为什么当我第二次在Android Studio中使用导航启动动作时，导航目的地丢失了？

Question

我在项目中使用导航。

[图像1将在应用程序启动时显示，在图像1中单击下一步按钮，将显示图像2，然后在图像2中单击返回按钮，将再次显示图像1。

现在，我再次单击图像1中的“下一步”按钮，应用程序崩溃，出现错误'此NavController未知的导航目标com.example.myapplication：id / actionTwo，'>>，为什么？

为什么NavHostFragment.findNavController(this).navigate(OneFrDirections.actionTwo())无法第二次启动？

您可以在https://www.dropbox.com/s/1ad47eqi4iwig5v/MyNAV.zip?dl=0下载测试代码

my.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"
    android:id="@+id/my"
    app:startDestination="@+id/One">

    <fragment
        android:id="@+id/One"
        android:name="com.example.myapplication.OneFr"
        android:label="One">

        <action
            android:id="@+id/actionTwo"
            app:destination="@id/Two" />

    </fragment>

    <fragment
        android:id="@+id/Two"
        android:name="com.example.myapplication.TwoFr"
        android:label="Two">

        <action
            android:id="@+id/actionOne"
            app:destination="@id/One" />
    </fragment>

</navigation>
OneFr.kt

class OneFr : Fragment() 
    override fun onCreate(savedInstanceState: Bundle?) 
        super.onCreate(savedInstanceState)

    

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?): View? =
        inflater.inflate(R.layout.one, container, false)


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

         view.findViewById<Button>(R.id.btnNext).setOnClickListener 
            NavHostFragment.findNavController(this).navigate(OneFrDirections.actionTwo())
        

    


TwoFr.kt

class TwoFr : Fragment() 
    override fun onCreate(savedInstanceState: Bundle?) 
        super.onCreate(savedInstanceState)
    

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?): View? =
        inflater.inflate(R.layout.two, container, false)


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

        // Handle back button press
        view.findViewById<Button>(R.id.btnBack).setOnClickListener 
            fragmentManager?.popBackStack()
        

    


one.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">

    <Button
        android:id="@+id/btnNext"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Next"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>
two.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">

    <Button
        android:id="@+id/btnBack"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Back"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>
activity_main.xml

<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:keepScreenOn="true"
    tools:context=".MainActivity">

    <fragment
        android:id="@+id/fragment_container"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/my" />

</FrameLayout>
MainActivity.kt

class MainActivity : AppCompatActivity() 

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

图像1

图像2

我在项目中使用导航。应用启动时将显示图像1，单击图像1中的“下一步”按钮，将显示图像2，然后单击图像2中的“后退”按钮，图像1将...