Learn to code with RxSwift

  • 首先,何為RxSwift?

RxSwift是ReactiveX的Swift版本,一個(gè)響應(yīng)式變成框架。傳送門

  • 開始之前,先介紹兩個(gè)function,并沒有什么實(shí)質(zhì)性作用,只是為了方便學(xué)習(xí)演示

/**
 延遲`delay`時(shí)長之后執(zhí)行`closure`閉包
 - parameter delay: 閉包延遲執(zhí)行時(shí)間
 - parameter closure: 返回值`Void`的閉包
 */
public func delay(_ delay: Double, closure: @escaping (Swift.Void) -> Swift.Void)

/**
 起到一個(gè)分割線作用
 - parameter description: example 簡介
 - parameter action: 返回值`Void`的閉包
 */
public func example(_ description: String, action: (Swift.Void) -> Swift.Void)

  • RxSwift基礎(chǔ)

Observable: Observable是觀察著模式中的被觀察對象,相當(dāng)于一個(gè)事件序列GeneratorType,它會向它的訂閱者發(fā)送事件信息,

  • next() :一個(gè)新的事件
  • complete() :完成事件
  • error() : 錯(cuò)誤事件

多數(shù)情況都是對不同的Observable進(jìn)行subscribe操作,并在接收到事件后進(jìn)行相應(yīng)的操作

  • 名詞解釋

  • DisposeBag

相當(dāng)于一個(gè)autoreleasepool(自動釋放池),對觀察者進(jìn)行管理,在適當(dāng)?shù)臅r(shí)候銷毀觀察者

  • Observable

Observables will not execute their subscription closure unless there is a subscriber
Observables只有被訂閱之后才會被執(zhí)行,否則不予執(zhí)行

```

example("一個(gè)未被訂閱的Observable") {
_ = Observable<String>.create { observerOfString -> Disposable in
print("This will never be printed")
observerOfString.on(.next("??"))
observerOfString.on(.completed)
return Disposables.create()
}
}
//不會打印任何數(shù)據(jù),因?yàn)樵揙bservable沒有被訂閱

- ###### subscribe
> subscribe是訂閱`sequence`發(fā)出的事件，比如`next`事件，`error`事件等。而`subscribe(onNext:)`是監(jiān)聽`sequence`發(fā)出的`next`事件中的`element`進(jìn)行處理，他會忽略`error`和`completed`事件。相對應(yīng)的還有`subscribe(onError:) `和 `subscribe(onCompleted:)`

   ```
example("被訂閱的Observable") {
     let disposeBag = DisposeBag()
     Observable<String>.create { observerOfString in
       print("Observable created")
       observerOfString.on(.next("??"))
       observerOfString.on(.completed)
       return Disposables.create()
       }
       .subscribe { event in
           print(event)
       }.addDisposableTo(disposeBag)
}
執(zhí)行結(jié)果:
--- 被訂閱的Observable ---
Observable created
next(??)
completed

  • Creating and Subscribing to Observables/ 創(chuàng)建并訂閱Observables

  • never 創(chuàng)建一個(gè)空序列,不發(fā)送任何事件 
example("never") {
    let disposeBag = DisposeBag()
    let neverSequence = Observable<String>.never()
    neverSequence
        .subscribe { _ in
            print("This will never be printed")
    }
    .addDisposableTo(disposeBag)
}
  • empty 一個(gè)空的序列，它只發(fā)送 .Completed 消息 
example("empty") {
    let disposeBag = DisposeBag()
        Observable<Int>.empty()
        .subscribe { event in
            print(event)
        }
        .disposed(by: disposeBag)
}
//執(zhí)行結(jié)果:
--- empty example ---
completed
  • just 只包含一個(gè)元素的序列,發(fā)送一個(gè)next事件和completed事件 
    example("just") {
    let disposeBag = DisposeBag()
    Observable.just("??")
        .subscribe { event in
            print(event)
        }
        .disposed(by: disposeBag)
}
//執(zhí)行結(jié)果:
--- just example ---
next(??)
completed
  • of 將所有元素依次轉(zhuǎn)換為序列發(fā)送 
example("of") {
    let disposeBag = DisposeBag()
    Observable.of("??", "??", "??", "??")
        .subscribe(onNext: { element in
            print(element)
        })
        .disposed(by: disposeBag)
}
//執(zhí)行結(jié)果
--- of example ---
??
??
??
??
  • from 從數(shù)組或字典或集合的所有元素創(chuàng)建序列發(fā)送 
example("from") {
    let disposeBag = DisposeBag()
        Observable.from(["??", "??", "??", "??"])
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}
//執(zhí)行結(jié)果
--- from example ---
??
??
??
??
  • create 創(chuàng)建一個(gè)自定義Observable 
example("create") {
    let disposeBag = DisposeBag()
    
    let myJust = { (element: String) -> Observable<String> in
        return Observable.create { observer in
            observer.on(.next(element))
            observer.on(.completed)
            return Disposables.create()
        }
    }
    myJust("??")
        .subscribe { print($0) }
        .disposed(by: disposeBag)
}
//執(zhí)行結(jié)果:
--- create example ---
next(??)
completed
  • error 創(chuàng)建一個(gè)只發(fā)送error事件的Observable 
example("error") {
    let disposeBag = DisposeBag()
    Observable<Int>.error(TestError.test)
        .subscribe { print($0) }
        .disposed(by: disposeBag)
}
//執(zhí)行結(jié)果:
--- error example ---
error(test)

  • Subject

Subject可以訂閱別的Observable,也可以被訂閱并給它的訂閱者發(fā)送事件
常用:

  1. PublishSubject
  2. ReplaySubject
  3. BehaviorSubject
  4. Variable
  • PublishSubject 它的訂閱者只能接收到訂閱后發(fā)送的事件,無法接收到訂閱之前的事件 
example("PublishSubject") {
      let disposeBag = DisposeBag()
      let subject = PublishSubject<String>()
      subject.addObserver("1").disposed(by: disposeBag)
      subject.onNext("??")
      subject.onNext("??")
      subject.addObserver("2").disposed(by: disposeBag)
      subject.onNext("???")
      subject.onNext("???")
}
//執(zhí)行結(jié)果:
--- PublishSubject example ---
Subscription: 1 Event: next(??)
Subscription: 1 Event: next(??)
Subscription: 1 Event: next(???)
Subscription: 2 Event: next(???)
Subscription: 1 Event: next(???)
Subscription: 2 Event: next(???)
  • ReplaySubject 它的訂閱者定接收到訂閱之后發(fā)出的事件,并且能接收到訂閱之前的信號,至于能接收到訂閱之前的多少個(gè)信號則由 bufferSize 參數(shù)決定 
example("ReplaySubject") {
      let disposeBag = DisposeBag()
      let subject = ReplaySubject<String>.create(bufferSize: 1)
      subject.addObserver("1").disposed(by: disposeBag)
      subject.onNext("??")
      subject.onNext("??")
      subject.addObserver("2").disposed(by: disposeBag)
      subject.onNext("???")
      subject.onNext("???")
}
//執(zhí)行結(jié)果:
--- ReplaySubject example ---
Subscription: 1 Event: next(??)
Subscription: 1 Event: next(??)
Subscription: 2 Event: next(??)
Subscription: 1 Event: next(???)
Subscription: 2 Event: next(???)
Subscription: 1 Event: next(???)
Subscription: 2 Event: next(???)
  • BehaviorSubject 它的訂閱者定接收到訂閱之后發(fā)出的事件,并且能接收到訂閱之前的前一個(gè)信號 
example("BehaviorSubject") {
      let disposeBag = DisposeBag()
      let subject = BehaviorSubject(value: "??")
      subject.addObserver("1").disposed(by: disposeBag)
      subject.onNext("??")
      subject.onNext("??")
      subject.addObserver("2").disposed(by: disposeBag)
      subject.onNext("???")
      subject.onNext("???")
      subject.addObserver("3").disposed(by: disposeBag)
      subject.onNext("??")
      subject.onNext("??")
}
//執(zhí)行結(jié)果:
--- BehaviorSubject example ---
Subscription: 1 Event: next(??)
Subscription: 1 Event: next(??)
Subscription: 1 Event: next(??)
Subscription: 2 Event: next(??)
Subscription: 1 Event: next(???)
Subscription: 2 Event: next(???)
Subscription: 1 Event: next(???)
Subscription: 2 Event: next(???)
Subscription: 3 Event: next(???)
Subscription: 1 Event: next(??)
Subscription: 2 Event: next(??)
Subscription: 3 Event: next(??)
Subscription: 1 Event: next(??)
Subscription: 2 Event: next(??)
Subscription: 3 Event: next(??)
  • Variable 它的訂閱者定接收到訂閱之后發(fā)出的事件和訂閱之前的前一個(gè)信號,并且當(dāng)它的 value 發(fā)生改變時(shí)所有的訂閱者能收到事件,完成后向所有訂閱者發(fā)送 complete 事件 
example("Variable") {
      let disposeBag = DisposeBag()
      let variable = Variable("??")
      variable.asObservable().addObserver("1").disposed(by: disposeBag)
      variable.value = "??"
      variable.value = "??"
      variable.asObservable().addObserver("2").disposed(by: disposeBag)
      variable.value = "???"
      variable.value = "???"
}
//執(zhí)行結(jié)果:
--- Variable example ---
Subscription: 1 Event: next(??)
Subscription: 1 Event: next(??)
Subscription: 1 Event: next(??)
Subscription: 2 Event: next(??)
Subscription: 1 Event: next(???)
Subscription: 2 Event: next(???)
Subscription: 1 Event: next(???)
Subscription: 2 Event: next(???)
Subscription: 1 Event: completed
Subscription: 2 Event: completed

  • 組合操作

  • startWith 這個(gè)不好描述,看代碼,別說話,用心去感受 
example("startWith") {
    let disposeBag = DisposeBag()
    Observable.of("??", "??", "??", "??")
        .startWith("1")
        .startWith("2")
        .startWith("3", "???", "???")
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}
//執(zhí)行結(jié)果:
--- startWith example ---
3
???
???
2
1
??
??
??
??
  • merge 把兩個(gè)隊(duì)列按照順序組合在一起 
example("merge") {
      let disposeBag = DisposeBag()
      let subject1 = PublishSubject<String>()
      let subject2 = PublishSubject<String>()
      Observable.of(subject1, subject2)
          .merge()
          .subscribe(onNext: { print($0) })
          .disposed(by: disposeBag)
      subject1.onNext("???")
      subject1.onNext("???")
      subject2.onNext("①")
      subject2.onNext("②")
      subject1.onNext("??")
      subject2.onNext("③")
}
//執(zhí)行結(jié)果:
--- merge example ---
???
???
①
②
??
③
  • zip 將多個(gè)序列組合在一起,當(dāng)所有序列能湊成一組(一一對應(yīng))時(shí)才發(fā)送事件 
example("zip") {
      let disposeBag = DisposeBag()
      let stringSubject = PublishSubject<String>()
      let intSubject = PublishSubject<Int>()
      Observable.zip(stringSubject, intSubject) { stringElement, intElement in
          "\(stringElement) \(intElement)"
          }
          .subscribe(onNext: { print($0) })
          .disposed(by: disposeBag)
      stringSubject.onNext("???")
      stringSubject.onNext("???")
      intSubject.onNext(1)
      intSubject.onNext(2)
      stringSubject.onNext("??")
      intSubject.onNext(3)
}
//執(zhí)行結(jié)果:
--- zip example ---
??? 1
??? 2
?? 3
  • combineLatest 多個(gè)序列合并,每個(gè)序列的最新值進(jìn)行組合 
example("combineLatest") {
      let disposeBag = DisposeBag()
      let stringSubject = PublishSubject<String>()
      let intSubject = PublishSubject<Int>()
      Observable.combineLatest(stringSubject, intSubject) { stringElement, intElement in
              "\(stringElement) \(intElement)"
          }
          .subscribe(onNext: { print($0) })
          .disposed(by: disposeBag)
      stringSubject.onNext("???")
      stringSubject.onNext("???")
      intSubject.onNext(1)
      intSubject.onNext(2)
      stringSubject.onNext("??")
}
//執(zhí)行結(jié)果:
--- combineLatest example ---
??? 1
??? 2
?? 2

  • 轉(zhuǎn)換操作

  • map 對序列的值做轉(zhuǎn)換操作后返回,序列的值發(fā)生改變 
example("map") {
      let disposeBag = DisposeBag()
      Observable.of(1, 2, 3)
          .map { $0 * $0 }   //1*1 2*2 3*3
          .subscribe(onNext: { print($0) })
          .disposed(by: disposeBag)
}
//執(zhí)行結(jié)果:
--- map example ---
1
4
9
  • flatMap and flatMapLatest 看代碼 
example("flatMap and flatMapLatest") {
    let disposeBag = DisposeBag()
    struct Player {
        var score: Variable<Int>
    }
    let ???? = Player(score: Variable(80))
    let ???? = Player(score: Variable(90))
    let player = Variable(????)
    player.asObservable()
        .flatMap { $0.score.asObservable() } // Change flatMap to flatMapLatest and observe change in printed output
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
    ????.score.value = 85
    player.value = ????
    ????.score.value = 95 // Will be printed when using flatMap, but will not be printed when using flatMapLatest
    ????.score.value = 100
}
//執(zhí)行結(jié)果:
--- flatMap and flatMapLatest example ---
80
85
90
95
100
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