RxSwift中的组合操作

今天谈一下RxSwift中的组合操作，和RAC一样。可以参照RAC理解。

Combination Operators在RxSwift中的实现有五种：

• startWith
• merge
• zip
• combineLatest
• switchLatest

StartWith

在Observable释放元素之前，发射指定的元素序列

StartWith.png

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

执行结果如下：

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

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

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

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。

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

当一个项目由两个Observables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

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")

执行结果：

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

switchLatest

切换Observable队列

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")

执行结果：

1
2
3
A
B