RxSwift (二) Working with Subjects

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首先在playground 中给ObervableType增加一个扩展。方便查看子类订阅时发生的变化

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extension ObservableType{
    ///给每一个观察者增加一个id。并打印id和发射的事件
    func addObservable(_ id:String) -> Disposable {
        
        return subscribe{
        
            print("Subscription:", id, "Event:", $0)
        }
    }
}
func writeSequenceToConsole<O: ObservableType>(name: String, sequence: O) -> Disposable {
    return sequence.subscribe { event in
        print("Subscription: \(name), event: \(event)")
    }
}

PublishSubject

PublishSubject只会把在订阅发生的时间点之后来自原始Observable的数据发射给观察者。

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exampleOf(description: "PublishSubject") { 
    
    let disposeBag = DisposeBag()
    
    let publishSubject = PublishSubject<String>()
    
    ///第一组
    publishSubject.addObservable("no.1").disposed(by: disposeBag)
    
    publishSubject.onNext("2")
    
    publishSubject.onNext("3")
    
    //第二组
    publishSubject.addObservable("no.2").disposed(by: disposeBag)
    
    publishSubject.onNext("🐱")
    
    publishSubject.onNext("🐶")
}

打印结果如下

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------exampleOf:PublishSubject------
Subscription: no.1 Event: next(2)
Subscription: no.1 Event: next(3)
Subscription: no.1 Event: next(🐱)
Subscription: no.2 Event: next(🐱)
Subscription: no.1 Event: next(🐶)
Subscription: no.2 Event: next(🐶)

可以看no.2 并没有收到no.2订阅之前发送的信号（2和3）。

ReplaySubject

ReplaySubject会发射所有来自原始Observable的数据给观察者，无论它们是何时订阅的。也 有其它版本的ReplaySubject，在重放缓存增长到一定大小的时候或过了一段时间后会丢弃旧 的数据(原始Observable发射的)。

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exampleOf(description: "replaySubject") { 
    
    let disposeBag = DisposeBag()
    
    let replaySubject = ReplaySubject<String>.create(bufferSize: 2)
    
    replaySubject.addObservable("no.1").disposed(by: disposeBag)
    
    replaySubject.onNext("第一个事件")
    
    replaySubject.onNext("第二个事件")
    
    
    replaySubject.addObservable("no.2").disposed(by: disposeBag)
    
    replaySubject.onNext("3")
    
    replaySubject.onNext("4")
    
}

打印结果如下

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------exampleOf:replaySubject------
Subscription: no.1 Event: next(第一个事件)
Subscription: no.1 Event: next(第二个事件)
Subscription: no.2 Event: next(第一个事件)
Subscription: no.2 Event: next(第二个事件)
Subscription: no.1 Event: next(3)
Subscription: no.2 Event: next(3)
Subscription: no.1 Event: next(4)
Subscription: no.2 Event: next(4)

会将订阅之前的信号发给新订阅者。如果指定了buttersize,会根据buttersize（我理解为多少个）发送之前的数据

BehaviorSubject

当观察者订阅BehaviorSubject时，它开始发射原始Observable最近发射的数据(如果此时还 没有收到任何数据，它会发射一个默认值)，然后继续发射其它任何来自原始Observable的 数据。

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exampleOf(description: "BehaviorSubject") { 
    
    let disposeBag = DisposeBag()
    
    let subject = BehaviorSubject(value: "behavior")
    
    subject.addObservable("第一个响应").disposed(by: disposeBag)
    
    subject.onNext("第一个事件")
    
    subject.onNext("第二个事件")
    
    subject.addObservable("第二个响应").disposed(by: disposeBag)
    
    subject.onNext("第三个事件")
    
    subject.onNext("第四个事件")
}

打印结果

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------exampleOf:BehaviorSubject------
Subscription: 第一个响应 Event: next(behavior)
Subscription: 第一个响应 Event: next(第一个事件)
Subscription: 第一个响应 Event: next(第二个事件)
Subscription: 第二个响应 Event: next(第二个事件)
Subscription: 第一个响应 Event: next(第三个事件)
Subscription: 第二个响应 Event: next(第三个事件)
Subscription: 第一个响应 Event: next(第四个事件)
Subscription: 第二个响应 Event: next(第四个事件)

Variable

Variable是BehaviorSubject的一层封装。特点不会被显式终结。即：不会收到 .Completed 和 .Error 这类的终结事件，它会主动在析构的时候发送 .Complete 。

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exampleOf(description: "Variable") { 
    
    let disposeBag = DisposeBag()
    
    let variable = Variable<String>("默认值")
    
    variable.asObservable().addObservable("no.1").disposed(by: disposeBag)
    
    variable.value = "第二个值"
    
    variable.value = "第三个值"
    
    variable.asObservable().addObservable("no.2").disposed(by: disposeBag)
    
    variable.value = "第四个值"
    
    variable.value = "第五个值"
}

打印结果

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------exampleOf:Variable------
Subscription: no.1 Event: next(默认值)
Subscription: no.1 Event: next(第二个值)
Subscription: no.1 Event: next(第三个值)
Subscription: no.2 Event: next(第三个值)
Subscription: no.1 Event: next(第四个值)
Subscription: no.2 Event: next(第四个值)
Subscription: no.1 Event: next(第五个值)
Subscription: no.2 Event: next(第五个值)
Subscription: no.1 Event: completed
Subscription: no.2 Event: completed