Combine this!

The presentation is an overview of Combine framework for iOS development.

Transcript

1. Combine this! Maria Holubieva, iOS dev at Synergetica
3. Reactive programming is programming with asynchronous data streams that can be created, changed or combined on the go
4. Reactive programming is programming with asynchronous data streams that can be created, changed or combined on the go
5. Imperative programming UITextField we need to track text changing set textField delegate add realization of textField(_:shouldChangeCharactersIn:replacementString:) method in delegate wait until delegate method will be called
6. Reactive programming UITextField we need to track text changing UITextField H He Hel Hell Hello User Input produce a flow of User Input
7. Reactive programming UITextField we need to track text changing User Input H He Hel Hell Hello t
8. UITextField we need to track text changing subscribe to UITextFiled text change event Text Changed handle new Text Input Reactive programming
9. Combine
10. Publisher Subscriber
11. Publisher Subscriber delivers a sequence of values over time
12. Publisher Subscriber delivers a sequence of values over time subscribes to the publisher to receive its elements
13. Publisher Subscriber deliver a sequence of values over time subscribes to the publisher to receive its elements Observer Observable
14. Publisher Subscriber _ = Publishers.Just("Hello, world!”) _ = Publishers.Sequence<[Int], Never>(sequence: [1, 3, 6])
15. _ = Publishers.Just("Hello, world!”) _ = Publishers.Sequence<[Int], Never>(sequence: [1, 3, 6]) Publisher Subscriber Error type Sequence type
16. _ = Publishers.Just("Hello, world!”) _ = Publishers.Sequence<[Int], Never>(sequence: [1, 3, 6]) Publisher Subscriber enum Never {}
17. Publisher Subscriber _ = Publishers.Just("Hello, world!").sink { (value: String) in print(value) } _ = Publishers.Sequence<[Int], Never>(sequence: [1, 3, 6]) .sink { (value: Int) in print(value) }
18. Publisher Subscriber _ = Publishers.Just("Hello, world!").sink { (value: String) in print(value) } _ = Publishers.Sequence<[Int], Never>(sequence: [1, 3, 6]) .sink { (value: Int) in print(value) } OUTPUT: Hello, world! 1 3 6
19. Publisher Subscriber _ = Observable<String>.just("Hello, world!") .subscribe { (value: Event<String>) in print(value.element ?? "") } _ = Observable<Int>.of(1, 2, 3) .map({ return String($0) }) .subscribe { (value: Event<String>) in print(value.element ?? "") } OUTPUT: Hello, world! 1 2 3
20. Publisher Subscriber _ = Publishers.Just("Hello, world!") _ = Publishers.Sequence<[Int], Never>(sequence: [1, 3, 6]) class TextPrinter { let name: String init(name: String) { self.name = name } var text: String = "" { didSet { print(name+": "+text) } } }
21. Publisher Subscriber let printer1 = TextPrinter(name: "printer1") let printer2 = TextPrinter(name: "printer2") _ = Publishers.Just("Hello, world!").assign(to: \.text, on: printer1) _ = Publishers.Sequence<[Int], Never>(sequence: [1, 3, 6]) .map({ String($0) }) .assign(to: \TextPrinter.text, on: printer2) class TextPrinter { let name: String init(name: String) { self.name = name } var text: String = "" { didSet { print(name+": "+text) } } }
22. Publisher Subscriber let printer1 = TextPrinter(name: "printer1") let printer2 = TextPrinter(name: "printer2") _ = Publishers.Just("Hello, world!").assign(to: \.text, on: printer1) _ = Publishers.Sequence<[Int], Never>(sequence: [1, 3, 6]) .map({ String($0) }) .assign(to: \TextPrinter.text, on: printer2) class TextPrinter { let name: String init(name: String) { self.name = name } var text: String = "" { didSet { print(name+": "+text) } } } OUTPUT: printer1: Hello, world! printer2: 1 printer2: 3 printer2: 6
23. Publisher Subscriber let printer1 = TextPrinter(name: “printer1") _ = Observable<Int>.of(1, 2, 3) .map({ return String($0) }) .bind(to: printer1.rx.text) extension TextPrinter: ReactiveCompatible { } extension Reactive where Base: TextPrinter { internal var text: Binder<String> { return Binder(self.base) { printer, text in printer.text = text } } }
24. Publisher Subscriber let printer1 = TextPrinter(name: "printer1") let printer2 = TextPrinter(name: "printer2") let publisher1 = Publishers.Just("Hello, world!") let publisher2 = Publishers.Sequence<[Int], Never>(sequence: [1, 3, 6]) .map({ String($0) }) let subscriber1 = Subscribers.Assign(object: printer1, keyPath: \.text) let subscriber2 = Subscribers.Assign(object: printer2, keyPath: \.text) publisher1.subscribe(subscriber1) publisher2.subscribe(subscriber2) class TextPrinter { let name: String init(name: String) { self.name = name } var text: String = "" { didSet { print(name+": "+text) } } }
25. let printer1 = TextPrinter(name: "printer1") let printer2 = TextPrinter(name: "printer2") let publisher1 = Publishers.Just("Hello, world!") let publisher2 = Publishers.Sequence<[Int], Never>(sequence: [1, 3, 6]) .map({ String($0) }) let subscriber1 = Subscribers.Assign(object: printer1, keyPath: \.text) let subscriber2 = Subscribers.Assign(object: printer2, keyPath: \.text) publisher1.subscribe(subscriber1) publisher2.subscribe(subscriber2) Publisher Subscriber class TextPrinter { let name: String init(name: String) { self.name = name } var text: String = "" { didSet { print(name+": "+text) } } } OUTPUT: printer1: Hello, world! printer2: 1 printer2: 3 printer2: 6
26. @Published
27. class LoginViewController: UIViewController, UITextFieldDelegate { @IBOutlet weak var btnSignIn: UIButton! private var btnSignInEnabledPublisher: AnyCancellable? private lazy var viewModel: LoginViewModel = { return LoginViewModel() }() override func viewDidLoad() { super.viewDidLoad() btnSignInEnabledPublisher = viewModel.$loginState .map({ return $0 == .signInEnabled }) .assign(to: \.isEnabled, on: btnSignIn) } ... } @Published class LoginViewModel { @Published private(set) var loginState: LoginState = .signInDisabled { didSet { switch loginState { case .signInDisabled: break case .signInEnabled: break case .signInStarted: performSignInRequest() } } } ... }
28. AnyCancellable class calls cancel() on deinit and makes sure subscriptions terminate early Combine Memory Management
29. What is @Published?
30. What is @Published? It’s a property wrapper
31. What is @Published? It’s a property wrapper But what is property wrapper?
32. is a generic data structure that encapsulates read/write access to a property while adding some extra behaviour to “augment” its semantics. Property wrapper
33. Property wrapper example @propertyWrapper struct UUIDIdetified<Value> { let id = UUID() var wrappedValue: Value init(wrappedValue: Value) { self.wrappedValue = wrappedValue } } @UUIDIdetified var text = "Some Text” print($text.id) OUTPUT: 70665FD5-AFA5-466F-96BB-3DD9611D0D32
34. Property wrapper example @propertyWrapper struct UserDefault<T> { let key: String let defaultValue: T init(_ key: String, defaultValue: T) { self.key = key self.defaultValue = defaultValue } var wrappedValue: T { get { return UserDefaults.standard.object(forKey: key) as? T ?? defaultValue } set { UserDefaults.standard.set(newValue, forKey: key) } } } @UserDefault("has_seen_app_introduction", defaultValue: false) var isHasSeenAppIntro: Bool
35. If you want to cancel a subscription you can do that by calling dispose on it. You can also add the subscription to a DisposeBag which will cancel the subscription for you automatically on deinit of the DisposeBag Instance. RxSwift Memory Management
36. No something like DisposeBag in Combine private var emailPublisher: AnyCancellable? private var emailEditablePublisher: AnyCancellable? private var passwordPublisher: AnyCancellable? private var passwordEditablePublisher: AnyCancellable? private var btnSignInEnabledPublisher: AnyCancellable?
37. More in Combine
38. Subjects
39. Subjects in Combine are basically publishers on which we can subscribe but also dynamically send events to them.
40. Subjects in Combine are basically publishers on which we can subscribe but also dynamically send events to them. PassthroughSubject CurrentValueSubject
41. PassthroughSubject example let subject = PassthroughSubject<String, Never>() let publisher = subject.eraseToAnyPublisher() let subscriber1 = publisher.sink(receiveValue: { value in print(value) }) //subscriber1 will recive the events but not the subscriber2 subject.send("Event1") subject.send("Event2") let subscriber2 = publisher.sink(receiveValue: { value in print(value) }) //Subscriber1 and Subscriber2 will recive this event subject.send("Event3") OUTPUT: Event1 Event2 Event3 Event3
42. RxSwift Subjects PublishSubject BehaviourSubject ReplaySubject Variable CurrentValueSubject PassthroughSubject
43. Schedulers
44. Schedulers let selectedFilter = PassthroughSubject<String, Never>() let searchText = NotificationCenter.default .publisher(for: UITextField.textDidChangeNotification, object: textFieldEmail) .map( { ($0.object as! UITextField).text } ) .debounce(for: .milliseconds(500), scheduler: RunLoop.main) .eraseToAnyPublisher() let publisher = Publishers.CombineLatest(selectedFilter, searchText) .map({ (selectedFilter, searchText) in "\(selectedFilter) \(searchText)" }) _ = publisher.sink { value in print(value) }
45. RxSwift Schedulers let publish1 = PublishSubject<Int>() let publish2 = PublishSubject<Int>() let concurrentScheduler = ConcurrentDispatchQueueScheduler(qos: .background) Observable.of(publish1, publish2) .observeOn(concurrentScheduler) .merge() .subscribeOn(MainScheduler()) .subscribe(onNext:{ print($0) }) publish1.onNext(20) publish1.onNext(40) OUTPUT: 20 40
46. Operators
47. Transforming: map _ = Publishers.Sequence(sequence: [1,2,4]) .map { $0 * 10 } .sink(receiveValue: { print($0) })
48. Filtering: filter _ = Publishers.Sequence(sequence: [1,2,2,3,3,4,7]) .map { $0 * 2 } .filter { $0.isMultiple(of: 2) } .dropFirst(3) .removeDuplicates() .sink(receiveValue: { value in print(value) })
49. Combining: merge let germanCities = PassthroughSubject<String, Never>() let italianCities = PassthroughSubject<String, Never>() let europianCities = Publishers.Merge(germanCities, italianCities) _ = europianCities.sink(receiveValue: { city in print("\(city) is a city in europe") })
50. Combining: combine Latest let selectedFilter = PassthroughSubject<String, Never>() let searchText = PassthroughSubject<String, Never>() let publisher = Publishers.CombineLatest(selectedFilter, searchText) .sink { (selectedFilter, searchText) in "\(selectedFilter) \(searchText)" }
51. And others…
52. Conclusions
53. Conclusions Combine is available since iOS13 Combine is faster than RxSwift RxSwift has more operators and other abilities… yet RxSwift has big community MVVM is coming!
54. Small sample
55. Thanks for your attention!
56. Useful links https://codepen.io/HunorMarton/post/imperative-vs-reactive https://medium.com/flawless-app-stories/problem-solving- with-combine-swift-4751885fda77 https://www.avanderlee.com/swift/property-wrappers/ https://nshipster.com/never/ https://ruicosta.net/2019/06/30/Swift-MVVM-and- Combine.html