PreferenceFragments not in the same FragmentManager?

问题

We have a PreferenceFragmentCompat, and with a tap on a preference, we want to switch from the current PreferenceFragmentCompat to a new PreferenceFragmentCompat. (To have certain settings on a new screen).

However, regardless of what we have tried, we keep running into the following error:

Fragment declared target fragment that does not belong to this FragmentManager

MainActivity.kt

class MainActivity : AppCompatActivity(), ActivityCompat.OnRequestPermissionsResultCallback, PreferenceFragmentCompat.OnPreferenceStartFragmentCallback {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val navView: BottomNavigationView = findViewById(R.id.nav_view)

        val navController = findNavController(R.id.nav_host_fragment)
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        val appBarConfiguration = AppBarConfiguration(
            setOf(
                R.id.navigation_home, R.id.navigation_dashboard, R.id.navigation_preferences
            )
        )

        setupActionBarWithNavController(navController, appBarConfiguration)
        navView.setupWithNavController(navController)
    }

    override fun onPreferenceStartFragment(caller: PreferenceFragmentCompat, pref: Preference): Boolean {
        val args = pref.extras
        val fragment = supportFragmentManager.fragmentFactory.instantiate(
            classLoader,
            pref.fragment)
        fragment.arguments = args
        fragment.setTargetFragment(caller, 0)
        // Replace the existing Fragment with the new Fragment
        supportFragmentManager.beginTransaction()
            .replace(R.id.nav_host_fragment, fragment)
            .addToBackStack(null)
            .commit()
        return true
    }
}

PreferenceFragement1.kt

class PreferencesFragment1 : PreferenceFragmentCompat() {

    override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?) {
        setPreferencesFromResource(R.xml.preferences1, rootKey)
    }
}

PreferenceFragment2.kt

class PreferenceFragment2 : PreferenceFragmentCompat() {

    override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?) {
        setPreferencesFromResource(R.xml.preferences2, rootKey)
    }
}

Preferences1.xml

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen 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">

    <PreferenceCategory
        android:title="Category"
        app:iconSpaceReserved="false">

        <Preference
            app:key="pref2"
            app:iconSpaceReserved="false"
            android:title="Open"
            app:fragment="com.testapp.ui.preferences.Preference2"/>

    </PreferenceCategory>
</PreferenceScreen>

Preferences2.xml

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen 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">
</PreferenceScreen>

The stacktrace shows the following:

java.lang.IllegalStateException: Fragment Preference2{496ebb9} (1b91d8df-58c0-485a-96f9-d392fcef528b) id=0x7f09008d} declared target fragment Preference1{b6337c1} (97aa1b0e-d5fa-4995-b0ba-e89ad0ea5ce0) id=0x7f09008d} that does not belong to this FragmentManager!
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1148)
        at androidx.fragment.app.FragmentTransition.addToFirstInLastOut(FragmentTransition.java:1255)
        at androidx.fragment.app.FragmentTransition.calculateFragments(FragmentTransition.java:1138)
        at androidx.fragment.app.FragmentTransition.startTransitions(FragmentTransition.java:136)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1989)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1947)
        at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1849)
        at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6718)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:491)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

We are using androidx.preference:preference-ktx:1.1.1. Can some give us a concise explanation what exactly is causing this problem, and how we can solve it?

We already looked at the following (related) posts, without any success:

• Fragment declared target fragment that does not belong to this FragmentManager
• How to open a new PreferenceFragment from current one, using the new Android-X API?
• https://developer.android.com/guide/topics/ui/settings/organize-your-settings

回答1:

When you create a Fragment via the navigation graph, it is a child fragment of the NavHostFragment. It specifically is not the activity's supportFragmentManager. This is why the target fragment isn't found - you're using the wrong FragmentManager.

However, you should not use app:fragment or onPreferenceStartFragment when you're using Navigation. Instead, your PreferencesFragment1 should set a click listener on your Preference and have it call navigate() directly.

class PreferencesFragment1 : PreferenceFragmentCompat() {

    override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?) {
        setPreferencesFromResource(R.xml.preferences1, rootKey)
        findPreference<Preference>("pref2")?.setOnPreferenceClickListener {
            // Use whatever ID that is associated with
            // PreferenceFragment2 in your navigation graph
            findNavController().navigate(R.id.pref2)
        }
    }
}

Preferences1.xml

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen 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">

    <PreferenceCategory
        android:title="Category"
        app:iconSpaceReserved="false">

        <Preference
            app:key="pref2"
            app:iconSpaceReserved="false"
            android:title="Open"/>

    </PreferenceCategory>
</PreferenceScreen>

来源：https://stackoverflow.com/questions/63305040/preferencefragments-not-in-the-same-fragmentmanager