๐Ÿ“ RxSwift | Observable, Subject, Relay

Thanks to @fimuxd ๐Ÿ–ค

https://github.com/ReactiveX/RxSwift
https://github.com/fimuxd/RxSwift

RxSwift = ์ƒˆ๋กœ์šด ๋ฐ์ดํ„ฐ์— ๋ฐ˜์‘ํ•˜๊ณ  ์ˆœ์ฐจ์ ์œผ๋กœ ๋ถ„๋ฆฌ๋œ ๋ฐฉ์‹ ์ฒ˜๋ฆฌ. ๋น„๋™๊ธฐ์‹ ํ”„๋กœ๊ทธ๋žจ ๊ฐœ๋ฐœ์„ ๊ฐ„์†Œํ™”.

iOS์—์„œ ์ด๋ฏธ ์ œ๊ณต๋œ ๋น„๋™๊ธฐ๋ฅผ ์งค ์ˆ˜ ์žˆ๋Š” API
– Notification Center
– Delegate Pattern
– GCD
– Closure


Section I:
Getting Started with RxSwift

๊ธฐ์ดˆ

3๊ฐ€์ง€ ๊ตฌ์„ฑ์š”์†Œ : Observables(์ƒ์‚ฐ์ž), Operators(์—ฐ์‚ฐ์ž), Schedulers(์Šค์ผ€์ฅด๋Ÿฌ)

1. Observables
Observable<T>
– T ํƒ€์ž…์˜ ๋ฐ์ดํ„ฐ shopshot์„ ์ „๋‹ฌํ•  ์ˆ˜ ์žˆ๋Š” ์ด๋ฒคํŠธ๋ฅผ ๋น„๋™๊ธฐ์ ์œผ๋กœ ์ƒ์„ฑํ•˜๋Š” ๊ธฐ๋Šฅ.
– ๋‹ค๋ฅธ ํด๋ž˜์Šค์—์„œ ๋งŒ๋“  ๊ฐ’์„ ์‹œ๊ฐ„์— ๋”ฐ๋ผ ์ฝ์„ ์ˆ˜ ์žˆ๋‹ค.
– ์ˆ˜์‹  ๊ฐ€๋Šฅ ์œ ํ˜•
next : ์ตœ์‹ , ๋‹ค์Œ ๋ฐ์ดํ„ฐ๋ฅผ ์ „๋‹ฌํ•˜๋Š” ์ด๋ฒคํŠธ
completed : ์ด๋ฒคํŠธ๋ฅผ ์ข…๋ฃŒ์‹œํ‚ค๋Š” ์ด๋ฒคํŠธ (= ๋”์ด์ƒ์˜ ์ด๋ฒคํŠธ ์ƒ์„ฑ์€ ์—†๋‹ค.)
error : Observable ์ด error๋ฅผ ๋ฐœ์ƒ์‹œํ‚ด. ์ถ”๊ฐ€์ ์ธ ์ด๋ฒคํŠธ ์ƒ์„ฑ์€ ์—†๋‹ค.

2. Operators
– ๋น„๋™๊ธฐ ์ž…๋ ฅ์„ ๋ฐ›์•„ ๋ถ€์ˆ˜์ž‘์šฉ ์—†์ด return ์ƒ์„ฑ

3. Schedulers
– Rx์˜ Dispatch Queue.



Architecture
– MVP, MVC, MVVM ๋ชจ๋‘ ๊ฐ€๋Šฅ. MVVM์ด ๊ฐ€์žฅ ํ™œ์šฉ์„ฑ ๋†’์Œ.


RxCocoa
– UI ์ปดํฌ๋„ŒํŠธ์— rx ๋ฅผ ์ถ”๊ฐ€ํ•ด์„œ ์‚ฌ์šฉ.


Observable

– Observable = observable sequence = sequence
Observable ๋“ค์€ ์ผ์ • ๊ธฐ๊ฐ„๋™์•ˆ ๊ณ„์†ํ•ด์„œ ์ด๋ฒคํŠธ๋ฅผ ์ƒ์„ฑํ•˜๊ณ , ์ด๊ฑธ emitting(๋ฐฉ์ถœ) ์ด๋ผ๊ณ  ํ•œ๋‹ค.
– ์ด๋ฒคํŠธ๋“ค์€ ์ˆซ์ž๋‚˜ ์ธ์Šคํ„ด์Šค ๋“ฑ์˜ ๊ฐ’์„ ๊ฐ€์งˆ ์ˆ˜ ์žˆ๊ณ , ํƒญ๊ณผ ๊ฐ™์€ ์ œ์Šค์ฒ˜ ์ธ์‹๋„ ๊ฐ€๋Šฅ.



์ƒ๋ช…์ฃผ๊ธฐ
Observable์€ ์–ด๋–ค ๊ตฌ์„ฑ์š”์†Œ๋ฅผ ๊ฐ€์ง€๋Š” next ์ด๋ฒคํŠธ๋ฅผ ๊ณ„์†ํ•ด์„œ ๋ฐฉ์ถœ ๊ฐ€๋Šฅ.
Observable์€ error ์ด๋ฒคํŠธ๋ฅผ ๋ฐฉ์ถœํ•ด์„œ ์™„์ „ ์ข…๋ฃŒ ๊ฐ€๋Šฅ.
error๋Š” Swift.Error
Observable์€ complete ์ด๋ฒคํŠธ๋ฅผ ๋ฐฉ์ถœํ•ด์„œ ์™„์ „ ์ข…๋ฃŒ ๊ฐ€๋Šฅ.
– instance ์—†์ด ๋ฐ”๋กœ ์ข…๋ฃŒ.



Observable(Observable Sequence) ์ •์˜

let one = 1
let two = 2
let three = 3

// just = ์ •์˜ํ•œ ํƒ€์ž…์˜ Observable Sequence ๋ฅผ ์ƒ์„ฑ.
let observable: Observable<Int> = Observable<Int>.just(1)

// of = ํƒ€์ž… ์ถ”๋ก ์„ ํ†ตํ•ด Observable Sequence ์ƒ์„ฑ.
let observable2 = Observable.of(one, two, three)
let observable3 = Observable.of([one, two, three])

// from = array์˜ ๊ฐ๊ฐ์˜ ์š”์†Œ๋ฅผ ํ•˜๋‚˜์”ฉ ๋ฐฉ์ถœํ•˜๋Š” Sequence.
let observable4 = Observable.from([one, two, three])

just : ํƒ€์ž…๊ณผ ํ•จ๊ป˜ ์ •์˜
of : ํƒ€์ž… ์ถ”๋ก 
from : Array์˜ ๊ฐ๊ฐ์˜ ๊ฐ’์„ ๊ฐ๊ฐ์˜ ์š”์†Œ๋กœ ํ•˜๋Š” Observable sequence๊ฐ€ ๋จ.



Observable ๊ตฌ๋…(subscribing)
Observable์€ ๊ตฌ๋…์ž์ด๊ธฐ ๋•Œ๋ฌธ์— ๊ตฌ๋…๋˜๊ธฐ ์ „์—๋Š” ์•„๋ฌด๋Ÿฐ ์ด๋ฒคํŠธ๋„ ๋ณด๋‚ด์ง€ ์•Š๋Š”๋‹ค.


1. .subscribe()

let numbers: [Int] = [1, 2, 3]
let observable = Observable.from(numbers)

observable.subscribe { event in
    print(event)
    print(event.element ?? "")
}

// print
next(1)
1
next(2)
2
next(3)
3
completed


2. .subscribe(onNext:)

observable.subscribe(onNext: { num in
    print(num)
}, onError: { error in
    print(error)
}, onCompleted: {
    print("DONE !")
}) {
    //dispose
}

// print
1
2
3
DONE !



3. .empty()

let emptyValue = Observable<Void>.empty()

– ํ™œ์šฉ ์˜ˆ
– ์ฆ‰์‹œ ์ข…๋ฃŒํ•  ์ˆ˜ ์žˆ๋Š” Observable ์„ ๋ฆฌํ„ดํ•˜๊ณ  ์‹ถ์„ ๋•Œ.
– ์˜๋„์ ์œผ๋กœ 0๊ฐœ์˜ ๊ฐ’์„ ๊ฐ€์ง€๋Š” observable์„ ๋ฆฌํ„ดํ•˜๊ณ  ์‹ถ์„ ๋•Œ


4. .never()

let emptyValue = Observable<Void>.never()
let disposeBag = DisposeBag()
let observable = Observable<Void>.never()

observable
    .do(onSubscribe: {
        print("Subscribed !")
    })
    .subscribe(onNext: { element in
        print(element)
    }, onCompleted: {
        print("COMPLETED!")
    })
    .disposed(by: disposeBag)

// print๊ฒฐ๊ณผ
Subscribed !

do


5. .range()

let observable = Observable<Int>.range(start: 0, count: 5)




Disposing๊ณผ ์ข…๋ฃŒ
– subscrption = observable ์ด ์ด๋ฒคํŠธ๋ฅผ ๋ฐฉ์ถœํ•˜๋Š” ๋ฐฉ์•„์‡ 
– unsubscription = observable ์„ ์ˆ˜๋™์ ์œผ๋กœ ์ข…๋ฃŒ = Dispose
– dispose ํ•˜์ง€ ์•Š์œผ๋ฉด ๋ฉ”๋ชจ๋ฆฌ ๋ˆ„์ˆ˜ …………… ๐Ÿ˜ก

1. .dispose()

let subscription = observable.subscribe { event in
    print(event)
}

subscription.dispose()

2. DisposeBag()
– ๊ฐ๊ฐ์˜ subscription์„ ๊ด€๋ฆฌํ•˜๋Š”๊ฑด ์ƒ๋‹นํžˆ ๋น„ํšจ์œจ์ .

let disposeBag = DisposeBag()
subscription.disposed(by: disposeBag)

– disposable์€ Dispose bag์ด ํ• ๋‹น ํ•ด์ œํ•˜๋ ค๊ณ  ํ•  ๋•Œ๋งˆ๋‹ค dispose() ๋ฅผ ํ˜ธ์ถœ.


3. .create(:)

Observable<Int>.create { observer -> Disposable in
    observer.onNext(1)
    observer.onNext(2)

    return Disposables.create()
}.subscribe(onNext: { num in
    print(1)
}) {
    print("Disposed")
}.disposed(by: disposeBag)

– error, complete ์—†์ด๋„ observable sequence์— ๋”์ด์ƒ ์—†์œผ๋ฉด ์ข…๋ฃŒ๊ฐ€๋˜๊ณ  dispose ๋œ๋‹ค.





Observable Factory ๋งŒ๋“ค๊ธฐ
– Observable Factory : ๊ฐ subscriber์—๊ฒŒ ์ƒˆ๋กญ๊ฒŒ Observable ํ•ญ๋ชฉ์„ ์ œ๊ณตํ•˜๋Š” ๊ฒƒ. (๊ณต์šฉ์ ์ธ ๊ฐœ๋… ์•„๋‹˜.)
.deferred : Observable์„ ๋ฆฌํ„ดํ•˜๋Š” ๋ฉ”์†Œ๋“œ. subscribe ๋  ๋•Œ ์‹คํ–‰๋œ๋‹ค.

let disposeBag = DisposeBag()
var isTrue = true

let factory: Observable<Int> = Observable.deferred {
    isTrue.toggle()

    if isTrue {
        return Observable.of(1, 2, 3)
    } else {
        return Observable.of(4, 5, 6)
    }
}

for _ in 0...3 {
    factory
        .subscribe { print($0) }
        .disposed(by: disposeBag)
}




Traits ์‚ฌ์šฉ
– ์ข์€ ๋ฒ”์œ„์˜ Observable. (?????????????????)

1. Single

let observable = Observable<Int>.just(0)
observable.asSingle()

let subject = PublishSubject<Int>()
subject.asSingle()

– ๋‘ ๊ฐ€์ง€ ์ด๋ฒคํŠธ ๋ฐฉ์ถœ : .success(value), .error
.success(value) = .next + .completed
– ์‚ฌ์šฉ ์˜ˆ : ์„ฑ๊ณต, ์‹คํŒจ๋กœ ํ™•์ธ๋  ์ˆ˜ ์žˆ๋Š” 1ํšŒ์„ฑ ํ”„๋กœ์„ธ์Šค(๋ฐ์ดํ„ฐ ๋‹ค์šด๋กœ๋“œ ๋“ฑ)

2. Completable

let completable = Completable.create(subscribe: (@escaping Completable.CompletableObserver) -> Disposable)

– ๋‘ ๊ฐ€์ง€ ์ด๋ฒคํŠธ ๋ฐฉ์ถœ : .completed, .error
observable์„ completable๋กœ ๋ณ€๊ฒฝ์€ ๋ถˆ๊ฐ€๋Šฅ.
– ์‚ฌ์šฉ ์˜ˆ : ์—ฐ์‚ฐ์ด ์ œ๋Œ€๋กœ ์™„๋ฃŒ๋˜์—ˆ๋Š”์ง€๋งŒ ํ™•์ธํ•  ๋•Œ.

3. Maybe

let observable = Observable<Int>.just(0)
observable.asMaybe()

let subject = PublishSubject<Int>()
subject.asMaybe()

1. Single + 2. Completable
.success(value), .completed, .error. 3๊ฐ€์ง€ ๋ชจ๋‘ ๋ฐฉ์ถœ ๊ฐ€๋Šฅ.
.complete ๋˜๋”๋ผ๋„ ์•„๋ฌด ๊ฐ’์„ ๋ฐฉ์ถœํ•˜์ง€ ์•Š๋Š”๋‹ค.



Debug

let disposeBag = DisposeBag()
let observable = Observable<Void>.never()

observable
    .debug("DEBUG")
    .subscribe()
    .disposed(by: disposeBag)

// ์‹คํ–‰ ๊ฒฐ๊ณผ
2020-05-28 17:00:40.348: DEBUG -> subscribed
2020-05-28 17:00:40.350: DEBUG -> isDisposed




Subjects

์‹ค์‹œ๊ฐ„์œผ๋กœ Observable์— ์ƒˆ๋กœ์šด ๊ฐ’์„ ์ถ”๊ฐ€ํ•˜๊ณ  subscriber์—๊ฒŒ ๋ฐฉ์ถœํ•˜๋Š” ๊ฒƒ.
Observable์ด์ž Observal.
Subject = Observable + Observer

subject๋Š” .next ์ด๋ฒคํŠธ๋ฅผ ๋ฐ›๊ณ , ์ด๋ฒคํŠธ๋ฅผ ๋ฐ›์„ ๋•Œ๋งˆ๋‹ค subscriber์—๊ฒŒ ๋ฐฉ์ถœํ•œ๋‹ค.
subscriber๊ฐ€ ์กด์žฌํ•˜์ง€ ์•Š๋Š” ์ด์ƒ, subject์— ์ƒˆ๋กœ์šด ๊ฐ’์„ ์ถ”๊ฐ€ํ•ด๋„ ์‹คํ–‰๋˜์ง€ ์•Š๋Š”๋‹ค.



Subject ์˜ ์ข…๋ฅ˜ (4๊ฐ€์ง€)
PublishSubject : ๋นˆ ์ƒํƒœ๋กœ ์‹œ์ž‘ํ•˜์—ฌ ์ƒˆ๋กœ์šด ๊ฐ’๋งŒ์„ subscriber์—๊ฒŒ ๋ฐฉ์ถœ.
BehaviorSubject : ํ•˜๋‚˜์˜ ์ดˆ๊ธฐ๊ฐ’์„ ๊ฐ€์ง„ ์ƒํƒœ๋กœ ์‹œ์ž‘. ์ƒˆ๋กœ์šด subscriber์—๊ฒŒ ์ดˆ๊ธฐ๊ฐ’ ๋˜๋Š” ์ตœ์‹ ๊ฐ’์„ ๋ฐฉ์ถœ
ReplaySubject : ๋ฒ„ํผ๋ฅผ ๋‘๊ณ  ์ดˆ๊ธฐํ™”. ๋ฒ„ํผ ์‚ฌ์ด์ฆˆ ๋งŒํผ์˜ ๊ฐ’๋“ค์„ ์œ ์ง€ํ•˜๋ฉด์„œ ์ƒˆ๋กœ์šด subscriber ์—๊ฒŒ ๋ฐฉ์ถœ
Variable : BehaviorSubject ๋ฅผ ๋ž˜ํ•‘ํ•˜๊ณ  ํ˜„์žฌ์˜ ๊ฐ’์˜ ์ƒํƒœ๋กœ ๋ณด์กด. ๊ฐ€์žฅ ์ตœ์‹ /์ดˆ๊ธฐ ๊ฐ’๋งŒ์„ ์ƒˆ๋กœ์šด subscriber ์—๊ฒŒ ๋ฐฉ์ถœ โ†’ BehaviorRelay




PublishSubjects
– ๊ตฌ๋…ํ•˜๋Š” ์ˆœ๊ฐ„, ์ƒˆ๋กœ์šด ์ด๋ฒคํŠธ ์ˆ˜์‹ ์„ ์•Œ๋ฆฌ๊ณ  ์‹ถ์„ ๋•Œ ์šฉ์ด.
.complete, .error ๋ฅผ ํ†ตํ•ด Subject๊ฐ€ ์™„์ „ ์ข…๋ฃŒ๋  ๋•Œ๊นŒ์ง€ ์ง€์†.
– ํ™œ์šฉ ์˜ˆ : ์‹œ๊ฐ„์— ๋ฏผ๊ฐํ•œ ๋ฐ์ดํ„ฐ๋ฅผ ๋ชจ๋ธ๋งํ•  ๋•Œ.


BehaviorSubjects

https://github.com/fimuxd/RxSwift/blob/master/Lectures/03_Subjects/Ch3.%20Subjects.md

– ์ƒˆ๋กœ์šด subscriber ๋“ฑ๋ก ์ „, ๋งˆ์ง€๋ง‰ .next ์ด๋ฒคํŠธ๋ฅผ ์ƒˆ๋กœ์šด subscriber ์—๊ฒŒ ๋ฐ˜๋ณต์‹œํ‚ด.
– ๊ทธ๋ž˜์„œ ํ•˜๋‚˜์˜ ์ดˆ๊ธฐ๊ฐ’์ด ํ•„์š”.
– ์ด๊ฑธ ์ œ์™ธํ•˜๋ฉด PublishSubject ์™€ ์œ ์‚ฌ.
– ํ™œ์šฉ ์˜ˆ : ํ™”๋ฉด์„ ์ƒˆ๋กœ Refresh์‹œํ‚ฌ ๋•Œ ์‚ฌ์šฉํ•˜๋ฉด ์œ ์šฉ
(์ด์ „์˜ ๊ฐ€์žฅ ์ตœ์‹  ๋ฐ์ดํ„ฐ๋ฅผ ํ‘œ์‹œ์‹œํ‚จ ํ›„, ์ƒˆ๋กœ์šด ๊ฐ’์ด ์˜ค๋ฉด ๋ฐ”๋กœ ํ‘œ์‹œ์‹œํ‚ฌ ์ˆ˜ ์žˆ๋‹ค.)




ReplaySubject

let disposeBag = DisposeBag()

let subject = ReplaySubject<String>.create(bufferSize: 2)
subject.onNext("1")
subject.onNext("2")
subject.onNext("3")

subject
    .subscribe { print("1: ($0)") }
    .disposed(by: disposeBag)

// print ๊ฒฐ๊ณผ
1: next(2)
1: next(3)

bufferSize ๊ฐœ์˜ ์ด๋ฒคํŠธ๋ฅผ ์ €์žฅํ–ˆ๋‹ค๊ฐ€ subscribe ๋˜๋ฉด ์ €์žฅ๋œ ์ด๋ฒคํŠธ๋ฅผ ๋ชจ๋‘ ๋ฐฉ์ถœ.



Variable(Deprecated)
BehaviorSubject ์˜ ํ˜„์žฌ๊ฐ’์€ value ํ”„๋กœํผํ‹ฐ๋ฅผ ํ†ตํ•ด์„œ ์•Œ ์ˆ˜ ์žˆ๋‹ค.
.complete, .error ๋Š” ์‚ฌ์šฉํ•  ์ˆ˜ ์—†๋‹ค. value ์˜ ๋ณ€ํ™”์˜ ์ƒ๊ฒผ์„ ๋•Œ์˜ .next๋ฟ.
– ๋ฉ”๋ชจ๋ฆฌ ํ• ๋‹น์ด ํ•ด์ œ๋˜์—ˆ์„ ๋•Œ ์ž๋™์ ์œผ๋กœ .completed
– ํ™œ์šฉ ์˜ˆ : ์œ ์ € ์ƒํƒœ๋ฅผ ๋‚˜ํƒ€๋‚ด์•ผ ํ•  ๋•Œ. (๋กœ๊ทธ์•„์›ƒ ๋‹นํ–ˆ์„ ๋•Œ์˜ ์ฒ˜๋ฆฌ ๋“ฑ)

BehaviorRelay๋กœ ์‚ฌ์šฉ.



Replay (RxCocoa)
PublishRelay, BehaviorRelay ์˜ ๋‘ ์ข…๋ฅ˜๊ฐ€ ์กด์žฌ.
– ์ฐจ์ด์  : BehaviorRelay ์—์„œ๋Š” ํ˜„์žฌ๊ฐ’์„ ์•Œ ์ˆ˜ ์žˆ๋Š” .value๊ฐ€ ์กด์žฌ.
– ๊ณตํ†ต์  : .onNext๊ฐ€ ์—†์–ด์ง€๊ณ , .accept ๊ฐ€ ๊ฐ™์€ ์—ญํ• .

BehaviorRelay
.valueํ†ตํ•ด์„œ ํ˜„์žฌ์˜ ๊ฐ’์„ ๊ฐ€์ ธ์˜ฌ ์ˆ˜ ์žˆ๋‹ค. get-property
.value๋ฅผ ๋ณ€๊ฒฝํ•˜๊ธฐ ์œ„ํ•ด์„œ๋Š” .accept
Variable์˜ ์—ญํ• ์„ ์ˆ˜ํ–‰.

let relay = BehaviorRelay<String>(value: "1")

relay
    .asObservable()
    .subscribe { print("1: ($0)") }
    .disposed(by: disposeBag)

relay.accept("2")

relay
    .asObservable()
    .subscribe { print("2: ($0)") }
    .disposed(by: disposeBag)

relay.accept("3")




Subject vs Relay
– subject๋Š” .complete, .error ๊ฐ€ ๋ฐœ์ƒ๋˜๋ฉด ์ข…๋ฃŒ๋˜์ง€๋งŒ Relay ๋Š” Dispose๋˜๊ธฐ ์ „๊นŒ์ง€ ๊ณ„์† ์ž‘๋™ํ•œ๋‹ค.
– .complete ๋‚˜ .error ๊ฐ€ ๋ฐœ์ƒํ•˜๋ฉด ์•ˆ๋˜๋Š” ๊ฒฝ์šฐ. ๊ณ„์†ํ•ด์„œ sequence๊ฐ€ ์ƒ์„ฑ๋˜์–ด์•ผ ํ•  ๋•Œ ์‚ฌ์šฉ.
– UIEvent์—์„œ๋Š” Relay๊ฐ€ ์ ์ ˆ.




Practice : Observables & Subjects

CODE
https://gist.github.com/unnnyong/9cf91f1849b5ab9d7facd4757359ec4f




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