RxSwift - A primer

The slides for a talk I gave at CocoaHeads Belgium on November 22, 2017 about RxSwift.
The demo project can be found at https://github.com/frederik-jacques/cocoaheads-rxswift-primer

1. RxSwift and how we use it in production apps frederik jacques - @thenerd_be 1
2. Hello frederik jacques - @thenerd_be 2
3. Hello • Frederik Jacques • Lecturer Devine (Howest University College) • Living in The Netherlands (what was I thinking) • Freelance iOS consultant • Currently working at Nederlandse Spoorwegen frederik jacques - @thenerd_be 3
4. frederik jacques - @thenerd_be 4
5. RxSwift frederik jacques - @thenerd_be 5
6. RxSwift • What is it? • Observables / Observers • Subjects • Operators • Debugging • Unit Testing • Live demo frederik jacques - @thenerd_be 6
7. RxSwift • Reactive library • Part of http://reactivex.io • Same api over different language ports frederik jacques - @thenerd_be 7
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9. Nutshell definition frederik jacques - @thenerd_be 9
10. Handling asynchronous code by observing a stream of values. — Yours truly frederik jacques - @thenerd_be 10
11. ! frederik jacques - @thenerd_be 11
12. Remember notifications? frederik jacques - @thenerd_be 12
13. Here we are observing a certain event. NotificationCenter.default .addObserver( forName: Notification.Name.UserDidLogin, object: self, queue: nil ) { (notification) in print("User did login") } frederik jacques - @thenerd_be 13
14. ! Observer Observable frederik jacques - @thenerd_be 14
15. Observable The thing that sends out stuff — Yours truly frederik jacques - @thenerd_be 15
16. Observer The thing that's interested in the data from the observable — Yours truly frederik jacques - @thenerd_be 16
17. Observable • The key element of RxSwift • Concept? • Produce a sequence of immutable events • 3 types of event: next, completed & error frederik jacques - @thenerd_be 17
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19. Types of streams 1. Infinite streams 2. Finite streams • Completes • Errors out frederik jacques - @thenerd_be 19
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23. Subjects frederik jacques - @thenerd_be 23
24. Subjects 1. Variable 2. PublishSubject 3. BehaviorSubject 4. ReplaySubject frederik jacques - @thenerd_be 24
25. Variable • Easiest one to get started with let names = Variable<[String]>(["Frederik"]) frederik jacques - @thenerd_be 25
26. Variable • Get the current value let nameValue = names.value frederik jacques - @thenerd_be 26
27. Variable • Getting updates names.asObservable() .subscribe(onNext: { (theNames) in print(theNames) }) frederik jacques - @thenerd_be 27
28. Variable • Putting elements on the stream names.value.append("Tom") names.value.append("Spencer") frederik jacques - @thenerd_be 28
29. Variable • Putting it all together let names = Variable<[String]>(["Frederik"]) names.asObservable() .subscribe(onNext: { (theNames) in print(theNames) }) names.value.append("Tom") names.value.append("Spencer") frederik jacques - @thenerd_be 29
30. PublishSubject • Subscribers get all the upcoming events (NOT the current one) let nameSubject = PublishSubject<String>() • Add data on the stream with onNext method nameSubject.onNext("Frederik") frederik jacques - @thenerd_be 30
31. PublishSubject let nameSubject = PublishSubject<String>() nameSubject.onNext("Frederik") nameSubject.subscribe(onNext: { (name) in print("Name = \(name)") }) nameSubject.onNext("Steven") frederik jacques - @thenerd_be 31
32. PublishSubject let nameSubject = PublishSubject<String>() nameSubject.subscribe(onNext: { (name) in print("Name = \(name)") }) nameSubject.onNext("Frederik") nameSubject.onNext("Steven") frederik jacques - @thenerd_be 32
33. BehaviorSubject • Subscribers get all upcoming events + the current value let nameSubject = BehaviorSubject<String>(value: "Frederik") • Add data on the stream with onNext method nameSubject.onNext("Steven") frederik jacques - @thenerd_be 33
34. BehaviorSubject let nameSubject = BehaviorSubject<String>(value: "Frederik") nameSubject.onNext("Steven") nameSubject.subscribe(onNext: { (name) in print("Name = \(name)") }) nameSubject.onNext("Spencer") frederik jacques - @thenerd_be 34
35. ReplaySubject • Subscribers get all upcoming events + the amount specified in the buffer from earlier events let nameSubject = ReplaySubject<String>.create(bufferSize: 2) • Add data on the stream with onNext method nameSubject.onNext("Frederik") frederik jacques - @thenerd_be 35
36. ReplaySubjects let nameSubject = ReplaySubject<String>.create(bufferSize: 1) nameSubject.onNext("Frederik") nameSubject.onNext("Steven") nameSubject.subscribe(onNext: { (name) in print("Name = \(name)") }) nameSubject.onNext("Spencer") frederik jacques - @thenerd_be 36
37. Disposebags frederik jacques - @thenerd_be 37
38. Disposebags A container in which your subscriptions are stored, so they don't get deallocated within the local scope of a function or get properly disposed when you class gets deallocated frederik jacques - @thenerd_be 38
39. Disposebags // Somewhere at the top private let disposeBag = DisposeBag() /////// // Somewhere else let nameSubject = ReplaySubject<String>.create(bufferSize: 1) nameSubject.onNext("Frederik") nameSubject.onNext("Steven") nameSubject.subscribe(onNext: { (name) in print("Name = \(name)") }).disposed(by: disposeBag) nameSubject.onNext("Spencer") frederik jacques - @thenerd_be 39
40. Sharing is caring frederik jacques - @thenerd_be 40
41. Sharing is caring • Every subscription, triggers the observable • Share an observable to avoid this (e.g. network requests) • share() • share(replay: 1, scope: .forever) • share(replay: 1, scope: .whileConnected) frederik jacques - @thenerd_be 41
42. Operators frederik jacques - @thenerd_be 42
43. Operators • Marble diagrams frederik jacques - @thenerd_be 43
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45. Filter • Filter out elements .filter({ (device) -> Bool in return device == "iPad" || device == "iPhone" }) frederik jacques - @thenerd_be 45
46. Map • Map from one thing to something else Observable.just( 18 ) .map { (age) -> String in guard age > 16 else { return "Not allowed to drink" } return "Allowed to drink" } frederik jacques - @thenerd_be 46
47. Take • Take x-number of elements from the start of the stream and complete frederik jacques - @thenerd_be 47
48. Skip • Skip x-number of elements before receiving elements on the stream frederik jacques - @thenerd_be 48
49. Distinct • Only allow unique elements in the stream • Use distinctUntilChanged if doubles are allowed, but not one after each other frederik jacques - @thenerd_be 49
50. Combining observables frederik jacques - @thenerd_be 50
51. CombineLatest • Combine 2 (or more) observables, but only if both have emitted at least one element frederik jacques - @thenerd_be 51
52. WithLatestFrom • Request the value of the last element of another stream frederik jacques - @thenerd_be 52
53. Debugging frederik jacques - @thenerd_be 53
54. Debugging Debugging is hard, the most encountered issues 1. it doesn't trigger 2. it triggers too much frederik jacques - @thenerd_be 54
55. Debugging • use debug() operator in the chain frederik jacques - @thenerd_be 55
56. Schedulers frederik jacques - @thenerd_be 56
57. Schedulers • Have nothing to do with threading • A context where a process takes place (can be a thread, dispatch_queue, NSOperation, ...). frederik jacques - @thenerd_be 57
58. Schedulers ObserveOn • Where does the code of the observer run • 99% of the cases, you'll be using this one frederik jacques - @thenerd_be 58
59. Schedulers SubscribeOn • Where does the code of the observable run frederik jacques - @thenerd_be 59
60. Unit Testing Quite easy to do • RxTest: Most code • RxBlocking: Block thread until you get result frederik jacques - @thenerd_be 60
61. RxSwift add-ons • RxCocoa • RxSwiftExt • RxDataSources • Check RxSwift Community for more! frederik jacques - @thenerd_be 61
62. Great resources • Slack Channel • RxSwift Book (Ray Wenderlich) • Marin Todorov's blog • Droids on roids blog • Rx.playground (in RxSwift GitHub repo) frederik jacques - @thenerd_be 62
63. Demo frederik jacques - @thenerd_be 63
64. Thank you frederik jacques - @thenerd_be 64
65. Q&A? frederik jacques - @thenerd_be 65