---

ObjectiveCBridging

RACSignal -> Signal, SignalProducer

RACCommand -> Action

RACScheduler -> SchedulerType

RACDisposable -> Disposable

詳細可以參看ObjectiveCBridging.swift

什麼是ReactiveCocoa

什麼是信號

ReactiveCocoa的冷熱信號

RAC4的 Signal 對應RAC2的 RACSubject，為熱信號，SignalProducer 對應 RACSignal 為冷信號。

熱信號是自動的，就算沒有訂閱者也會即刻推送；冷信號是主動的，有訂閱者才推送

熱信號可以有多個訂閱者，一對多；冷信號只能一對一，當有新的訂閱者，信號是重新完好發送的

抽象的說：熱信號像是直播，冷信號像是點播

熱信號

參看一個例子

// 創立信號
let (signal, observer) = Signal.pipe()
// 監聽器1：立刻監聽
signal.observeResult {
    NSLog("Subscriber 1 get a next value: \($0)")
}
// 監聽器2：0.1s後監聽
QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 0.1)) {
    signal.observeResult({ (result) in
        NSLog("Subscriber 2 get a next value: \(result)")
    })
}
// 發送Next信號：1s後發送"package 1"
QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 1)) { 
    NSLog("Signal send package 1 ...")
    observer.sendNext("package 1")
}
// 監聽器3：1.1s後監聽
QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 1.1)) { 
    signal.observeResult {
        NSLog("Subscriber 3 get a next value: \($0)")
    }
}
// 發送Next信號: 2s後發送"package 2"
QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 2)) { 
    NSLog("signal send package 2 ...")
    observer.sendNext("package 2")
}

運轉：

2016-12-18 19:42:16.206588 TestRAC4[695:389286] start ...
2016-12-18 19:42:17.249072 TestRAC4[695:389286] Signal send package 1 ...
2016-12-18 19:42:17.254583 TestRAC4[695:389286] Subscriber 1 get a next value: .Success(package 1)
2016-12-18 19:42:17.254899 TestRAC4[695:389286] Subscriber 2 get a next value: .Success(package 1)
2016-12-18 19:42:18.393983 TestRAC4[695:389286] signal send package 2 ...
2016-12-18 19:42:18.394386 TestRAC4[695:389286] Subscriber 1 get a next value: .Success(package 2)
2016-12-18 19:42:18.394582 TestRAC4[695:389286] Subscriber 2 get a next value: .Success(package 2)
2016-12-18 19:42:18.394769 TestRAC4[695:389286] Subscriber 3 get a next value: .Success(package 2)

正如之前提到的熱信號的特點，熱信號不關懷能否有人監聽，有發生信號就發送，有人監聽就發個監聽者。0.1s,2s辨別發送next事情，0s,0.1s,1.1s辨別發生一個監聽者，所以第一個信號只要監聽者1，2能收到；第二個next收回時三個監聽器都預備好了，都能收到。

冷信號

再看看冷信號的例子：

let producer = SignalProducer.init { (sink, _) in
    QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 1)) {
        NSLog("Producer send package 1 ...")
        sink.sendNext("package 1")
    }
    QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 2)) {
        NSLog("Producer send package 2 ...")
        sink.sendNext("package 2")
    }
}
QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 2)) {
    NSLog("setup Subsrciber 1")
    producer.startWithResult({ (msg) in
        NSLog("Subscriber 1 get a next value: \(msg)")
    })
}
QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 3)) {
    NSLog("setup Subsrciber 2")
    producer.startWithResult({ (msg) in
        NSLog("Subscriber 2 get a next value: \(msg)")
    })
}

以下是輸入：

2016-12-18 20:05:36.396118 TestRAC4[703:394073] start ...
2016-12-18 20:05:38.600637 TestRAC4[703:394073] setup Subsrciber 1
2016-12-18 20:05:39.681697 TestRAC4[703:394073] setup Subsrciber 2
2016-12-18 20:05:39.682077 TestRAC4[703:394073] Producer send package 1 ...
2016-12-18 20:05:39.685559 TestRAC4[703:394073] Subscriber 1 get a next value: .Success(package 1)
2016-12-18 20:05:40.753463 TestRAC4[703:394073] Producer send package 2 ...
2016-12-18 20:05:40.753865 TestRAC4[703:394073] Subscriber 1 get a next value: .Success(package 2)
2016-12-18 20:05:40.754679 TestRAC4[703:394073] Producer send package 1 ...
2016-12-18 20:05:40.754898 TestRAC4[703:394073] Subscriber 2 get a next value: .Success(package 1)
2016-12-18 20:05:41.881230 TestRAC4[703:394073] Producer send package 2 ...
2016-12-18 20:05:41.881673 TestRAC4[703:394073] Subscriber 2 get a next value: .Success(package 2)

運用冷信號，信號在順序起來第1s,2s辨別發送了一個next。而在2s,3s辨別樹立了一個監聽。第一個監聽樹立後1s,2s辨別收到一個信號。第二信號樹立的1s,2s後也辨別收到了異樣的信號。

冷信號轉化為特殊熱信號

由於冷信號每次訂閱都重新發送事情，故有時分我們需求屢次訂閱時會形成不希望的反復發送（這稱為信號的反作用），我們需求將冷信號轉為具有熱信號特征的冷信號。

參看一個例子，我們用冷，熱信號在0.1s後發送三個next事情，然後如下停止監聽：

// 我們用2個監控來監控generateSignal()發生的信號 #1
let signal = generateSignal()

producer.startWithResult{ NSLog("Subscriber 1 get a next value: \($0)") }

QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 1)) {
    producer.startWithResult{ NSLog("Subscriber 2 get a next value: \($0)") }
}

先看看假如是發生了普通的冷信號：

func generateSignal() -> SignalProducer {
    let producer = SignalProducer.init { (observer, _) in
        QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 1)) {
            NSLog("producer send package 1 ...")
            observer.sendNext("package 1")
            NSLog("producer send package 2 ...")
            observer.sendNext("package 2")
            NSLog("producer send package 3 ...")
            observer.sendNext("package 3")
        }
    }
    return producer
}

輸入如我們所料，信號被反復發送了。

2016-12-18 21:46:21.295670 TestRAC4[742:413995] start ...
2016-12-18 21:46:22.389634 TestRAC4[742:413995] producer send package 1 ...
2016-12-18 21:46:22.397032 TestRAC4[742:413995] Subscriber 1 get a next value: .Success(package 1)
2016-12-18 21:46:22.397397 TestRAC4[742:413995] producer send package 2 ...
2016-12-18 21:46:22.398235 TestRAC4[742:413995] Subscriber 1 get a next value: .Success(package 2)
2016-12-18 21:46:22.398415 TestRAC4[742:413995] producer send package 3 ...
2016-12-18 21:46:22.398608 TestRAC4[742:413995] Subscriber 1 get a next value: .Success(package 3)
2016-12-18 21:46:23.496484 TestRAC4[742:413995] producer send package 1 ...
2016-12-18 21:46:23.496886 TestRAC4[742:413995] Subscriber 2 get a next value: .Success(package 1)
2016-12-18 21:46:23.497061 TestRAC4[742:413995] producer send package 2 ...
2016-12-18 21:46:23.497255 TestRAC4[742:413995] Subscriber 2 get a next value: .Success(package 2)
2016-12-18 21:46:23.497413 TestRAC4[742:413995] producer send package 3 ...
2016-12-18 21:46:23.498869 TestRAC4[742:413995] Subscriber 2 get a next value: .Success(package 3)

假如改成熱信號呢？

func generateSignal() -> Signal {
    let (signal, observer) = Signal.pipe()
    QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 0.1)) {
        NSLog("producer send package 1 ...")
        observer.sendNext("package 1")
        NSLog("producer send package 2 ...")
        observer.sendNext("package 2")
        NSLog("producer send package 3 ...")
        observer.sendNext("package 3")
    }
    return signal
}

let signal = generateSignal()

signal.observeResult { NSLog("Subscriber 1 get a next value: \($0)") }

QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 1)) {
    signal.observeResult{ NSLog("Subscriber 2 get a next value: \($0)") }
}

輸入也如我們所料，只要監聽2能搜到事情，且信號都只發送一次。

2016-12-18 21:54:34.527911 TestRAC4[745:415500] start ...
2016-12-18 21:54:34.634711 TestRAC4[745:415500] producer send package 1 ...
2016-12-18 21:54:34.637899 TestRAC4[745:415500] Subscriber 1 get a next value: .Success(package 1)
2016-12-18 21:54:34.638067 TestRAC4[745:415500] producer send package 2 ...
2016-12-18 21:54:34.638146 TestRAC4[745:415500] Subscriber 1 get a next value: .Success(package 2)
2016-12-18 21:54:34.638195 TestRAC4[745:415500] producer send package 3 ...
2016-12-18 21:54:34.638334 TestRAC4[745:415500] Subscriber 1 get a next value: .Success(package 3)

緩沖 buffer

經過SignalProducer.buffer()創立，是一個事情的隊列（通常指定數量），當新信號發生時，會重新執行隊列裡的事情。和pipe類似，這個辦法前往一個察看者。每個發給這個察看者的事情會被參加隊列。假如這個緩沖區曾經到達創立時預定的數量，當新的事情發來時，最早的一個會被移出隊列。

假如運用buffer來處置呢？我們將下面的冷信號稍作修正：

func generateSignal() -> SignalProducer {
    let (producer, observer) = SignalProducer.buffer(Int.max)
    QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 1)) {
        NSLog("producer send package 1 ...")
        observer.sendNext("package 1")
        NSLog("producer send package 2 ...")
        observer.sendNext("package 2")
        NSLog("producer send package 3 ...")
        observer.sendNext("package 3")
    }
    return producer
}

輸入發現，似乎冷信號變成了熱信號了，只發送了一次。但又具有冷信號的特點：兩個監聽器都能收到事情。

2016-12-18 21:44:29.971493 TestRAC4[740:413482] start ...
2016-12-18 21:44:31.071352 TestRAC4[740:413482] producer send package 1 ...
2016-12-18 21:44:31.075839 TestRAC4[740:413482] Subscriber 1 get a next value: .Success(package 1)
2016-12-18 21:44:31.076115 TestRAC4[740:413482] producer send package 2 ...
2016-12-18 21:44:31.076580 TestRAC4[740:413482] Subscriber 1 get a next value: .Success(package 2)
2016-12-18 21:44:31.076773 TestRAC4[740:413482] producer send package 3 ...
2016-12-18 21:44:31.077035 TestRAC4[740:413482] Subscriber 1 get a next value: .Success(package 3)
2016-12-18 21:44:31.078167 TestRAC4[740:413482] Subscriber 2 get a next value: .Success(package 1)
2016-12-18 21:44:31.078420 TestRAC4[740:413482] Subscriber 2 get a next value: .Success(package 2)
2016-12-18 21:44:31.078771 TestRAC4[740:413482] Subscriber 2 get a next value: .Success(package 3)

buffer(Int.max)這裡的參數表示這個緩沖大小，假如設置為1，那麼訂閱者將只能收到最後一個next事情“package 3”；假如設置為2，只能收到最後兩個next事情“package 2”，“package 3”。

replayLazily

假設我們不能修generateSignal()裡的代碼，這是由第三方提供的，我們可以運用replayLazily。

let producer = generateSignal().replayLazily(Int.max)  // 直接用之前的冷信號

producer.startWithResult { NSLog("Subscriber 1 get a next value: \($0)") }

QueueScheduler.mainQueueScheduler.scheduleAfter(NSDate(timeIntervalSinceNow: 1)) {
    producer.startWithResult { NSLog("subscriber 2 get a next value: \($0)") }
}

輸入如下，和buffer是一樣的效果：

2016-12-18 22:04:48.364076 TestRAC4[753:417953] start ...
2016-12-18 22:04:48.482124 TestRAC4[753:417953] producer send package 1 ...
2016-12-18 22:04:48.484271 TestRAC4[753:417953] Subscriber 1 get a next value: .Success(package 1)
2016-12-18 22:04:48.484422 TestRAC4[753:417953] producer send package 2 ...
2016-12-18 22:04:48.484665 TestRAC4[753:417953] Subscriber 1 get a next value: .Success(package 2)
2016-12-18 22:04:48.484852 TestRAC4[753:417953] producer send package 3 ...
2016-12-18 22:04:48.485120 TestRAC4[753:417953] Subscriber 1 get a next value: .Success(package 3)
2016-12-18 22:04:49.454274 TestRAC4[753:417953] subscriber 2 get a next value: .Success(package 1)
2016-12-18 22:04:49.454659 TestRAC4[753:417953] subscriber 2 get a next value: .Success(package 2)
2016-12-18 22:04:49.454897 TestRAC4[753:417953] subscriber 2 get a next value: .Success(package 3)

那麼replayLazily(Int.max)這個參數和buffer的相反嗎？我們修正成1或2一看就知道。答案是相反

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