Combine Overview CombineΰϦΰϦΩϟονΞοϓձ Daiki Matsudate @d_date iOS Developer

Daiki Matsudate • Tokyo, Japan • iOS Developer from iOS 4 • Independent Developer • @d_date • Sushi

March, 18 - 20th, 2020 https://www.tryswift.co/

A unified, declarative API for 
 processing values over time

Why Reactive Programing?

Why Reactive Programing? • ෳ਺ͷඇಉظ (Asynchronous) ͳλεΫΛͲ͏ѻ͏͔ • Ͳ͏ѻ͏͔ • Ͳͷॱ൪Ͱʁ • ௚ྻ / ฒྻ? • ్தͰΤϥʔ͕ൃੜͨ͠Βʁ

Reactive Programing

Reactive Programming • Observer Pattern • ΠϕϯτͷൃՐΛϋϯυϦϯά͍ͨ͠ͱ͜ΖͰ؂ࢹ͢Δ • Operators • ΠϕϯτΛՃ޻͢Δ • Open Source • RxSwift / Reactive Swift

https://twitter.com/diegopetrucci/status/1135655480825655297

Combine

Combine • Declarative Swift API • ඇಉظͳΠϕϯτΛܕͱͯ͠දݱ • ଟछଟ༷ͳԋࢉࢠͰΠϕϯτΛϋϯυϦϯά • Reactive Framework by Apple

Publisher

Publisher • Value΍ErrorΛੜ੒͢Δ • ొ࿥͞ΕͨSubscriberʹValue΍ErrorΛૹ৴͢Δ

public protocol Publisher { /// The kind of values published by this publisher. associatedtype Output /// The kind of errors this publisher might publish. /// Use `Never` if this `Publisher` does not publish errors. associatedtype Failure : Error /// This function is called to attach the specified `Subscriber` to this `Publisher` by `subscribe(_:)` func receive(subscriber: S) where S : Subscriber, Self.Failure == S.Failure, Self.Output == S.Input } Publisher

@Published @propertyWrapper public struct Published { /// Initialize the storage of the Published property as well as the corresponding `Publisher`. public init(initialValue: Value) public class Publisher : Publisher { /// The kind of values published by this publisher. public typealias Output = Value /// The kind of errors this publisher might publish. /// /// Use `Never` if this `Publisher` does not publish errors. public typealias Failure = Never /// This function is called to attach the specified `Subscriber` to this `Publisher` by `subscribe(_:)` public func receive(subscriber: S) where Value == S.Input, S : Subscriber, S.Failure == Published.Publisher.Failure } /// The property that can be accessed with the `$` syntax and allows access to the `Publisher` public var projectedValue: Published.Publisher { mutating get } }

Default Publishers • Notification Center • URLSession • Just, Future • CurrentValueSubject, PassthroughSubject • NSManagedObject let ncpublisher = NotificationCenter.Publisher(center: .default, name: .NSCalendarDayChanged) let sessionPublisher = URLSession(configuration: .default) .dataTaskPublisher(for: URL(string: “https://api.google.com")!) let managedObject = NSManagedObject(context: context).publisher(for: \.hasChanges) let just = Just("") let future = Future { (result) in result(.success("result")) result(.failure(TypedError.example)) }

From WWDC19 Introducing Combine One Many Synchronous Asynchronous Int Array Future Publisher

Subscriber

Publisher • Publisher͕ൃߦͨ͠஋΍Error, completionΛߪಡ͢Δ • ߪಡΛΩϟϯηϧͰ͖ΔʢCancellable)

public protocol Subscriber : CustomCombineIdentifierConvertible { /// The kind of values this subscriber receives. associatedtype Input /// The kind of errors this subscriber might receive. /// Use `Never` if this `Subscriber` cannot receive errors. associatedtype Failure : Error /// Tells the subscriber that it has successfully subscribed to the publisher and may request items. /// /// Use the received `Subscription` to request items from the publisher. func receive(subscription: Subscription) /// Tells the subscriber that the publisher has produced an element. func receive(_ input: Self.Input) -> Subscribers.Demand /// Tells the subscriber that the publisher has completed publishing, either normally or with an error. func receive(completion: Subscribers.Completion) } Subscriber

Assign

let labelTextSubscriber = Subscribers.Assign(object: label, keyPath: \.text) $queryPublisher .map { "searching for \($0)..." } .map(Optional.init) .subscribe(labelTextSubscriber) labelTextSubscriber.cancel() Assign

let cancellable = $queryPublisher .map { "searching for \($0)..." } .assign(to: \.text, on: label) // how to cancel cancellable.cancel() Assign

var cancellables = [AnyCancellable]() $queryPublisher .map { "searching for \($0)..." } .assign(to: \.text, on: label) .store(in: &cancellables) Assign

Sink

let labelTextSubscriber = Subscribers.Sink(receiveCompletion: { _ in }) { self.label.text = $0 } $queryPublisher .map { "searching for \($0)..." } .subscribe(labelTextSubscriber) labelTextSubscriber.cancel() Sink

let cancellable = $queryPublisher .map { "searching for \($0)..." } .sink { self.label.text = $0 } cancellable.cancel() Sink

var cancellables = [AnyCancellable]() $queryPublisher .map { "searching for \($0)..." } .sink { self.label.text = $0 } .store(in: &cancellables) Sink

subscribe(on:) vs. receive(on:)

subscribe(on:) vs. receive(on:) • subscribe(on:) ͸ upstream messagesʹӨڹ • receive(on:) ͸downstream messagesͷ࣮ߦίϯςΩετʹӨڹ • ͜ͷྫͰ͸ɺpublisher΁ͷϦΫΤετ͸backgroundQueueͰߦΘΕΔ ͕ɺΤϨϝϯτΛड͚औΔͷ͸ϝΠϯεϨου let backgroundQueue = DispatchQueue(label: "background", qos: .utility) $queryPublisher .map { "searching for \($0)..." } .subscribe(on: backgroundQueue) .receive(on: DispatchQueue.main) .sink { self.label.text = $0 } .store(in: &cancellables)

The Pattern Subscriber is attached to Publisher Publisher sends a Subscription Subscriber requests N values Publisher sends N values or less Publisher sends completion Publisher Subscriber subscribe( ) receive(subscription:) request(_ : Demand) receive(completion:) receive(_ : Input) receive(_ : Input) • • •

Subject

Subject • PublisherͱSubscriberͷ྆ํͷੑ࣭Λ΋ͭ • ෳ਺ͷSubscriber΁஋ΛϒϩʔυΩϟετ͢Δ

Kinds of Subjects Passthrough CurrentValue

Kinds of Subjects Passthrough CurrentValue

Binding to SwiftUI

// Combine with SwiftUI class WizardModel : BindableObject { var trick: WizardTrick { didSet { didChange.send() } var wand: Wand? { didSet { didChange.send() } let didChange = PassthroughSubject() } struct TrickView: View { @ObjectBinding var model: WizardModel var body: some View { Text(model.trick.name) } }

Operator

catch abortOnError allSatisfy append breakpoint breakpointOnError combineLatest compactMap count dropFirst filter first handleEvents ignoreOutput last log mapError max min output prefix prepend print removeDuplicates replaceEmpty replaceError replaceNil retry scan setFailureType switchToLatest zip map contains flatMap reduce merge drop collect From WWDC19 Introducing Combine

Error Handling

Failure Handling Operators assertNoFailure retry catch mapError setFailureType

https://github.com/freak4pc/rxswift-to-combine-cheatsheet/blob/master/Data/core_components.csv RxSwift to Combine

WWDC Sessions Introducing Combine WWDC19 Combine in Practice WWDC19 Data Flow through SwiftUI WWDC19

Great Presentations • https://speakerdeck.com/riteshhh/combine-all-the-things