StringDelegate.kt

class StringPreference(
    private val preferences: SharedPreferences,
    private val name: String,
    private val defaultValue: String
) : ReadWriteProperty<Any, String?> {

    @WorkerThread
    override fun getValue(thisRef: Any, property: KProperty<*>) =
        preferences.getString(name, defaultValue) ?: defaultValue

    override fun setValue(thisRef: Any, property: KProperty<*>, value: String?) {
        preferences.edit {
            putString(name, value)
        }
    }
}