Android ThemeLibrary

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.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="package.SettingsActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

    </android.support.design.widget.AppBarLayout>

    <fragment
        android:layout_marginTop="?attr/actionBarSize"
        android:id="@+id/settings_fragment"
        android:name="package.SettingsFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />


</android.support.design.widget.CoordinatorLayout>

class SettingsActivity : AppCompatActivity() {

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

        ThemeUtils.initialize(this)

        setContentView(R.layout.activity_settings)
        setSupportActionBar(toolbar)

        supportActionBar?.setDisplayHomeAsUpEnabled(true)
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {

        if (item.itemId == android.R.id.home) {
            onBackPressed()
        }

        return super.onOptionsItemSelected(item)
    }

}

class SettingsFragment: PreferenceFragmentCompat(),
        SharedPreferences.OnSharedPreferenceChangeListener{

    override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?) {
        // Add 'general' preferences, defined in the XML file
        addPreferencesFromResource(R.xml.pref_general)

        val sharedPreferences = preferenceScreen.sharedPreferences

        val count = preferenceScreen.preferenceCount

        (0 until count)
                .asSequence()
                .map { preferenceScreen.getPreference(it) }
                .forEach {
                    when (it) {
                        is CheckBoxPreference -> {
                            val value = sharedPreferences.getBoolean(it.key, false)
                            setPreferenceSummery(it, value)
                        }
                        else -> {
                            val value = sharedPreferences.getString(it.key, "")
                            setPreferenceSummery(it, value)
                        }
                    }
                }
    }

    override fun onSharedPreferenceChanged(sharedPreferences: SharedPreferences?, key: String?) {

        val preference = findPreference(key)

        if (preference != null) {

            if (preference !is CheckBoxPreference) {
                val value = sharedPreferences?.getString(preference.key, "") ?: ""
                setPreferenceSummery(preference, value)
            }
        }
    }

    private fun setPreferenceSummery(preference: Preference, value: Any) {

        val stringValue = value.toString()

        if (preference is ListPreference) {

            val prefIndex = preference.findIndexOfValue(stringValue)

            if (prefIndex >= 0) {
                preference.summary = preference.entries[prefIndex]
            }
        } else {
            // For other preferences, set the summary to the value's simple string representation.
            preference.summary = stringValue
        }
    }

    override fun onStart() {
        super.onStart()
        preferenceScreen.sharedPreferences.registerOnSharedPreferenceChangeListener(this)
    }
}