Scala 监听器/观察器
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Scala Listener/Observer
提问by Jeb
Typically, in Java, when I've got an object who's providing some sort of notification to other objects, I'll employ the Listener/Observer pattern.
通常，在 Java 中，当我有一个对象向其他对象提供某种通知时，我将使用侦听器/观察者模式。
Is there a more Scala-like way to do this? Should I be using this pattern in Scala, or is there something else baked into the language I should be taking advantage of?
有没有更像 Scala 的方法来做到这一点？我应该在 Scala 中使用这种模式，还是应该在我应该利用的语言中加入其他东西？
回答by Alex Cruise
You can still accumulate a list of callbacks, but you can just make them functions instead of having to come up with yet another single method interface.
您仍然可以累积一个回调列表，但您可以让它们发挥作用，而不必再想出另一个单一的方法接口。
e.g.
例如
case class MyEvent(...)
object Foo {
var listeners: List[MyEvent => ()] = Nil
def listen(listener: MyEvent => ()) {
listeners ::= listener
}
def notify(ev: MyEvent) = for (l <- listeners) l(ev)
}
Also read this this somewhat-related paperif you feel like taking the red pill. :)
如果您想服用红色药丸，也可以阅读这篇与此相关的论文。:)
回答by Alexey Romanov
Is there a more Scala-like way to do this?
有没有更像 Scala 的方法来做到这一点？
Yes. Read the paper Deprecating the Observer Patternby Ingo Maier, Tiark Rompf, and Martin Odersky.
是的。阅读Ingo Maier、Tiark Rompf 和 Martin Odersky的论文Deprecating the Observer Pattern。
Update 27-Apt-2015:There is also a more recent Deprecating the Observer Pattern with Scala.Reactby Maier and Odersky.
2015 年 27 月更新：Maier 和 Odersky还发表了更新的Deprecating the Observer Pattern with Scala.React。
回答by Brian
trait Observer[S] {
def receiveUpdate(subject: S);
}
trait Subject[S] {
this: S =>
private var observers: List[Observer[S]] = Nil
def addObserver(observer: Observer[S]) = observers = observer :: observers
def notifyObservers() = observers.foreach(_.receiveUpdate(this))
}
This snippet is pretty similar to what one would find in Java with some Scala features. This is from Dean Wampler's blog - http://blog.objectmentor.com/articles/2008/08/03/the-seductions-of-scala-part-i
这个片段与在 Java 中发现的具有一些 Scala 特性的片段非常相似。这是来自 Dean Wampler 的博客 - http://blog.objectmentor.com/articles/2008/08/03/the-seductions-of-scala-part-i
This uses some Scala features such as generics as denoted by the [S], traits which are like Java interfaces but more powerful, :: to prepend an observer to the list of observers, and a foreach with the parameter using an _ which evaluates to the current observer.
这使用了一些 Scala 特性，例如由 [S] 表示的泛型、类似于 Java 接口但功能更强大的特性、:: 将观察者添加到观察者列表中，以及带有参数的 foreach 使用 _ 评估为当前的观察者。
回答by IttayD
You can use scala.collection.mutable.Publisher and scala.collection.mutable.Subscriber to create a pub/sub implementation
您可以使用 scala.collection.mutable.Publisher 和 scala.collection.mutable.Subscriber 来创建发布/订阅实现
