DelegatedPreference.kt

class DelegatedPreference<T>(val context: Context, val default: T) : ReadWriteProperty<Any, T> {

  override fun getValue(thisRef: Any, property: KProperty<*>): T {
    return context.defaultSharedPreferences.run {
      when (default) {
        is String  -> getString(property.name, default)
        is Long    -> getLong(property.name, default)
        is Int     -> getInt(property.name, default)
        is Boolean -> getBoolean(property.name, default)
        else       -> null
      } as T
    }
  }

  override fun setValue(thisRef: Any, property: KProperty<*>, value: T) {
    context.defaultSharedPreferences.edit().apply {
      when (value) {
        is String  -> putString(property.name, value)
        is Long    -> putLong(property.name, value)
        is Int     -> putInt(property.name, value)
        is Boolean -> putBoolean(property.name, value)
      }
    }.apply()
  }
}

Example.kt

class MainActivity : BaseActivity() {
  
  // ...
  
  private var pref_is_enabled by DelegatedPreference(this /** Context **/ , false)
  
  private fun onSwitchClicked(value : Boolean) {
    pref_is_enabled = value // Save ["pref_is_enabled" : $value] preference automatically
    ui.switch.isChecked = pref_is_enabled // Fetch "pref_is_enabled" preference value automatically
  }
  
}