Learn to code with RxSwift

• 首先,何为RxSwift?

RxSwift是ReactiveX的Swift版本,一个响应式变成框架。传送门

• 开始之前,先介绍两个function,并没有什么实质性作用,只是为了方便学习演示

/**
 延迟`delay`时长之后执行`closure`闭包
 - parameter delay: 闭包延迟执行时间
 - parameter closure: 返回值`Void`的闭包
 */
public func delay(_ delay: Double, closure: @escaping (Swift.Void) -> Swift.Void)

/**
 起到一个分割线作用
 - parameter description: example 简介
 - parameter action: 返回值`Void`的闭包
 */
public func example(_ description: String, action: (Swift.Void) -> Swift.Void)

• RxSwift基础

Observable: Observable是观察着模式中的被观察对象,相当于一个事件序列GeneratorType,它会向它的订阅者发送事件信息,

• next() :一个新的事件
• complete() :完成事件
• error() : 错误事件

多数情况都是对不同的Observable进行subscribe操作,并在接收到事件后进行相应的操作

---

• 名词解释

• DisposeBag

相当于一个autoreleasepool(自动释放池),对观察者进行管理,在适当的时候销毁观察者

• Observable

Observables will not execute their subscription closure unless there is a subscriber
Observables只有被订阅之后才会被执行,否则不予执行

```

example("一个未被订阅的Observable") {
_ = Observable<String>.create { observerOfString -> Disposable in
print("This will never be printed")
observerOfString.on(.next("😬"))
observerOfString.on(.completed)
return Disposables.create()
}
}
//不会打印任何数据,因为该Observable没有被订阅

- ###### subscribe
> subscribe是订阅`sequence`发出的事件，比如`next`事件，`error`事件等。而`subscribe(onNext:)`是监听`sequence`发出的`next`事件中的`element`进行处理，他会忽略`error`和`completed`事件。相对应的还有`subscribe(onError:) `和 `subscribe(onCompleted:)`

   ```
example("被订阅的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)
}
执行结果:
--- 被订阅的Observable ---
Observable created
next(😉)
completed

---

• Creating and Subscribing to Observables/ 创建并订阅Observables

• never 创建一个空序列,不发送任何事件

example("never") {
    let disposeBag = DisposeBag()
    let neverSequence = Observable<String>.never()
    neverSequence
        .subscribe { _ in
            print("This will never be printed")
    }
    .addDisposableTo(disposeBag)
}

• empty 一个空的序列，它只发送 .Completed 消息

example("empty") {
    let disposeBag = DisposeBag()
        Observable<Int>.empty()
        .subscribe { event in
            print(event)
        }
        .disposed(by: disposeBag)
}
//执行结果:
--- empty example ---
completed

• just 只包含一个元素的序列,发送一个next事件和completed事件

    example("just") {
    let disposeBag = DisposeBag()
    Observable.just("🔴")
        .subscribe { event in
            print(event)
        }
        .disposed(by: disposeBag)
}
//执行结果:
--- just example ---
next(🔴)
completed

• of 将所有元素依次转换为序列发送

example("of") {
    let disposeBag = DisposeBag()
    Observable.of("🐶", "🐱", "🐭", "🐹")
        .subscribe(onNext: { element in
            print(element)
        })
        .disposed(by: disposeBag)
}
//执行结果
--- of example ---
🐶
🐱
🐭
🐹

• from 从数组或字典或集合的所有元素创建序列发送

example("from") {
    let disposeBag = DisposeBag()
        Observable.from(["🐶", "🐱", "🐭", "🐹"])
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}
//执行结果
--- from example ---
🐶
🐱
🐭
🐹

• create 创建一个自定义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)
}
//执行结果:
--- create example ---
next(🔴)
completed

• error 创建一个只发送error事件的Observable

example("error") {
    let disposeBag = DisposeBag()
    Observable<Int>.error(TestError.test)
        .subscribe { print($0) }
        .disposed(by: disposeBag)
}
//执行结果:
--- error example ---
error(test)

---

• Subject

Subject可以订阅别的Observable,也可以被订阅并给它的订阅者发送事件
常用:

1. PublishSubject
2. ReplaySubject
3. BehaviorSubject
4. Variable

• PublishSubject 它的订阅者只能接收到订阅后发送的事件,无法接收到订阅之前的事件

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("🅱️")
}
//执行结果:
--- 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 它的订阅者定接收到订阅之后发出的事件,并且能接收到订阅之前的信号,至于能接收到订阅之前的多少个信号则由 bufferSize 参数决定

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("🅱️")
}
//执行结果:
--- 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 它的订阅者定接收到订阅之后发出的事件,并且能接收到订阅之前的前一个信号

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("🍊")
}
//执行结果:
--- 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 它的订阅者定接收到订阅之后发出的事件和订阅之前的前一个信号,并且当它的 value 发生改变时所有的订阅者能收到事件,完成后向所有订阅者发送 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 = "🅱️"
}
//执行结果:
--- 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

---

• 组合操作

• startWith 这个不好描述,看代码,别说话,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)
}
//执行结果:
--- startWith example ---
3
🅰️
🅱️
2
1
🐶
🐱
🐭
🐹

• merge 把两个队列按照顺序组合在一起

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")
}
//执行结果:
--- merge example ---
🅰️
🅱️
①
②
🆎
③

• zip 将多个序列组合在一起,当所有序列能凑成一组(一一对应)时才发送事件

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)
}
//执行结果:
--- zip example ---
🅰️ 1
🅱️ 2
🆎 3

• combineLatest 多个序列合并,每个序列的最新值进行组合

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("🆎")
}
//执行结果:
--- combineLatest example ---
🅱️ 1
🅱️ 2
🆎 2

---

• 转换操作

• map 对序列的值做转换操作后返回,序列的值发生改变

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)
}
//执行结果:
--- map example ---
1
4
9

• flatMap and flatMapLatest 看代码

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
}
//执行结果:
--- flatMap and flatMapLatest example ---
80
85
90
95
100