觀察者模式

問(wèn)題

當(dāng)一個(gè)事件發(fā)生時(shí)你不得不向一些對(duì)象發(fā)布公告。

解決方案

使用觀察者模式（Observer Pattern）。

class PostOffice
    constructor: () ->
        @subscribers = []
    notifyNewItemReleased: (item) ->
        subscriber.callback(item) for subscriber in @subscribers when subscriber.item is item
    subscribe: (to, onNewItemReleased) ->
        @subscribers.push {'item':to, 'callback':onNewItemReleased}

class MagazineSubscriber
    onNewMagazine: (item) ->
        alert "I've got new "+item

class NewspaperSubscriber
    onNewNewspaper: (item) ->
        alert "I've got new "+item

postOffice = new PostOffice()
sub1 = new MagazineSubscriber()
sub2 = new NewspaperSubscriber()
postOffice.subscribe "Mens Health", sub1.onNewMagazine
postOffice.subscribe "Times", sub2.onNewNewspaper
postOffice.notifyNewItemReleased "Times"
postOffice.notifyNewItemReleased "Mens Health"

討論

這里你有一個(gè)觀察者對(duì)象（PostOffice）和可觀察對(duì)象（MagazineSubscriber, NewspaperSubscriber）。為了通報(bào)發(fā)布新的周期性可觀察對(duì)象的事件，應(yīng)該對(duì) PostOffice進(jìn)行訂閱。每一個(gè)被訂閱的對(duì)象都存儲(chǔ)在PostOffice的內(nèi)部訂閱數(shù)組中。當(dāng)新的實(shí)體周期發(fā)布時(shí)每一個(gè)訂閱者都會(huì)收到通知。