菜单项未显示在片段拥有的操作栏中

Question

每个片段都包含其自己的应用栏，该应用栏已成功显示，但菜单项未在其工具栏中显示。 因此，有一个带有底部导航栏的主要活动，还有一个主容器片段，其中不同的片段将根据选定的底部导航而膨胀。一切正常，但菜单未显示在其工具栏中。

activity_main.xml具有NavHostFragment和BottomNavigationView

<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:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".activities.MainActivity">

    <fragment
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:id="@+id/host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        app:navGraph="@navigation/mobile_navigation"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:defaultNavHost="true" />

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/navigation"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginEnd="0dp"
        android:orientation="horizontal"
        android:background="?android:attr/windowBackground"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/navigation" />

</androidx.constraintlayout.widget.ConstraintLayout>

mobile_navigation（有两个目的地）

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/mobile_navigation"
    app:startDestination="@id/firstFragment">

    <fragment
        android:id="@+id/firstFragment"
        android:name="com.example.user.FirstFragment"
        android:label="@string/app_name" />

    <fragment
        android:id="@+id/secondFragment"
        android:name="com.example.user.SecondFragment"
        android:label="@string/second_fragment" />
</navigation>

MainActivity

class MainActivity : AppCompatActivity() {

    override fun onSupportNavigateUp() = findNavController(R.id.host_fragment).navigateUp()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)
        navigation.setupWithNavController(findNavController(R.id.host_fragment))
   }

}

first_fragment.xml和CollapsingToolbarLayout

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout 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=".FirstFragment">

    <com.google.android.material.appbar.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="140dp">

        <com.google.android.material.appbar.CollapsingToolbarLayout
            android:id="@+id/collapsingToolbar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_scrollFlags="exitUntilCollapsed|scroll">

            <androidx.appcompat.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize" />
        </com.google.android.material.appbar.CollapsingToolbarLayout>
    </com.google.android.material.appbar.AppBarLayout>

</androidx.coordinatorlayout.widget.CoordinatorLayout>

FirstFragment

class FirstFragment : Fragment() {

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        var view = inflater.inflate(R.layout.first_fragment, container, false)
        setHasOptionsMenu(true)
        return view
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        collapsingToolbar.setupWithNavController(toolbar, findNavController())

    }

    override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
        inflater.inflate(R.menu.navigation, menu)
    }

}