REACTIVE THINKING IN IOS DEVELOPMENT @PEPIBUMUR / @SAKY 

WHO? @pepibumur iOS Developer at SoundCloud GitHub: pepibumur Twitter: pepibumur @saky iOS Developer at Letgo GitHub: isaacroldan Twitter: saky GitDo.io our spare time project 

INDEX > Programming Paradigms > Reactive Libraries > Reactive Motivation > Reactive Thinking > Reactive Caveats > Conclusion 

PARADIGMS ! WAYS OF SEEING THE WORLD WHEN IT COMES TO PROGRAMMING 

WIKIPEDIA Data-Driven, Declarative, Dynamic, End-User, Event-Driven, Expression-Oriented, Feature-Oriented, Function-level, Generic, Imperative, Inductive, Language Oriented, Metaprogramming, Non-Structured, Nondeterministic, Parallel computing, Point-free Style, Structured, Value- Level, Probabilistic 

IMPERATIVE PROGRAMMING DECLARATIVE PROGRAMMING 

IMPERATIVE PROGRAMMING DECLARATIVE PROGRAMMING 

HOW SEQUENCE OF STEPS THAT HAPPEN IN ORDER 

NATURAL WAY TO PROGRAM 

EXECUTION STATE (AKA SIDE EFFECT) 

IMPERATIVE PROGRAMMING func userDidSearch(term: String) { let apiReults = api.search(term: term).execute() self.items = self.adaptResults(apiResults) self.tableView.reloadData() } 

IMPERATIVE PROGRAMMING DECLARATIVE PROGRAMMING 

WHAT IT DOESN'T DESCRIBE THE CONTROL FLOW 

HTML 

HTML SQL 

HTML SQL REACTIVE PROGRAMMING 

DECLARATIVE PROGRAMMING let predicate = NSPredicate(format: "name == %@", "Pedro") let regex = NSRegularExpression(pattern: ".+", options: 0) 

REACTIVE PROGRAMMING DATA-FLOW PROGRAMMING (DESCRIBES THE STATE PROPAGATION) # THE INTRODUCTION TO REACTIVE PROGRAMMING THAT YOU'VE BEEN MISSING 

FUNCTIONAL REACTIVE PROGRAMMING (AKA FRP) 

REACTIVE LIBRARIES > RxSwift (ReactiveX) > ReactiveCocoa > BrightFutures > ReactKit > Bond > More and more... PromiseKit, Bolts... 

WHAT LIBRARY SHOULD I USE? ! 

WHAT LIBRARY SHOULD I USE? ! DO I NEED A LIBRARY FOR THIS? ! 

SWIFT var userName: String { didSet { // React to changes in variables } } 

SWIFT var userName: String { didSet { // React to changes in variables view.updateTitle(userName) } } 

MOTIVATION ! WHY SHOULD I STICK TO REACTIVE PROGRAMMING? 

> Bindings > Composability > Threading 

> Bindings > Composability > Threading 

BINDING 

UI BINDING 

UI BINDING 

UI BINDING 

> Bindings > Composability > Threading 

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> Bindings > Composability > Threading 

> Bindings > Composability > Threading (observer and execution) 

THREADING 

REACTIVE THINKING ! 

THINKING IN TERMS OF OBSERVABLES OR SIGNALS/PRODUCERS IN REACTIVECOCOA 

ACTIONS CAN BE OBSERVED HOW? ! 

.NEXT(T) .ERROR(ERRORTYPE) .COMPLETE 

OPERATIONS RxSwift Observable.create { (observer) -> Disposable in observer.onNext("next value") observer.onCompleted() return NopDisposable.instance // For disposing the action } ReactiveCocoa SignalProducer.create { (observer, disposable) in observer.sendNext("next value") observer.sendComplete() } 

EXISTING PATTERNS RXSWIFT ▶︎ RXCOCOA (EXTENSIONS) REACTIVECOCOA ▶︎ DO IT YOURSELF 

UIKIT let button = UIButton() button.rx_controlEvent(.TouchUpInside) .subscribeNext { _ in print("The button was tapped") } 

NOTIFICATIONS NSNotificationCenter.defaultCenter() .rx_notification("my_notification", object: nil) .subscribeNext { notification // We got a notification } 

DELEGATES self.tableView.rx_delegate // DelegateProxy .observe(#selector(UITableViewDelegate.tableView(_:didSelectRowAtIndexPath:))) .subscribeNext { (parameters) in // User did select cell at index path } 

PLAYING ! WITH OBSERVABLES 

OBSERVABLE let tracksFetcher = api.fetchTracks // Background .asObservable() 

ERROR HANDLING let tracksFetcher = api.fetchTracks // Background .asObservable() .retry(3) .catchErrorJustReturn([]) 

MAPPING let tracksFetcher = api.fetchTracks // Background .asObservable() .retry(3) .catchErrorJustReturn([]) .map(TrackEntity.mapper().map) 

FILTERING let tracksFetcher = api.fetchTracks // Background .asObservable() .retry(3) .catchErrorJustReturn([]) .map(TrackEntity.mapper().map) .filter { $0.name.contains(query) } 

FLATMAPPING let tracksFetcher = api.fetchTracks // Background .asObservable() .retry(3) .catchErrorJustReturn([]) .map(TrackEntity.mapper().map) .filter { $0.name.contains(query) } .flatMap { self.rx_trackImage(track: $0) } 

OBSERVATION THREAD let tracksFetcher = api.fetchTracks // Background .asObservable() .retry(3) .catchErrorJustReturn([]) .map(TrackEntity.mapper().map) .filter { $0.name.contains(query) } .flatMap { self.rx_trackImage(track: $0) } .observeOn(MainScheduler.instance) // Main thread 

LE IMPERATIVE WAY !" func fetchTracks(retry retry: Int = 0, retryLimit: Int, query: query, mapper: (AnyObject) -> Track, completion: ([UIImage], Error?) -> ()) { api.fetchTracksWithCompletion { (json, error) in if let _ = error where retry < retryLimit { fetchTracksWithRetry(retry: retry+1, retryLimit: retryLimit, query: query, mapper: mapper, completion: completion) } else if let error = error { completion([], error) } else if let json = json { guard let jsonArray = json as? [AnyObject] else { completion([], Error.InvalidResponse) return } let mappedTracks = jsonArray.map(mapper) let filteredTracks = mappedTracks.filter { $0.name.contains(query) } self.fetchImages(track: filteredTracks, completion: ([])) let trackImages = self.fetchImages(tracks: filteredTracks, completion: { (images, error) in dispatch_async(dispatch_get_main_queue(),{ if let error = error { completion([], error) return } completion(images, error) }) }) } } } 

THROTTLING CLASSIC REACTIVE EXAMPLE func tracksFetcher(query: String) -> Observable<[TrackEntity]> searchTextField .rx_text.throttle(0.5, scheduler: MainScheduler.instance) .flatmap(tracksFetcher) .subscribeNext { tracks in // Yai! Tracks searched } 

OTHER OPERATORS Combining / Skipping Values / Deferring / Concatenation / Take some values / Zipping 

OBSERVING ! EVENTS 

SUBSCRIBING observable subscribe { event switch (event) { case .Next(let value): print(value) case .Completed: print("completed") case .Error(let error): print("Error: \(error)") } } 

BIND CHANGES OVER THE TIME TO AN OBSERVABLE OBSERVABLE ▶ BINDING ▶ OBSERVER 

BINDING To a Variable let myVariable: Variable = Variable("") observable .bindTo(myVariable) print(myVariable.value) To UI observable .bindTo(label.rx_text) 

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! CAVEATS BECAUSE YES... IT COULDN'T BE PERFECT 

DEBUGGING DEBUG OPERATOR IN RXSWIFT 

let tracksFetcher = api.fetchTracks // Background .asObservable() .retry(3) .catchErrorJustReturn([]) .map(TrackEntity.mapper().map) .filter { $0.name.contains(query) } .flatMap { self.rx_trackImage(track: $0) } .observeOn(MainScheduler.instance) // Main thread 

let tracksFetcher = api.fetchTracks // Background .asObservable .debug("after_fetch") // <-- Debugging probes .retry(3) .catchErrorJustReturn([]) .map(TrackEntity.mapper().map) .debug("mapped_results") // <-- Debugging probes .filter { $0.name.contains(query) } .flatMap { self.rx_trackImage(track: $0) } .observeOn(MainScheduler.instance) // Main thread 

//let tracksFetcher = api.fetchTracks // Background // .asObservable .debug("after_fetch") // <-- Debugging probes // .retry(3) // .catchErrorJustReturn([]) // .map(TrackEntity.mapper().map) .debug("mapped_results") // <-- Debugging probes // .filter { $0.name.contains(query) } // .flatMap { self.rx_trackImage(track: $0) } // .observeOn(MainScheduler.instance) // Main thread 

> [after_fetch] Next Event... // Downloaded tracks > [mapped_results] Error ... // Detected error after mapping > [...] 

RETAIN CYCLES class IssuePresenter { var disposable: Disposable func fetch() { self.disposable = issueTitle .observable() .bindTo { self.titleLabel.rx_text } } } 

UNSUBSCRIPTION YOU NEED TO TAKE CARE OF THE LIFECYCLE OF YOUR OBSERVABLES 

UNSUBSCRIPTION title.asObservable().bindTo(field.rx_text) // RxSwift will show a warning 

UNSUBSCRIPTION let titleDisposable = title.asObservable().bindTo(field.rx_text) titleDisposable.dispose() 

UNSUBSCRIPTION let disposeBag = DisposeBag() title.asObservable() .bindTo(field.rx_text) .addDisposableTo(disposeBag) // The binding is active until the disposeBag is deallocated 

CONCLUSIONS 

PREVENTS STATEFUL CODE 

DATA FLOW MANIPULATION BECOMES EASIER 

BUT... ! 

YOU COUPLE YOUR PROJECT TO A LIBRARY ! 

REACTIVE CODE SPREADS LIKE A VIRUS ! OVERREACTIVE ⚠ 

DEFINE REACTIVE DESIGN GUIDELINES AND STICK TO THEM 

HAVE REACTIVE FUN ! 

REFERENCES > rxmarbles.com > RxSwift Community > RxSwift Repository > ReactiveCocoa 

WE ARE HIRING [email protected] - [email protected] ❄ BERLIN - BARCELONA ! 

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