可連接的可觀察序列類似于普通觀察到的序列，但他們不會開始在訂閱以后發(fā)出事件，但是，只有當他們調(diào)用connect()方法。這樣，你可以讓所有需要等待并且想要訂閱的觀察者訂閱一個可連接的可觀察序列。
在學習可連接的Observable時，先來看一下普通的序列

let interval = Observable<Int>.interval(1, scheduler: MainScheduler.instance)
// 每隔一秒就調(diào)用一次的Observable
_ = interval
    .subscribe(onNext: { print("Subscription: 1, Event: \($0)") })

delay(5) {                     //  必須手動添加延遲才能訂閱
    _ = interval
        .subscribe(onNext: { print("Subscription: 2, Event: \($0)") })
}

func delay(_ interval: TimeInterval, closure:@escaping () ->Void) {
        let delay = DispatchTime.now() + interval   // swift 版本的dispatch
        DispatchQueue.main.asyncAfter(deadline: delay, execute: closure)
    }

publish

將一個源觀測序列轉(zhuǎn)換為一個可連接序列。

let intSequence = Observable<Int>.interval(1, scheduler: MainScheduler.instance)
    .publish()

_ = intSequence
    .subscribe(onNext: { print("Subscription 1:, Event: \($0)") })

delay(2) { _ = intSequence.connect() }     // 觸發(fā)

delay(4) {
    _ = intSequence
        .subscribe(onNext: { print("Subscription 2:, Event: \($0)") })
}

delay(6) {
    _ = intSequence
        .subscribe(onNext: { print("Subscription 3:, Event: \($0)") })
}

replay

將一個源觀測序列轉(zhuǎn)換為一個可連接序列，并將給新的訂閱者發(fā)送特點數(shù)量的之前的事件

let intSequence = Observable<Int>.interval(1, scheduler: MainScheduler.instance)
    .replay(5)

_ = intSequence
    .subscribe(onNext: { print("Subscription 1:, Event: \($0)") })

delay(2) { _ = intSequence.connect() }

delay(4) {
    _ = intSequence
        .subscribe(onNext: { print("Subscription 2:, Event: \($0)") })
}

delay(8) {
    _ = intSequence
        .subscribe(onNext: { print("Subscription 3:, Event: \($0)") })
}      // 彌補之前publish的不足

multicast

將一個源觀測序列轉(zhuǎn)換為一個可連接序列,并通過指定的subject發(fā)出。

let subject = PublishSubject<Int>()

    _ = subject
        .subscribe(onNext: { print("Subject: \($0)") })

    let intSequence = Observable<Int>.interval(1, scheduler: MainScheduler.instance)
        .multicast(subject)

    _ = intSequence
        .subscribe(onNext: { print("\tSubscription 1:, Event: \($0)") })

    delay(2) { _ = intSequence.connect() }

    delay(4) {
        _ = intSequence
            .subscribe(onNext: { print("\tSubscription 2:, Event: \($0)") })
    }

    delay(6) {
        _ = intSequence
            .subscribe(onNext: { print("\tSubscription 3:, Event: \($0)") })
    }
/*  
    Subject: 0
          Subscription 1:, Event: 0
    Subject: 1
      Subscription 1:, Event: 1
      Subscription 2:, Event: 1
    Subject: 2
      Subscription 1:, Event: 2
      Subscription 2:, Event: 2
*/

錯誤處理操作