SWIFT & REACTIVEX Asynchronous Event-Based Funsies with RxSwift 

WHO I AM ➤ Aaron Douglas ➤ Milwaukee, WI USA ➤ Mobile Maker for Automattic (WordPress.com) ➤ Remote full time 3+ years ➤ @astralbodies 

REACTIVE?
 FUNCTIONAL?
 MEH? 

FUNCTIONAL & REACTIVE PROGRAMMING ➤ Reactive Programming ➤ Asynchronous Data Flow ➤ Functional Programming ➤ Map, Reduce, Filter ➤ Avoiding State ➤ Immutable Data ➤ Declarative Paradigm - logic of computation rather than describing flow ➤ Implementations - ReactiveCocoa/RAC, RxSwift 

WHAT IS RXSWIFT? 

WHAT IS RXSWIFT? ➤ Based on ReactiveX ➤ Many different ports: Java, JavaScript, .NET, Scala, Clojure, Swift, Kotlin, PHP , … ➤ Extends the Observer Pattern ➤ Related to Iterable Pattern ➤ Swift itself provides some protocols with equivalence ➤ SequenceType ➤ GeneratorType 

OBSERVER PATTERN 

NSNOTIFICATIONCENTER NSNotificationCenter .defaultCenter() .addObserver(self, selector:"downloadImage:", name: "BLDownloadImageNotification", object: nil) NSNotificationCenter .defaultCenter() .postNotificationName("BLDownloadImageNotification", object: self, userInfo: ["imageView": coverImage, "coverUrl": albumCover]) 

OBSERVER PATTERN 9 

ITERATOR PATTERN 

ITERATOR PATTERN 

GENERATORS, SEQUENCES, OH MY! 

GENERATORS public protocol GeneratorType { associatedtype Element public mutating func next() -> Self.Element? } 

GENERATORS class CountdownGenerator: GeneratorType { typealias Element = Int var element: Element init(array: [T]) { self.element = array.count } func next() -> Element? { guard element > 0 else { return nil } element -= 1 return element } } let xs = ["A", "B", "C"] let generator = CountdownGenerator(array: xs) while let i = generator.next() { print("Element \(i) of the array is \(xs[i])") } Element 2 of the array is C Element 1 of the array is B Element 0 of the array is A 

SEQUENCES public protocol SequenceType { associatedtype Generator : GeneratorType public func generate() -> Self.Generator } 

SEQUENCES class ReverseSequence: SequenceType { var array: [T] init(array: [T]) { self.array = array } func generate() -> CountdownGenerator { return CountdownGenerator(array: array) } } let reverseSequence = ReverseSequence(array: xs) let reverseGenerator = reverseSequence.generate() while let i = reverseGenerator.next() { print("Index \(i) is \(xs[i])") } for i in ReverseSequence(array: xs) { print("Index \(i) is \(xs[i])") } Index 2 is C Index 1 is B Index 0 is A Index 2 is C Index 1 is B Index 0 is A 

OBSERVABLES 

OBSERVERTYPE public protocol ObserverType { associatedtype E func on(event: Event) } public enum Event { case Next(Element) case Error(ErrorType) case Completed } 

OBSERVABLETYPE public protocol ObservableType : ObservableConvertibleType { associatedtype E func subscribe(observer: O) -> Disposable } public protocol ObservableConvertibleType { associatedtype E func asObservable() -> Observable } 

VISUALIZATIONS OF SEQUENCES --1--2--3--4--5--6--| // terminates normally --a--b--a--a--a---d---X // terminates with error ---tap-tap-------tap---> // infinite; never ends 

MAKING AN OBSERVABLE let disposeBag = DisposeBag() Observable.just("X") .subscribe { event in print(event) } .addDisposableTo(disposeBag) 

MAKING AN OBSERVABLE let disposeBag = DisposeBag() Observable.of("W", "X", "Y", "X") .subscribeNext { element in print(element) } .addDisposableTo(disposeBag) 

MAKING AN OBSERVABLE let disposeBag = DisposeBag() ["W", "X", "Y", "Z"].toObservable() .subscribeNext { print($0) } .addDisposableTo(disposeBag) 

SUBSCRIBING someObservable.subscribe( onNext: { print("Element: ", $0) }, onError: { print("Error: ", $0) }, onCompleted: { print("Completed") }, onDisposed: { print("Disposed") } ) someObservable .subscribeNext { print("Element: ", $0) } 

OPERATORS 

No content

MAP 

MAP let disposeBag = DisposeBag() Observable.of(1, 2, 3) .map { $0 * 10 } .subscribeNext { print($0) } .addDisposableTo(disposeBag) --- 10 20 30 

FILTER 

FILTER let disposeBag = DisposeBag() Observable.of(2, 30, 22, 5, 60, 1) .filter { $0 > 10 } .subscribeNext { print($0) } .addDisposableTo(disposeBag) --- 30 22 60 

SCAN 

SCAN let disposeBag = DisposeBag() Observable.of(1, 2, 3, 4, 5) .scan(0) { aggregateValue, newValue in aggregateValue + newValue } .subscribeNext { print($0) } .addDisposableTo(disposeBag) --- 1 3 6 10 15 

MERGE 

MERGE let disposeBag = DisposeBag() let subject1 = PublishSubject() let subject2 = PublishSubject() Observable.of(subject1, subject2) .merge() .subscribeNext { print($0) } .addDisposableTo(disposeBag) subject1.onNext("20") subject1.onNext("40") subject1.onNext("60") subject2.onNext("1") subject1.onNext("80") subject1.onNext("100") subject2.onNext("1") 20 40 60 1 80 100 1 

RXMARBLES.COM 

DISPOSING 

.dispose() 

.addDisposableTo(disposeBag) 

COCOA + RXSWIFT 

BINDINGS totCountStepper .rx_value .subscribeNext { value in self.totalNumberOfTots.value = Int(value) } .addDisposableTo(disposeBag) 

BINDINGS ➤ NSTextStorage ➤ UIActivityIndicatorView ➤ UIAlertAction ➤ UIApplication ➤ UIBarButtonItem ➤ UIButton ➤ UICollectionView ➤ UIControl ➤ UIDatePicker ➤ UIGestureRecognizer ➤ UIImagePickerController ➤ UIImageView ➤ UILabel ➤ UINavigationItem ➤ UIPageControl ➤ UIPickerView ➤ UIProgressView ➤ UIRefreshControl ➤ UIScrollView ➤ UISearchBar ➤ UISearchController ➤ UISegmentedControl ➤ UISlider ➤ UIStepper ➤ UISwitch ➤ UITabBar ➤ UITabBarItem ➤ UITableView ➤ UITextField ➤ UITextView ➤ UIView ➤ UIViewController 

AN EXAMPLE 

TATER TOT TIMER 

RXSWIFT IN THE WILD 

WHERE TO LEARN MORE 

WHERE TO LEARN MORE ➤ ReactiveX RxSwift main repo ➤ https://github.com/ReactiveX/RxSwift/ ➤ FRP iOS Learning Resources ➤ https://gist.github.com/JaviLorbada/4a7bd6129275ebefd5a6 ➤ Functional Reactive Programming with RxSwift ➤ https://realm.io/news/slug-max-alexander-functional-reactive-rxswift/ ➤ RxSwift Slack ➤ http://rxswift-slack.herokuapp.com/ 

AARON DOUGLAS @astralbodies http://astralbodi.es