eventlisteners.scala

package org.snippets

import scala.collection.mutable.ListBuffer
import scala.reflect.ClassTag


trait Event[T] {
}

trait EventListener[T] {
  def onEvent(event: Event[T])
}

trait Listenable[T] {
  val name: String
  val listeners: ListBuffer[EventListener[T]]
}

object Event {
  var cachedListenables: Map[ClassTag[_], Listenable[_]] = Map()

  implicit def eventIsListenable[T: ClassTag]: Listenable[T] = {
    val typ = implicitly[ClassTag[T]]
    cachedListenables.get(typ) match {
      case None =>
        val newVal = new Listenable[T] {
          override val name: String = s"Listeners of Event[${implicitly[ClassTag[T]]}]"
          override val listeners: ListBuffer[EventListener[T]] = ListBuffer()
        }
        cachedListenables = cachedListenables.updated(typ, newVal)
        newVal
      case Some(l) => l.asInstanceOf[Listenable[T]]
    }
  }
}


object TypedEvents {

  def dispatchEvent[T](event: Event[T])(implicit ev: Listenable[T]): Unit = {
    val listeners = ev.listeners
    println(s"Invoking ${ev.name} , ${ev.hashCode}(相同类型的Event应使用同一个listener集合)")

    listeners.foreach(listener => {
      listener.onEvent(event)
    })
  }


  def main(args: Array[String]): Unit = {
    import Event._
    dispatchEvent(new Event[Int] {})
    dispatchEvent(new Event[Int] {})
    dispatchEvent(new Event[Int] {})
    dispatchEvent(new Event[String] {})
    dispatchEvent(new Event[String] {})
  }
}