

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    val nestedNavHostFragment = childFragmentManager.findFragmentById(R.id.nestedNavHostFragment) as? NavHostFragment
    navController = nestedNavHostFragment?.navController
}

其中nestedNavHostFragment是布局中FragmentContainerView的id，我们得到了正确的NestedNavHost的引用。注意使用 childFragmentManager，而不是 parentFragmentManager.

如果您仍在使用已弃用的 xml <fragment> 标签，您可以编写

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    val fragmentContainer = view.findViewById<View>(R.id.nestedNavHostFragment)
    navController = Navigation.findNavController(fragmentContainer)
}

其中 nestedNavHostFragment 是 <fragment> 标签的 ID。我们现在获得了对正确 NestedNavHost 的引用，因为我们传递给 findNavController 的视图属于 NestedNavHost 的子树。

同样，如果您需要从 NestedContentFragment 中获取对主 NavController 的引用，我们可以这样做：

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    // we can get the innermost NavController using this view,
    // because we are inside its subtree:
    nestedNavController = Navigation.findNavController(view)

    // we can find the outer NavController passing the owning Activity
    // and the id of a view associated to that NavController,
    // for example the NavHostFragment id:
    mainNavController = Navigation.findNavController(activity!!, R.id.mainNavHostFragment)
}

Answer 3

实际上，您可以使用 Global actions 从嵌套导航图目标导航到主导航图目标。

创建从嵌套导航图到主导航图中所需目的地的全局操作（在下图中突出显示）

示例：

<navigation android:id="@+id/main_nav_graph"
     ... >
     <fragment android:id="@+id/fragStart" .../>
     <fragment .../>
     <fragment .../>

     <navigation  android:id="@+id/nested_nav_graph">
           ...

     <!-- Global Action -->
     <action
         android:id="@+id/action_global_start"
         app:destination="@id/fragStart" />
     </navigation>

</navigation>

要导航到主图目标，请使用

findNavController().navigate(R.id.action_global_start)

Answer 4

我找到了解决内部NavController被覆盖问题的临时解决方案。您可以使用自定义 NavHostFragment，它为您提供所需的 navController。我的代码：

<androidx.fragment.app.FragmentContainerView
        ...
        android:name="MyNavHostFragment"
        app:defaultNavHost="false"
        app:navGraph="@navigation/inner_nav">
        ...
    </androidx.fragment.app.FragmentContainerView>

...

class MyNavHostFragment: NavHostFragment() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        MainFragment.innerNavController = navController
    }
}

...

class MainFragment : Fragment() {
    companion object{
        lateinit var innerNavController: NavController
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        val bottomNavigationView = 
             view!!.findViewById<BottomNavigationView>(R.id.bottom_navigation_view)
        bottomNavigationView.setupWithNavController(innerNavController)
    }
}

Answer 5

我使用 devrocca 提供的信息创建了一个答案。这是一个从头开始的完整答案，如果有人需要，我没有跳过任何内容。

这是导航的主要片段。相机是没有任何嵌套图的直接目的地，仪表板有它自己的嵌套图，但它被添加到相同的后台堆栈相机片段被添加。主页有 3 个片段及其自己的导航主机

MainActivity
|- MainNavHost
   |- HomeNavHostFragment
   |  |- NestedNavHost
   |     |-HomeFragment1
   |     |-HomeFragment2
   |     |-HomeFragment3
   |  
   |- nav_graph_dashboard 
   |
   |- CameraFragment

这是导航文件

主导航nav_graph.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"
        app:startDestination="@id/main_dest">

    <!-- MainFragment-->
    <fragment
            android:id="@+id/main_dest"
            android:name="com.smarttoolfactory.tutorial1_3navigation_nestednavhost.blankfragment.MainFragment"
            android:label="MainFragment"
            tools:layout="@layout/fragment_main">

        <!-- Camera -->
        <action
                android:id="@+id/action_main_dest_to_cameraFragment"
                app:destination="@id/cameraFragment" />

        <!-- Home NavGraph -->
        <action
                android:id="@+id/action_main_dest_to_nav_graph_home"
                app:destination="@id/nav_graph_home" />

        <!-- Dashboard  NavGraph-->
        <action
                android:id="@+id/action_main_dest_to_nav_graph_dashboard"
                app:destination="@id/nav_graph_dashboard" />

    </fragment>

    <!-- Camera -->
    <fragment
            android:id="@+id/cameraFragment"
            android:name="com.smarttoolfactory.tutorial1_3navigation_nestednavhost.blankfragment.CameraFragment"
            android:label="CameraFragment" />


    <!-- Home-->
    <include app:graph="@navigation/nav_graph_home" />

    <!-- Dashboard-->
    <include app:graph="@navigation/nav_graph_dashboard" />


    <!-- Global Action Start -->
    <action
            android:id="@+id/action_global_start"
            app:destination="@id/main_dest"
            app:popUpTo="@id/main_dest"
            app:popUpToInclusive="true" />


</navigation>

仪表板嵌套导航图

<?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_dashboard"
        app:startDestination="@id/dashboard_dest">

    <fragment
            android:id="@+id/dashboard_dest"
            android:name="com.smarttoolfactory.tutorial1_3navigation_nestednavhost.blankfragment.DashboardFragment1"
            android:label="DashboardFragment1"
            tools:layout="@layout/fragment_dashboard1">
        <action
                android:id="@+id/action_dashboardFragment1_to_dashboardFragment2"
                app:destination="@id/dashboardFragment2" />
    </fragment>

    <fragment
            android:id="@+id/dashboardFragment2"
            android:name="com.smarttoolfactory.tutorial1_3navigation_nestednavhost.blankfragment.DashboardFragment2"
            android:label="DashboardFragment2"
            tools:layout="@layout/fragment_dashboard2">
    </fragment>

</navigation>

以及带有自己的 NavHost 的嵌套导航图 nav_graph_home

<?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/home_dest">

    <fragment
            android:id="@+id/home_dest"
            android:name="com.smarttoolfactory.tutorial1_3navigation_nestednavhost.blankfragment.HomeNavHostFragment"
            android:label="HomeHost"
            tools:layout="@layout/fragment_home_navhost" />

    <fragment
            android:id="@+id/homeFragment1"
            android:name="com.smarttoolfactory.tutorial1_3navigation_nestednavhost.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.tutorial1_3navigation_nestednavhost.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.tutorial1_3navigation_nestednavhost.blankfragment.HomeFragment3"
            android:label="HomeFragment3"
            tools:layout="@layout/fragment_home3" />

</navigation>

布局，我只添加必要的布局，其他的是带有按钮的简单布局，我添加 link 用于包含其他导航组件示例的示例项目。

MainActivity


<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto">

    <androidx.coordinatorlayout.widget.CoordinatorLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">


        <com.google.android.material.appbar.AppBarLayout
                android:id="@+id/appbar"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

            <androidx.appcompat.widget.Toolbar
                    android:id="@+id/toolbar"
                    android:layout_width="match_parent"
                    android:layout_height="?attr/actionBarSize"
                    app:popupTheme="@style/ThemeOverlay.AppCompat.ActionBar" />

        </com.google.android.material.appbar.AppBarLayout>

        <androidx.constraintlayout.widget.ConstraintLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                app:layout_behavior="@string/appbar_scrolling_view_behavior">

            <androidx.fragment.app.FragmentContainerView
                    android:id="@+id/main_nav_host_fragment"
                    android:name="androidx.navigation.fragment.NavHostFragment"
                    android:layout_width="0dp"
                    android:layout_height="0dp"
                    app:layout_constraintLeft_toLeftOf="parent"
                    app:layout_constraintRight_toRightOf="parent"
                    app:layout_constraintTop_toTopOf="parent"
                    app:layout_constraintBottom_toBottomOf="parent"

                    app:defaultNavHost="true"
                    app:navGraph="@navigation/nav_graph"/>

        </androidx.constraintlayout.widget.ConstraintLayout>

    </androidx.coordinatorlayout.widget.CoordinatorLayout>

</layout>

主片段，这是图像中显示的第一个片段，用作主导航的开始

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto">

    <androidx.constraintlayout.widget.ConstraintLayout
            android:id="@+id/parentLayout"
            android:layout_width="match_parent"
            android:layout_height="match_parent">

        <Button
                android:id="@+id/btnDestCam"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Destination Camera"
                app:layout_constraintBottom_toTopOf="@+id/btnNavGraphHome"
                app:layout_constraintHorizontal_bias="0.5"
                app:layout_constraintLeft_toRightOf="parent"
                app:layout_constraintRight_toLeftOf="parent"
                app:layout_constraintTop_toTopOf="parent" />

        <Button
                android:id="@+id/btnNavGraphHome"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Nested NavHost Graph Home"
                app:layout_constraintBottom_toTopOf="@+id/btnNavGraphDashboard"
                app:layout_constraintHorizontal_bias="0.5"
                app:layout_constraintLeft_toRightOf="parent"
                app:layout_constraintRight_toLeftOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/btnDestCam" />

        <Button
                android:id="@+id/btnNavGraphDashboard"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Nested Graph Dashboard"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintHorizontal_bias="0.5"
                app:layout_constraintLeft_toRightOf="parent"
                app:layout_constraintRight_toLeftOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/btnNavGraphHome" />


    </androidx.constraintlayout.widget.ConstraintLayout>


</layout>

包含用于主页导航的内部 NavHostFragment 的布局

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto">

    <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">

        <androidx.fragment.app.FragmentContainerView
                android:id="@+id/nested_nav_host_fragment"
                android:name="androidx.navigation.fragment.NavHostFragment"
                android:layout_width="0dp"
                android:layout_height="0dp"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toTopOf="parent"

                app:defaultNavHost="false"
                app:navGraph="@navigation/nav_graph_home" />

    </androidx.constraintlayout.widget.ConstraintLayout>

</layout>

MainActivity 用于检查主导航返回堆栈，这里重要的是

supportFragmentManager 返回堆栈不会在您导航它的 childFragmentManager 时更新，即使对于主导航，即使您只有一个

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // Get NavHostFragment
        val navHostFragment =
            supportFragmentManager.findFragmentById(R.id.main_nav_host_fragment)

        // ChildFragmentManager of NavHostFragment
        val navHostChildFragmentManager = navHostFragment?.childFragmentManager

        navHostChildFragmentManager?.addOnBackStackChangedListener {

            val backStackEntryCount = navHostChildFragmentManager.backStackEntryCount
            val fragments = navHostChildFragmentManager.fragments
        }
    }
}

包含主页导航主机的片段

class HomeNavHostFragment : BaseDataBindingFragment<FragmentHomeNavhostBinding>() {
    override fun getLayoutRes(): Int = R.layout.fragment_home_navhost

    private var navController: NavController? = null

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        val nestedNavHostFragment =
            childFragmentManager.findFragmentById(R.id.nested_nav_host_fragment) as? NavHostFragment
        navController = nestedNavHostFragment?.navController

        navController?.navigate(R.id.homeFragment1)

        listenBackStack()
    }

    private fun listenBackStack() {

        // Get NavHostFragment
        val navHostFragment =
            childFragmentManager.findFragmentById(R.id.nested_nav_host_fragment)

        // ChildFragmentManager of the current NavHostFragment
        val navHostChildFragmentManager = navHostFragment?.childFragmentManager

        navHostChildFragmentManager?.addOnBackStackChangedListener {

            val backStackEntryCount = navHostChildFragmentManager!!.backStackEntryCount
            val fragments = navHostChildFragmentManager!!.fragments

            Toast.makeText(
                requireContext(),
                "HomeNavHost backStackEntryCount: $backStackEntryCount, fragments: $fragments",
                Toast.LENGTH_SHORT
            ).show()
        }


        val callback = object : OnBackPressedCallback(true) {
            override fun handleOnBackPressed() {

                val backStackEntryCount = navHostChildFragmentManager!!.backStackEntryCount

                Toast.makeText(
                    requireContext(),
                    "HomeNavHost backStackEntryCount: $backStackEntryCount",
                    Toast.LENGTH_SHORT
                ).show()


        if (backStackEntryCount == 1) {
                OnBackPressedCallback@ this.isEnabled = false
                requireActivity().onBackPressed()
            } else {
                navController?.navigateUp()
            }
        }
        }

        requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner, callback)

    }
}

有一件事我不知道它是否在图形或嵌套的 NavHostFragment 代码中有所改进

如果您将起始目的地设置为 nav_graph_home HomeFragment1 而不是 HomeNavHostFragment，它将作为仪表板工作，忽略嵌套的 NavHost 并添加到片段的主后台堆栈。

因为您在任何主片段中的内部 NavHostFragment findNavController() returns 内部片段

class HomeFragment3 : BaseDataBindingFragment<FragmentHome3Binding>() {
    override fun getLayoutRes(): Int = R.layout.fragment_home3

    private var count = 0

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        dataBinding.btnIncrease.setOnClickListener {
            dataBinding.tvTitle.text = "Count: ${count++}"
        }


        val mainNavController =
            Navigation.findNavController(requireActivity(), R.id.main_nav_host_fragment)

        dataBinding.btnGoToStart.setOnClickListener {

            // Using destination belong to main_nav_host with nested navHost causes app to crash
//            findNavController().navigate(R.id.action_global_start)

            mainNavController.navigate(R.id.action_global_start)/**/
        }
    }
}

您也可以使用全局操作，但这不是必需的，因为如果您不使用 OnBackPressed.

，内部 navHost 中的后退导航会直接将您带回主导航

Link 用于 full example 和其他导航组件示例，如果您有兴趣。

Answer 6

我们可以通过找到根导航主机控制器然后通过根导航主机控制器导航来实现它

val Fragment.findRootNavHost: NavController?
get() = this.activity?.let { 
    Navigation.findNavController(it, your_root_fragment_id) 
}

findRootNavHost?.navigate(`your_destination_fragment_id`)

请查看 medium 文章 link Github 相同的回购

来自带有嵌套导航图的 arch 的新导航组件

New navigation component from arch with nested navigation graph

android

android-navigation

android-architecture-components

android-jetpack