RxSwift: an elegant weapon for a statically typed age

Reactive Extensions are hardly a new concept, but it took some time to enter mainstream iOS development. For all of you wondering "is it worth the hype", here comes the RxSwift primer. We'll learn what the Observable is all about and how to use it without shooting ourselves in the foot. Why would you want to incorporate RxSwift into your project? Come and see!

Transcript

1. RXSWIFT
   AN ELEGANT WEAPON
   FOR A STATICALLY-TYPED AGE
   BY KRZYSZTOF SIEJKOWSKI
   

   View Slide

2. ✨
   WHAT'S RXSWIFT?
   

   View Slide

3. REACTIVE EXTENSIONS
   

   View Slide

4. OBSERVABLE GIVES DATA
   OBSERVER TAKES DATA
   

   View Slide

5. DATA ➡ NEXT[VALUE]* (COMPLETED | ERROR)
   Next("3"), Next("2"), Next("1"), Next("!"), Completed
   Next("The Spanish Inquisition"), Error(NobodyExpects)
   Error(RequestTimeout)
   Completed
   

   View Slide

6. public enum Event {
   case Next(Element)
   case Error(ErrorType)
   case Completed
   }
   protocol ObserverType {
   associatedtype Element
   }
   protocol ObservableType {
   associatedtype Element
   }
   

   View Slide

7. "a combination of the best ideas
   from
   the Observer pattern,
   the Iterator pattern,
   and functional programming"
   — reactivex.io
   

   View Slide

8. FROM OBSERVER PATTERN
   let notificationCenter : NSNotificationCenter
   notificationCenter.addObserverForName("ButtonTapped",
   object: nil, queue: nil) { (notification: NSNotification) in
   // observer closure
   }
   let observable: Observable
   observable.subscribeNext { (event: ButtonTappedEvent) in
   // observer closure
   }
   

   View Slide

9. FROM ITERATOR PATTERN
   let generator = [1, 2, 3, 4, 5, 6].generate()
   while let elem = generator.next() {
   // elem is pulled from sequence
   }
   let observer = AnyObserver { event in
   // event is pushed by observable
   }
   [1, 2, 3, 4, 5, 6].asObservable().subscribe(observer)
   

   View Slide

10. FROM FUNCTIONAL PROGRAMMING
    [1, 2, 3, 4, 5, 6].filter { ... }
    .map { ... }
    .flatMap { ... }
    [1, 2, 3, 4, 5, 6].asObservable()
    .filter { ... }
    .map { ... }
    .flatMap { ... }
    

    View Slide

11. OBSERVABLE
    PUBLISHES AND
    TRANSFORMS EVENTS
    OBSERVER
    RECEIVES EVENTS
    

    View Slide

12. THE REST IS
    UP TO YOU
    

    View Slide

13. PROTOCOL
    UIVIEW
    OBSERVABLE
    

    View Slide

14. ✨
    HOW TO USE RXSWIFT?
    

    View Slide

15. OPERATORS
    

    View Slide

16. REACTIVEX.IO/DOCUMENTATION/
    OPERATORS.HTML
    GITHUB.COM/REACTIVEX/RXSWIFT/BLOB/
    MASTER/DOCUMENTATION/API.MD
    

    View Slide

17. CREATE FROM EXISTING OBJECT
    ["Mobile", "Warsaw"].asObservable()
    textField.rx_text.asObservable()
    NSURLSession.sharedSession().rx_JSON(request)
    

    View Slide

18. CREATE WITH HELPER FUNCTIONS
    Observable.interval(1, scheduler: MainScheduler.instance)
    Observable.repeatElement("Did you miss me?")
    Observable.error(CouldHaveGoneBetter())
    let v = Variable("Riding to Valhalla")
    v.asObservable()
    v.value = "Witness me!"
    

    View Slide

19. CREATE WITH CUSTOM LOGIC
    Observable.create { observer in
    observer.onNext("keep calm")
    observer.onNext("and")
    observer.onNext("stay observable")
    observer.onCompleted()
    return NopDisposable.instance
    }
    ONLY ON VERY SPECIAL OCCASIONS
    

    View Slide

20. COMBINE: RXMARBLES.COM
    observable.concat(secondObservable)
    Observable.combineLatest(observable1, observable2, observable3) {
    elem1, elem2, elem3 in elem1 + elem2 + elem3
    }
    Observable.zip(observable1, observable2) {
    elem1, elem2 in (elem1, elem2)
    }
    

    View Slide

21. PERFORM WORK IN DATA PIPES
    observable
    .distinctUntilChanged()
    .filter { elem in
    elem > 0
    }
    .map { [weak self] elem in
    self?.performWork(elem)
    }
    .flatMap { [weak self] elem in
    self?.useForAsyncOperation(elem)
    }
    

    View Slide

22. CONNECT EVENT STREAM TO YOUR LOGIC
    observable.subscribeNext { [weak self] elem in
    self?.processValue(elem)
    }
    observable.asDriver(onErrorJustReturn: "sorry!")
    .drive(label.rx_text)
    

    View Slide

23. RECAP
    > observable ➡ events ➡ observer
    > observer ❤ iterator ❤ functional programming
    > customizable building block "
    > operators #
    

    View Slide

24. !
    DON'T SHOOT YOURSELF
    IN THE FOOT
    

    View Slide

25. Any sufficiently advanced technology is
    indistinguishable from magic.
    — Arthur C. Clarke
    BUT IT'S NOT MAGIC!
    

    View Slide

26. !
    MEMORY
    MANAGEMENT
    

    View Slide

27. USER-GENERATED EVENTS
    let disposeBag = DisposeBag()
    let gestureRecognizer = UITapGestureRecognizer()
    gestureRecognizer.rx_event
    .subscribeNext { [weak self] _ in
    self?.processDetectedTap()
    }
    .addDisposableTo(disposeBag)
    view.addGestureRecognizer(gestureRecognizer)
    

    View Slide

28. CLEAN UP!
    let disposeBag = DisposeBag()
    let subscription = observable.subscribe(observer)
    subscription.addDisposableTo(disposeBag)
    ...
    disposeBag = nil
    

    View Slide

29. WEAKIFY SELF IN CLOSURES
    class SomeClass {
    func someMethod(param: Int) { ... }
    func otherMethod -> Observable {
    return observable.just(1)
    .map(someMethod)
    }
    }
    return observable.just(1).map { [weak self] elem in
    self?.someMethod(elem) ?? 42
    }
    

    View Slide

30. !
    ASYNCHRONOUS
    EXECUTION
    

    View Slide

31. NETWORK CALL
    class NetworkClient {
    func fetchSomeNews() -> Observable {
    return NSURLSession.sharedSession()
    .rx_JSON("https://my.server.com/api/v2/news")
    .observeOn(SerializationScheduler.instance)
    .map { [weak self] json in
    self?.newsDeserializer.deserialize(json)
    }
    }
    }
    

    View Slide

32. NETWORK CALL
    self.networkClient.fetchSomeNews()
    .observeOn(MainScheduler.instance)
    .subscribeNext { [weak self] news in
    self?.newsView.presentNews(news)
    }
    .addDisposableTo(disposeBag)
    

    View Slide

33. OBSERVABLE
    IS SINGLE-THREADED
    

    View Slide

34. DECLARATION THREAD
    subscribe
    GENERATION THREAD
    subscribeOn & CREATE METHODS
    WORK THREAD(S)
    observeOn
    

    View Slide

35. 1. Declaration thread until told otherwise.
    2. Generation thread until changed.
    3. Only first generation thread change counts.
    4. No limit on work thread changes.
    

    View Slide

36. !
    STATE
    

    View Slide

37. MODEL-UI BINDING
    class MyViewController {
    func bindUserData() {
    let observable = self.userService.provideUserName()
    .observeOn(MainScheduler.instance)
    .shareReplay(1)
    observable.bindTo(self.userDataLabel.rx_text)
    .addDisposableTo(self.disposeBag)
    observable.subscribeNext { [weak self] userName in
    self?.navigationItem.title = userName
    }.addDisposableTo(self.disposeBag)
    }
    }
    

    View Slide

38. OBSERVABLE DOESN'T REMEMBER EVENTS
    let observable = Observable.just(1)
    .map { _ in print("I'm in map!") }
    observable.subscribeNext { _ in print("first") }
    observable.subscribeNext { _ in print("second") }
    // I'm in map!
    // first
    // I'm in map
    // second
    

    View Slide

39. UNTIL EXPLICITLY TOLD SO
    let observable = Observable.just(1)
    .map { _ in print("I'm in map!") }
    .shareReplay(1)
    observable.subscribeNext { _ in print("first") }
    observable.subscribeNext { _ in print("second") }
    // I'm in map!
    // first
    // second
    

    View Slide

40. !
    READABILITY
    

    View Slide

41. almost every single developer
    that I talked to uses strong and
    inflammatory language about its
    unreadability.
    — Brent Simmons, Reactive Followup
    

    View Slide

42. EXTRACT LOGIC
    NSURLSession.sharedSession().rx_response(myNSURLRequest)
    .flatMap { (data: NSData!, response: NSURLResponse!) -> Observable in
    guard let response = response as? NSHTTPURLResponse
    else { return Observable.error(yourNSError) }
    if 200 ..< 300 ~= response.statusCode {
    return just(transform(data))
    } else {
    return Observable.error(yourNSError)
    }
    }
    NSURLSession.sharedSession().rx_response(myNSURLRequest)
    .flatMap { [weak self] data, response in self?.processResponse(data, response) }
    

    View Slide

43. USE PROVIDED HELPERS
    AND CREATE YOUR OWN
    observable.just("they see me rollin'")
    .catchError { _ in Observable.empty() }
    .observeOn(MainScheduler.instance)
    .shareReplayLatestWhileConnected()
    observable.just("they hatin'")
    .asDriver { _ in Driver.empty() }
    

    View Slide

44. RECAP
    > manage memory !
    > identify the threads "
    > know when to share work #
    > good practices apply! $
    

    View Slide

45. !
    ALL THINGS OBSERVABLE
    

    View Slide

46. OBSERVABLES SCALE
    > for networking?
    > for asynchronous operations?
    > for updating model and driving ui?
    > for communication between layers?
    > for all logic?
    

    View Slide

47. OBSERVABLES EXPRESS DATA FLOW
    fetchDataFromServer()
    .observeOn(BackgroundScheduler.instance)
    .map { deserializeFromJson() }
    .flatMap { decideOnCaching() }
    .map { performComputation() }
    .flatMap { updateModel() }
    .asDriver { _ in provideDefaultValue() }
    .driveNext { updateUI() }
    Advanced iOS Application Architecture and Patterns
    

    View Slide

48. OBSERVABLES REPLACE
    func optionalToObservable(optional: T?) -> Observable {
    return Observable.just(optional).flatMap { elem -> Observable in
    if let optional = optional { return Observable.just(optional) }
    else { return Observable.error(NilError()) }
    }
    }
    optional, result, future, throws, sequencetype, ...
    KVO, NSNotificationCenter, target-action, callbacks,
    GCD, ...
    

    View Slide

49. OBSERVABLES UNIFORM
    func fun(observable: Observable) -> Observable
    init(
    dataObservable: Observable,
    dataObserver: E
    ) { ... }
    

    View Slide

50. SWIFTY id
    

    View Slide

51. LEARN ONCE, WRITE EVERYWHERE
    > ReactiveCocoa / Interstellar
    > RxJava / RxKotlin / RxGroovy
    > RxScala / RxClojure
    > RxPy / Rx.rb / RxJRuby
    > RxCpp / Rx.NET / UniRx
    > RxJS / Elm
    

    View Slide

52. DEVELOPER FRIENDLY
    guides at guides.rxswift.org
    docs at reactivex.io
    source at github.com/ReactiveX/RxSwift
    extensions at community.rxswift.org
    community at slack.rxswift.org
    

    View Slide

53. RECAP
    > use a little or a lot !
    > uniform various concepts "
    > express data flow #
    > check the docs $
    > consult the community %
    

    View Slide

54. THANK YOU!
    QUESTIONS?
    

    View Slide