Android架构组件导航：工具栏后退按钮缺失，后退不起作用

我正在尝试喷气背包导航，但当我移动到新片段时无法显示导航后退按钮。

导航活动.kt

class NavActivity : AppCompatActivity() {

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

        val toolbar = findViewById<Toolbar>(R.id.toolbar)
        setSupportActionBar(toolbar)

        val host: NavHostFragment = supportFragmentManager
                .findFragmentById(R.id.navigation_graph) as NavHostFragment? ?: return

        // Set up Navigation
        val navController = host.navController
        setupActionBarWithNavController(navController)
        setupBottomNavMenu(navController)

    }

    private fun setupActionBarWithNavController(navController: NavController) {
        setupActionBarWithNavController(this, navController)
    }

    private fun setupBottomNavMenu(navController: NavController) {
        findViewById<BottomNavigationView>(R.id.bottom_nav_view)?.let { bottomNavView ->
            NavigationUI.setupWithNavController(bottomNavView, navController)
        }
    }

}

活动导航.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=".views.NavActivity">

<androidx.appcompat.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_height="?attr/actionBarSize"
    android:elevation="4dp"
    android:background="?attr/colorPrimary"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    android:theme="@style/ThemeOverlay.AppCompat.ActionBar"
    app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
    android:layout_width="match_parent">
</androidx.appcompat.widget.Toolbar>
<fragment
    android:id="@+id/navigation_graph"
    android:name="androidx.navigation.fragment.NavHostFragment"
    android:layout_width="0dp"
    android:layout_height="0dp"
    app:defaultNavHost="true"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/toolbar"
    app:navGraph="@navigation/navigation_graph"/>

<com.google.android.material.bottomnavigation.BottomNavigationView
    android:id="@+id/bottom_nav_view"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:menu="@menu/menu_bottom_nav" />

导航图.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"
    app:startDestination="@+id/launcher_home">
    <fragment
        android:id="@+id/launcher_home"
        android:name="com.noisyninja.androidlistpoc.views.main.MainFragment"
        android:label="@string/app_name"
        tools:layout="@layout/fragment_main">

        <action
            android:id="@+id/next_action"
            app:destination="@+id/detailFragment"
            app:enterAnim="@anim/slide_in_right"
            app:exitAnim="@anim/slide_out_left"
            app:popEnterAnim="@anim/slide_in_left"
            app:popExitAnim="@anim/slide_out_right" />

    </fragment>

    <fragment
        android:id="@+id/detailFragment"
        android:name="com.noisyninja.androidlistpoc.views.detail.DetailFragment"
        android:label="DetailFragment" />
</navigation>

导航代码：

    /**
     * opens detail activity
     */
    override fun showDetail(view: View, me: Me) {

        var bundle = Bundle()
        bundle.putString("key", "value")
        Navigation.findNavController(view).navigate(R.id.next_action, bundle, null)
    }

如上所述，当导航到第二个片段时，工具栏完全丢失并且不显示后退按钮。 点击硬件后退按钮也不会弹出详细视图。 第一次点击没有效果，第二次点击退出应用程序。

Override您的 Activity 中的此方法nav_host_fragment

@Override
    public boolean onSupportNavigateUp() {
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        return NavigationUI.navigateUp(navController, mAppBarConfiguration)
                || super.onSupportNavigateUp();
    }