RxSwift Combining Observables

startWith

在Observable释放元素之前，发射指定的元素序列。

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let disposeBag = DisposeBag()
Observable.of(["C","C++","OC"]).startWith(["先吃饱饭再学习"]).subscribe({ (event) in
  print(event)
}).disposed(by: disposeBag)

"先吃饱饭再学习","C", "C++", "OC"

merge

将多个Observable组合成单个Observable,并且按照时间顺序发射对应事件。

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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")

zip

将多个Observable(注意：必须是要成对)组合成单个Observable，当有事件到达时，会在每个序列中对应的索引上对应的元素发出。(ps:之前版本的RxSwift好像最多只能组合8个Observable)

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let disposeBag = DisposeBag()
let subject1 = PublishSubject<String>()
let subject2 = PublishSubject<String>()

Observable.zip(subject1, subject2) { string1,string2 in
    "\(string1)--\(string2)"
    }.subscribe(onNext: {print($0)}).disposed(by: disposeBag)
    
subject1.onNext("A")
subject1.onNext("B")
subject1.onNext("C")
subject2.onNext("1")
subject2.onNext("2")
// A--1, B--2

combineLatest

当一个项目由两个Observable发射时，通过一个指定的功能将每个Observable观察到的最新项目组合起来，并根据该功能的结果发射事件。

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let disposeBag = DisposeBag()
let subject1 = PublishSubject<String>()
let subject2 = PublishSubject<String>()
    
Observable.combineLatest(subject1, subject2) { string1,string2 in
    "\(string1)--\(string2)"
    }.subscribe(onNext: {print($0)}).disposed(by: disposeBag)
    
subject1.onNext("A")
subject2.onNext("1")
subject2.onNext("2")
subject1.onNext("B")
subject1.onNext("C")
// A--1, A--2, B--2, C--2

switchLatest

切换Observable队列。

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let disposeBag = DisposeBag()
let subject1 = BehaviorSubject(value: "1")
let subject2 = BehaviorSubject(value: "A")
 let variable = BehaviorRelay(value: subject1)
        
variable.asObservable()
        .switchLatest()
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
            
subject1.onNext("2")
subject1.onNext("3")
variable.accept(subject2)
subject1.onNext("4")
subject2.onNext("B")
打印结果：1,2,3,A,B