Swift - RxSwift: Subject와 Relay

ReactiveX Subject 문서 참고

Subject는 Observer && Observable

• Observer
  • 하나 이상의 Observable을 구독할 수 있음
  • 원래 Cold Observable를 Hot Observable로 변경하는 효과 보임
  • Hot & Cold
• Observable
  • event emit 가능

PublishSubject

• subscribe했을 때 이벤트
  • 값이 업데이트될 때마다
  • 에러
  • subject가 종료 되었을 때

            let publishSubject = PublishSubject<Int>()
      
            let subscribe1 = publishSubject
                .subscribe(onNext: { (num) in
                    print("subscribe1 :", num)
                }, onError: { (error) in
                    print("subscribe1 Erorr: ", error)
                }, onCompleted: {
                    print("subscribe1 onCompleted")
                })
      
            publishSubject.onNext(1)
            publishSubject.onNext(2)
      
            let subscribe2 = publishSubject
                .subscribe(onNext: { (num) in
                    print("subscribe2 :", num)
                }, onError: { (error) in
                    print("subscribe2 Erorr: ", error)
                }, onCompleted: {
                    print("subscribe2 onCompleted")
                })
      
            publishSubject.onNext(3)
      
            publishSubject.onCompleted() // 종료
      
            publishSubject.onNext(4)
            publishSubject.onNext(5)
  

     subscribe1 : 1
     subscribe1 : 2
     subscribe1 : 3
     subscribe2 : 3
     subscribe1 onCompleted
     subscribe2 onCompleted
  

BehaviorSubject: 초기값이 있는 PublishSubject

• 처음 subscribe하면 초기값 또는 직전의 값 들고 옴

            let behaviorSubject = BehaviorSubject<Int>(value: 0)
      
            let subscribe1 = behaviorSubject
                .subscribe(onNext: { (num) in
                    print("subscribe1 :", num)
                }, onError: { (error) in
                    print("subscribe1 Erorr: ", error)
                }, onCompleted: {
                    print("subscribe1 onCompleted")
                })
      
            behaviorSubject.onNext(1)
            behaviorSubject.onNext(2)
      
            let subscribe2 = behaviorSubject
                .subscribe(onNext: { (num) in
                    print("subscribe2 :", num)
                }, onError: { (error) in
                    print("subscribe2 Erorr: ", error)
                }, onCompleted: {
                    print("subscribe2 onCompleted")
                })
      
            behaviorSubject.onNext(3)
      
            behaviorSubject.onCompleted() // 종료
      
            behaviorSubject.onNext(4)
            behaviorSubject.onNext(5)
  

    subscribe1 : 0 // 초기값 0
    subscribe1 : 1
    subscribe1 : 2
    subscribe2 : 2 // 직전 값 2
    subscribe1 : 3
    subscribe2 : 3
    subscribe1 onCompleted
    subscribe2 onCompleted
  

ReplaySubject

• bufferSize만큼 저장해 두었다가, subscribe하면 저장해 둔 최신 값들 반환

            let replaySubject = ReplaySubject<Int>.create(bufferSize: 3)
            // 모든 이벤트 저장: .createUnbounded()
      
            let subscribe1 = replaySubject
                .subscribe(onNext: { (num) in
                    print("subscribe1 :", num)
                }, onError: { (error) in
                    print("subscribe1 Erorr: ", error)
                }, onCompleted: {
                    print("subscribe1 onCompleted")
                })
      
            replaySubject.onNext(1)
            replaySubject.onNext(2)
      
            let subscribe2 = replaySubject
                .subscribe(onNext: { (num) in
                    print("subscribe2 :", num)
                }, onError: { (error) in
                    print("subscribe2 Erorr: ", error)
                }, onCompleted: {
                    print("subscribe2 onCompleted")
                })
      
            replaySubject.onNext(3)
      
            replaySubject.onCompleted() // 종료
      
            replaySubject.onNext(4)
            replaySubject.onNext(5)
  

    subscribe1 : 1
    subscribe1 : 2
    subscribe2 : 1 // 버퍼에 있던 최신값 1
    subscribe2 : 2 // 버퍼에 있던 최신값 2
    subscribe1 : 3
    subscribe2 : 3
    subscribe1 onCompleted
    subscribe2 onCompleted
  

AsyncSubject

• complete가 되면 이벤트 발생 후 종료

            let asyncSubject = AsyncSubject<Int>()
      
            let subscribe1 = asyncSubject
                .subscribe(onNext: { (num) in
                    print("subscribe1 :", num)
                }, onError: { (error) in
                    print("subscribe1 Erorr: ", error)
                }, onCompleted: {
                    print("subscribe1 onCompleted")
                })
      
            asyncSubject.onNext(1)
            asyncSubject.onNext(2)
      
            let subscribe2 = asyncSubject
                .subscribe(onNext: { (num) in
                    print("subscribe2 :", num)
                }, onError: { (error) in
                    print("subscribe2 Erorr: ", error)
                }, onCompleted: {
                    print("subscribe2 onCompleted")
                })
      
            asyncSubject.onNext(3)
      
            asyncSubject.onCompleted() // 종료
      
            asyncSubject.onNext(4)
            asyncSubject.onNext(5)
  

    subscribe1 : 3
    subscribe2 : 3
    subscribe1 onCompleted
    subscribe2 onCompleted
  

Relay

• PublishRelay,  BehaviorRelay, ReplayRelay
• RxCocoa의 클래스

• .accept()로 이벤트 방출

            let publishRelay = PublishRelay<Int>()
            let subscribe = publishRelay.subscribe{ (next) in
                print("subscribe: ", next.element!)
            }
            publishRelay.accept(1)
            publishRelay.accept(2)
  

    subscribe:  1
    subscribe:  2
  

Subject와 차이

Subject와 2가지 차이점을 빼면 똑같이 동작함

• complete 없음
• error emit 안 함
• 즉 이벤트 보내기만 하고, 종료도 안 됨
• Dispose 전까지 계속 작동하므로 UI Event에서 사용

BehaviorRelay

• .value로 현재 값 꺼낼 수 있음

            let behaviorRelay = BehaviorRelay(value: 0)
            behaviorRelay.accept(1)
            let subscribe = behaviorRelay.subscribe{ (next) in
                print("subscribe: ", next.element!)
            }
            behaviorRelay.accept(2)
            print("value: ", behaviorRelay.value)
  

    subscribe:  1
    subscribe:  2
    value:  2
  

  
  

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음
Publish랑 Behavior 릴레이를 많이 써본 것 같다. 초기값이 필요한 textField와 연동할 때는 Behavior, 네트워크 결과 등 무언가에 대한 결과가 있어야 할 때 등은 Publish 처럼