[RxSwift] Observable의 공유

1. Observable의 라이프사이클

Observable.just(1).debug("just").subscribe().dispose()

2019-04-04 12:14:44.633: just -> subscribed

2019-04-04 12:14:44.703: just -> Event next(1)

2019-04-04 12:14:44.710: just -> Event completed

2019-04-04 12:14:44.710: just -> isDisposed

 

 

2. Observable의 공유

 

- 옵저버블을 공유하지 않으면 subscribe 횟수 만큼 이벤트가 발생한다
- API Call을 하는 Observable을 두번 subscribe하면 API Call이 두번 일어난다 

 

2.1 Observable을 공유하지 않았을 때 

       let observable = Observable<Int>.interval(1, scheduler: MainScheduler.instance).take(2).map { (element) -> Int in
            print("map : \(element)")
            return element
        }
        
        observable.subscribe(onNext: { (element) in
            print("observable subscribe1 : \(element)")
        }).disposed(by: disposeBag)
        
        observable.subscribe(onNext: { (element) in
            print("observable subscribe2 : \(element)")
        }).disposed(by: disposeBag)

 

map : 0

observable subscribe1 : 0

map : 0

observable subscribe2 : 0

map : 1

observable subscribe1 : 1

map : 1

observable subscribe2 : 1


=> map이 observable마다 2개씩 출력되는 것을 보니 observable이 공유되지 않고 있음!!

 

 

2.2 ConnectableObservable 

extension ObservableType {

    /**
    Returns a connectable observable sequence that shares a single subscription to the underlying sequence.

    This operator is a specialization of `multicast` using a `PublishSubject`.

    - seealso: [publish operator on reactivex.io](http://reactivex.io/documentation/operators/publish.html)

    - returns: A connectable observable sequence that shares a single subscription to the underlying sequence.
    */
    public func publish() -> ConnectableObservable<E> {
        return self.multicast { PublishSubject() }
    }
}

 

이 publish 메소드를 사용해서 ConnectableObservable을 만들 수 있다 

 

        let observable = Observable<Int>.interval(1, scheduler: MainScheduler.instance).take(2).map { (element) -> Int in
            print("map : \(element)")
            return element
        }
        
        let connectableObservable: ConnectableObservable<Int> = observable.publish()
        
        connectableObservable.subscribe(onNext: { (element) in
            print("connectableObservable subscribe1 : \(element)")
        }).disposed(by: disposeBag)
        
        connectableObservable.subscribe(onNext: { (element) in
            print("connectableObservable subscribe2 : \(element)")
        }).disposed(by: disposeBag)
        
        // connect해줘야지 시퀀스가 시작됨--!
        connectableObservable.connect().disposed(by: disposeBag)

 

map : 0

connectableObservable subscribe1 : 0

connectableObservable subscribe2 : 0

map : 1

connectableObservable subscribe1 : 1

connectableObservable subscribe2 : 1

 

=>  observable이 공유되고 있음!! 

 

 

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RxSwift, subscriptions 의 공유