今天談一下RxSwift中的組合操作，和RAC一樣?？梢詤⒄誖AC理解。

Combination Operators在RxSwift中的實(shí)現(xiàn)有五種：

• startWith
• merge
• zip
• combineLatest
• switchLatest

StartWith

在Observable釋放元素之前，發(fā)射指定的元素序列

StartWith.png

 let disposeBag = DisposeBag()
        Observable.of(["1","2","3"]).startWith(["0"]).subscribe({ (event) in
            print(event)
        }).disposed(by: disposeBag)

執(zhí)行結(jié)果如下：

next(["0"])
next(["1", "2", "3"])
completed

Merge

將多個(gè)Observable組合成單個(gè)Observable,并且按照時(shí)間順序發(fā)射對(duì)應(yīng)事件

Merge.png

       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("")
        subject2.onNext("??")
        subject1.onNext("")
        subject2.onNext("???")

??

???

zip

將多個(gè)Observable(注意：必須是要成對(duì))組合成單個(gè)Observable，當(dāng)有事件到達(dá)時(shí)，會(huì)在每個(gè)序列中對(duì)應(yīng)的索引上對(duì)應(yīng)的元素發(fā)出。

zip.png

   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

combineLatest.png

當(dāng)一個(gè)項(xiàng)目由兩個(gè)Observables發(fā)射時(shí)，通過一個(gè)指定的功能將每個(gè)Observable觀察到的最新項(xiàng)目組合起來，并根據(jù)該功能的結(jié)果

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")

執(zhí)行結(jié)果：

A--1
A--2
B--2
C--2

switchLatest

切換Observable隊(duì)列

let disposeBag = DisposeBag()

let subject1 = BehaviorSubject(value: "1")
let subject2 = BehaviorSubject(value: "A")

let variable = Variable(subject1)

variable.asObservable()
    .switchLatest()
    .subscribe(onNext: { print($0) })
    .disposed(by: disposeBag)

subject1.onNext("2")
subject1.onNext("3")

variable.value = subject2

subject1.onNext("4")
subject2.onNext("B")

執(zhí)行結(jié)果：

1
2
3
A
B