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EVERYDAY REACTIVE
毎⽇日リアクティブ
Agnes Vasarhelyi @vasarhelyia
! Ustream (IBM Cloud Video)
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No content
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"Reactive programming manages asynchronous
data flows between sources of data and
components that need to react to that data."
MATT GALLAGHER, COCOAWITHLOVE.COM
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• Reduces state
• Less, but more concise code
• Easier to read
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IS THERE A FRAMEWORK FOR THAT?
There are plenty.
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WHEN DO I APPLY IT?
Depends on complexity.
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WHERE DO I APPLY IT?
• MVVM
• async ops
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OBSERVATION
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let (signal, observer) = Signal.pipe()
signal.observeValues { animal in print( "value: \(animal)") }
observer.sendNext(value: "")
observer.sendNext(value: "")
> value:
> value:
ReactiveSwift (RAC)
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LET'S REDUCE SOME STATE
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var loading: Bool
var userLoggedIn: Bool
var didShowAlert: Bool
var loading =
reactive(userLoggedIn) &&
reactive(didShowAlert)
23 STATE 22 STATE
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TRANSFORM / COMBINE
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let userLoggedIn = PublishSubject()
let didLoadContent = PublishSubject()
let loading = Observable.combineLatest(userLoggedIn, didLoadContent) {
!($0 && $1)
}
loading.subscribe(onNext: { print("loading: \($0)") })
userLoggedIn.onNext(false)
didLoadContent.onNext(false)
userLoggedIn.onNext(true)
didLoadContent.onNext(true)
> loading: true
> loading: true
> loading: false
RxSwift
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SIMPLIFY / UNIFY ASYNC OPERATIONS
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let catButton = UIButton(title: "")
let url = URL(string: "http://catfacts-api.appspot.com/api/facts?
number=1")
let catFact = URLSession.shared.rx.json(url:url!)
.map( { return "\(parsedCatFact($0))" })
Observable.combineLatest(catButton.rx.tap, catFact) { c, fact in
"\(c) \(fact)"
}.subscribe(onNext: { print("\($0)") })
> : Cats can be right-pawed or left-pawed.
> : In 1987 cats overtook dogs as the number one pet in America.
RxSwift
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TRADE-OFFS,
COMPLICATIONS
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1. DEBUGGING
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HOW TO HELP IT?
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func logAnimals() {
let animal = MutableProperty("")
let animalStream = animal.producer.logEvents(identifier: "")
animalStream.start()
animal.value = ""
}
[] starting fileName: (...)/A.swift, functionName: logAnimals(), lineNumber: 16
[] value fileName: (...)/A.swift, functionName: logAnimals(), lineNumber: 16
[] started fileName: (...)/A.swift, functionName: logAnimals(), lineNumber: 16
[] value fileName: (...)/A.swift, functionName: logAnimals(), lineNumber: 16
...
ReactiveSwift (RAC)
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2. "FANCY KVO"
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viewModel.title.observeNext { [weak self] v in
self?.titleLabel.text = v
self?.refreshButton.enabled = true
self?.canRefresh = true
})
func update() {
if (!self.canRefresh) return;
...
}
Bond
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viewModel.title.bind(to: titleLabel)
Bond
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viewModel.title.map { n -> Bool in
return n != nil
}.bind(to: refreshButton.reactive.isEnabled)
Bond
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viewModel.title.bind(to: titleLabel)
viewModel.title
.bidirectionalBind(to: titleTextField.reactive.bnd_text)
Bond
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3. INJECT SIDE EFFECTS CAREFULLY
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let catFact = URLSession.shared.rx.json(url:url!)
.map( { return "\(parsedCatFact($0))" })
.do(onNext: { _ in
print("EFFECT")
})
catFact.subscribe(onNext: { print("1. : \($0)") })
catFact.subscribe(onNext: { print("2. : \($0)") })
> EFFECT
> 1. : Most cats adore sardines.
> EFFECT
> 2. : Cats take between 20-40 breaths per minute.
RxSwift
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...
.do(onNext: { fact in
Analytics.trackEvent("cat fact generated: \(fact)")
})
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4. AVOID CHAOS
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Thread 1
eraseButton.reactive.tap.onNext( {
stateManager.items.remove($0)
})
Thread 2
apiResponse.onNext ( {
stateManager.items.append($0)
})
eraseButton.reactive.tap.onNext( {
stateManager.removeItem($0)
}).onScheduler(MainScheduler)
apiResponse.onNext ( {
stateManager.appendItem($0)
}).onScheduler(BackgroundScheduler)
immutability + schedulers =
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...
.ignoreNil()
.flatMapLatest { $0.unwrap }
.collect()
.first()
.filter(include: { s -> Bool in
return s.characters.count > 3
})
.merge(with: offlineSignal.distinct())
.combineLatest(with: viewModel.title.map { t -> Bool in
return t != nil
}).bind(to: refreshButton.reactive.isEnabled)
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NO MORE
IMPERATIVE?
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DESIGNING APIS
• don't expose reactive,
• support it
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THANKS
@vasarhelyia
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RESOURCES
https://github.com/ReactiveKit/Bond
https://github.com/ReactiveX/RxSwift
https://github.com/ReactiveCocoa/ReactiveCocoa
https://github.com/mattgallagher/CwlSignal
https://www.cocoawithlove.com/blog/reactive-programming-what-and-why.html
https://www.youtube.com/watch?v=7AqXBuJOJkY
https://speakerdeck.com/joshaber/better-code-for-a-better-world
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