Back button not working on Preferences multiple screens

Question

I am trying to implement preferences using multiple screens. The action bar back button only returns to MainActivity even for sub preference screens. For example, I have a root preference screen and then a sub reference screen. The back button on the root preference screen goes back to the main activity as expected. But the back button on the sub reference screen also goes back to the main activity rather than the root preference screen. Below is a code dump because I'm not sure what I am doing wrong. Thanks.

Androidmanifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.PreferencesTest">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".SettingsActivity2"
            android:label="@string/title_activity_settings2"
            android:parentActivityName=".SettingsActivity">
            <meta-data
                android:name="android.support.PARENT_ACTIVITY"
                android:value=".SettingsActivity" />
        </activity>
        <activity
            android:name=".SettingsActivity"
            android:label="@string/title_activity_settings"
            android:parentActivityName=".MainActivity">
            <meta-data
                android:name="android.support.PARENT_ACTIVITY"
                android:value=".MainActivity" />
        </activity>
        <activity
            android:name=".MainActivity"
            android:theme="@style/AppTheme.Launcher">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

MainActivity.kt

class MainActivity : AppCompatActivity()
{
    override fun onCreate(savedInstanceState: Bundle?)
    {
        setTheme(R.style.AppTheme)
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    //Inflates settings menu button
    override fun onCreateOptionsMenu(menu: Menu): Boolean
    {
        val inflater: MenuInflater = menuInflater
        inflater.inflate(R.menu.settings_menu, menu)
        return true
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean
    {
        return when(item.itemId)
        {
            R.id.action_settings ->
            {
                val intent = Intent(this, SettingsActivity::class.java)
                startActivity(intent)
                true
            }
            else -> super.onOptionsItemSelected(item)
        }
    }
}

SettingsActivity.kt

class SettingsActivity : AppCompatActivity()
{

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

        supportFragmentManager
            .beginTransaction()
            .replace(R.id.settings, SettingsFragment())
            .commit()

        supportActionBar?.setDisplayHomeAsUpEnabled(true)

    }

    class SettingsFragment : PreferenceFragmentCompat()
    {
        override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?)
        {
            setPreferencesFromResource(R.xml.root_preferences, rootKey)
        }
    }
}

SettingsActivity2.kt

class SettingsActivity2 : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.settings_activity)
        supportFragmentManager
            .beginTransaction()
            .replace(R.id.settings, SettingsFragment())
            .commit()
        supportActionBar?.setDisplayHomeAsUpEnabled(true)
    }

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

res > menu > settings_menu.xml

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

    <item
        android:id="@+id/action_settings"
        android:orderInCategory="100"
        android:title="Settings"
        app:showAsAction="ifRoom" />

</menu>

res > xml > root_preferences.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">
    <Preference
        android:fragment="com.example.PreferencesTest.SettingsActivity2$SettingsFragment"
        android:title="Title"
        android:summary="Summary">
        <extra
            android:name="name"
            android:value="preferences2" />
    </Preference>
</PreferenceScreen>

res > xml > 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">
    <EditTextPreference
        app:key="callNumber"
        app:title="Call Number"
        android:inputType="phone"
        app:useSimpleSummaryProvider="true" />
</PreferenceScreen>

Answer 1

Found a good complete example here https://github.com/googlearchive/android-preferences

Answer 2

You need to override the default behavior of android.R.id.home to onBackPressed.

class SettingsActivity : AppCompatActivity() {

    ...

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        return when (item.itemId) {
            android.R.id.home -> {
                onBackPressed()
                true
            }
            else -> super.onOptionsItemSelected(item)
        }
    }

    ...