Controller Argument Delegation. An extensible mechanism for seriaizing values to the Controllers bundle.

ControllerArgumentDelegate.kt

/**
 * An abstract argument delegate that uses the property to infer the key name for the bundle.
 */
abstract class ControllerArgumentDelegate<T : Any> : ReadWriteProperty<Controller, T> {

  private var value: T? = null

  override final fun getValue(thisRef: Controller, property: KProperty<*>): T {
    if (value == null) {
      val key = property.name
      value = fromBundle(thisRef.args, key)
    }
    return value ?: throw IllegalStateException("Property ${property.name} could not be read")
  }

  override final fun setValue(thisRef: Controller, property: KProperty<*>, value: T) {
    val bundle = thisRef.args
    val key = property.name
    toBundle(bundle, key, value)
  }

  abstract fun toBundle(bundle: Bundle, key: String, value: T)
  abstract fun fromBundle(bundle: Bundle, key: String): T
}

EnumArgumentDelegate.kt

class EnumArgumentDelegate<E : Enum<E>>(private val clazz: Class<E>) : ControllerArgumentDelegate<E>() {

  override fun toBundle(bundle: Bundle, key: String, value: E) {
    bundle.putString(key, value.name)
  }

  override fun fromBundle(bundle: Bundle, key: String): E {
    val stringValue = bundle.getString(key)
    return java.lang.Enum.valueOf(clazz, stringValue)
  }
}

inline fun <reified E : Enum<E>> enumArgumentDelegate() = EnumArgumentDelegate(E::class.java)

StringArgumentDelegate.kt

class StringArgumentDelegate : ControllerArgumentDelegate<String>() {

  override fun toBundle(bundle: Bundle, key: String, value: String) {
    bundle.putString(key, value)
  }

  override fun fromBundle(bundle: Bundle, key: String): String = bundle.getString(key)
}

Sample:

class Sample() : Controller() {

  private var heightUnit: HeightUnit by enumArgumentDelegate()
  private var name by StringArgumentDelegate()

  constructor(heightUnit: HeightUnit, name: String) : this() {
    this.heightUnit = heightUnit
    this.name = name
  }

  override fun onCreateView(inflater: LayoutInflater, container: ViewGroup) = TextView(activity!!)
}