This is an introduction to reactive concepts using Swift specifically with ReactiveX’s implementation, RxSwift. ReactiveX is an API for asynchronous programming with observable streams originally implemented with .NET and LINQ. ReactiveX is a combination of the best ideas from the Observer pattern, the Iterator pattern, and functional programming. You’ll learn about all the basic moving parts of RxSwift and why you want to use it in your application. Original presented 23-Aug-2016 at 360iDev 2016 - Denver, CO.

1. SWIFT & REACTIVEX
Asynchronous Event-Based Funsies with RxSwift

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

3. REACTIVE?
FUNCTIONAL?
MEH?

4. 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

5. WHAT IS RXSWIFT?

6. 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

7. OBSERVER PATTERN

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

9. OBSERVER PATTERN
9

10. ITERATOR PATTERN

11. ITERATOR PATTERN

12. GENERATORS, SEQUENCES,
OH MY!

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

14. GENERATORS
class CountdownGenerator: GeneratorType {
typealias Element = Int
var element: Element
init<T>(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

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

16. SEQUENCES
class ReverseSequence<T>: 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

17. OBSERVABLES

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

19. OBSERVABLETYPE
public protocol ObservableType : ObservableConvertibleType {
associatedtype E
func subscribe<O: ObserverType where O.E == E>(observer: O) -> Disposable
}
public protocol ObservableConvertibleType {
associatedtype E
func asObservable() -> Observable<E>
}

20. 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

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

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

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

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

25. OPERATORS

27. MAP

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

29. FILTER

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

31. SCAN

32. 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

33. MERGE

34. MERGE
let disposeBag = DisposeBag()
let subject1 = PublishSubject<String>()
let subject2 = PublishSubject<String>()
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

35. RXMARBLES.COM

36. DISPOSING

37. .dispose()

38. .addDisposableTo(disposeBag)

39. COCOA + RXSWIFT

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

41. 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

42. AN EXAMPLE

43. TATER TOT TIMER

44. RXSWIFT IN THE WILD

45. WHERE TO LEARN MORE

46. 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/

47. AARON DOUGLAS@astralbodies
http://astralbodi.es