Reactive Thinking in iOS Development

In a world where Imperative Programming is the most used paradigm, Reactive comes up to make our code more reusable, robust, and stateless. Learn what Functional Reactive Programming means and how it could help you with problems you have to face daily in your projects. We’ll present basic concepts and practical examples for iOS developers that will help you to start thinking in streams, observers, .. and mix them with cool Swift functional concepts.

Transcript

1. REACTIVE THINKING IN IOS DEVELOPMENT @PEPIBUMUR / @SAKY
2. 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
3. INDEX > Programming Paradigms > Reactive Libraries > Reactive Motivation > Reactive Thinking > Reactive Caveats > Conclusion
4. PARADIGMS ! WAYS OF SEEING THE WORLD WHEN IT COMES TO PROGRAMMING
5. 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
6. IMPERATIVE PROGRAMMING DECLARATIVE PROGRAMMING
7. IMPERATIVE PROGRAMMING DECLARATIVE PROGRAMMING
8. HOW SEQUENCE OF STEPS THAT HAPPEN IN ORDER
9. NATURAL WAY TO PROGRAM
10. EXECUTION STATE (AKA SIDE EFFECT)
11. IMPERATIVE PROGRAMMING func userDidSearch(term: String) { let apiReults = api.search(term: term).execute() self.items = self.adaptResults(apiResults) self.tableView.reloadData() }
12. IMPERATIVE PROGRAMMING DECLARATIVE PROGRAMMING
13. WHAT IT DOESN'T DESCRIBE THE CONTROL FLOW
14. HTML
15. HTML SQL
16. HTML SQL REACTIVE PROGRAMMING
17. DECLARATIVE PROGRAMMING let predicate = NSPredicate(format: "name == %@", "Pedro") let regex = NSRegularExpression(pattern: ".+", options: 0)
18. REACTIVE PROGRAMMING DATA-FLOW PROGRAMMING (DESCRIBES THE STATE PROPAGATION) # THE INTRODUCTION TO REACTIVE PROGRAMMING THAT YOU'VE BEEN MISSING
19. FUNCTIONAL REACTIVE PROGRAMMING (AKA FRP)
20. REACTIVE LIBRARIES > RxSwift (ReactiveX) > ReactiveCocoa > BrightFutures > ReactKit > Bond > More and more... PromiseKit, Bolts...
21. WHAT LIBRARY SHOULD I USE? !
22. WHAT LIBRARY SHOULD I USE? ! DO I NEED A LIBRARY FOR THIS? !
23. SWIFT var userName: String { didSet { // React to changes in variables } }
24. SWIFT var userName: String { didSet { // React to changes in variables view.updateTitle(userName) } }
25. MOTIVATION ! WHY SHOULD I STICK TO REACTIVE PROGRAMMING?
26. > Bindings > Composability > Threading
27. > Bindings > Composability > Threading
28. BINDING
29. UI BINDING
30. UI BINDING
31. UI BINDING
32. > Bindings > Composability > Threading
35. > Bindings > Composability > Threading
36. > Bindings > Composability > Threading (observer and execution)
37. THREADING
38. REACTIVE THINKING !
39. THINKING IN TERMS OF OBSERVABLES OR SIGNALS/PRODUCERS IN REACTIVECOCOA
40. ACTIONS CAN BE OBSERVED HOW? !
41. .NEXT(T) .ERROR(ERRORTYPE) .COMPLETE
42. OPERATIONS RxSwift Observable<String>.create { (observer) -> Disposable in observer.onNext("next value") observer.onCompleted() return NopDisposable.instance // For disposing the action } ReactiveCocoa SignalProducer<String>.create { (observer, disposable) in observer.sendNext("next value") observer.sendComplete() }
43. EXISTING PATTERNS RXSWIFT ▶︎ RXCOCOA (EXTENSIONS) REACTIVECOCOA ▶︎ DO IT YOURSELF
44. UIKIT let button = UIButton() button.rx_controlEvent(.TouchUpInside) .subscribeNext { _ in print("The button was tapped") }
45. NOTIFICATIONS NSNotificationCenter.defaultCenter() .rx_notification("my_notification", object: nil) .subscribeNext { notification // We got a notification }
46. DELEGATES self.tableView.rx_delegate // DelegateProxy .observe(#selector(UITableViewDelegate.tableView(_:didSelectRowAtIndexPath:))) .subscribeNext { (parameters) in // User did select cell at index path }
47. PLAYING ! WITH OBSERVABLES
48. OBSERVABLE let tracksFetcher = api.fetchTracks // Background .asObservable()
49. ERROR HANDLING let tracksFetcher = api.fetchTracks // Background .asObservable() .retry(3) .catchErrorJustReturn([])
50. MAPPING let tracksFetcher = api.fetchTracks // Background .asObservable() .retry(3) .catchErrorJustReturn([]) .map(TrackEntity.mapper().map)
51. FILTERING let tracksFetcher = api.fetchTracks // Background .asObservable() .retry(3) .catchErrorJustReturn([]) .map(TrackEntity.mapper().map) .filter { $0.name.contains(query) }
52. 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) }
53. 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
54. 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) }) }) } } }
55. 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 }
56. OTHER OPERATORS Combining / Skipping Values / Deferring / Concatenation / Take some values / Zipping
57. OBSERVING ! EVENTS
58. SUBSCRIBING observable subscribe { event switch (event) { case .Next(let value): print(value) case .Completed: print("completed") case .Error(let error): print("Error: \(error)") } }
59. BIND CHANGES OVER THE TIME TO AN OBSERVABLE OBSERVABLE ▶ BINDING ▶ OBSERVER
60. BINDING To a Variable let myVariable: Variable<String> = Variable("") observable .bindTo(myVariable) print(myVariable.value) To UI observable .bindTo(label.rx_text)
62. ! CAVEATS BECAUSE YES... IT COULDN'T BE PERFECT
63. DEBUGGING DEBUG OPERATOR IN RXSWIFT
64. 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
65. 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
66. //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
67. > [after_fetch] Next Event... // Downloaded tracks > [mapped_results] Error ... // Detected error after mapping > [...]
68. RETAIN CYCLES class IssuePresenter { var disposable: Disposable func fetch() { self.disposable = issueTitle .observable() .bindTo { self.titleLabel.rx_text } } }
69. UNSUBSCRIPTION YOU NEED TO TAKE CARE OF THE LIFECYCLE OF YOUR OBSERVABLES
70. UNSUBSCRIPTION title.asObservable().bindTo(field.rx_text) // RxSwift will show a warning
71. UNSUBSCRIPTION let titleDisposable = title.asObservable().bindTo(field.rx_text) titleDisposable.dispose()
72. UNSUBSCRIPTION let disposeBag = DisposeBag() title.asObservable() .bindTo(field.rx_text) .addDisposableTo(disposeBag) // The binding is active until the disposeBag is deallocated
73. CONCLUSIONS
74. PREVENTS STATEFUL CODE
75. DATA FLOW MANIPULATION BECOMES EASIER
76. BUT... !
77. YOU COUPLE YOUR PROJECT TO A LIBRARY !
78. REACTIVE CODE SPREADS LIKE A VIRUS ! OVERREACTIVE ⚠
79. DEFINE REACTIVE DESIGN GUIDELINES AND STICK TO THEM
80. HAVE REACTIVE FUN !
81. REFERENCES > rxmarbles.com > RxSwift Community > RxSwift Repository > ReactiveCocoa
82. WE ARE HIRING PEPI@SOUNDCLOUD.COM - ISAAC@LETGO.COM ❄ BERLIN - BARCELONA !
84. THANKS QUESTIONS? SLIDES HTTP://BIT.LY/1RFWLCI @SAKY - @PEPIBUMUR