Introduction to RxSwift

This was a presentation I gave at CocoaHeads Johannesburg about RxSwift

Transcript

1. Introduction to
   RxSwift
   Peter-John Welcome
   @pjapplez
   Mobile Engineering Lead
   

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2. About me
   

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4. What is Rx(ReactiveX)?
   

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5. What is Rx:
   ReactiveX is an API for asynchronous
   programming with observable streams
   Observable streams (i.e. streams that
   can be observed) in the context of
   Reactive Extensions are like event
   emitters that emit 3 events: next,
   error, and complete.
   

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7. What brought this on?
   

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8. History
   ● Started as part of the .NET/C# ecosystem
   ● Reactive programming is a programming paradigm
   oriented around data flows and the propagation of
   change
   ● Functional Programming
   

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9. Let’s get into RxSwift
   

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10. Observables and Observers:
    ● An Observable is something which emits notifications of
    change.
    ● An Observer is something which subscribes to an
    Observable, in order to be notified when it has changed.
    

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11. Observables and Observers:
    ● .next(value: T) — When a value or collection of values is added
    to an observable sequence
    ● .error(error: Error) — If an Error is encountered, a sequence
    will emit an error event. This will also terminate the sequence.
    ● .completed — If a sequence ends normally it sends a completed
    event to its subscribers
    

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12. Dispose Bag:
    ● RxSwift and RxCocoa also have an additional tool to help deal
    with ARC and memory management: the DisposeBag. Helps with
    deallocation of object.
    

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13. let observable = Observable.just("Hello World")
    observable.subscribe(onNext: {
    myString in
    print(myString)
    }).addDisposableTo(disposeBag)
    Observables and Observers:
    

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15. Subjects:
    ● PublishSubject — If you subscribe to it you will get all the events that
    will happen after you subscribed.
    ● BehaviourSubject — A behavior subject will give any subscriber the most
    recent element and everything that is emitted
    ● ReplaySubject — you can define how many recent items you want to emit to
    new subscribers
    

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16. Subjects:
    let bag = DisposeBag()
    var publishSubject = PublishSubject()
    publishSubject.onNext("Hello")
    publishSubject.subscribe(onNext:{
    print($0)
    }).addDisposableTo(bag)
    

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17. Transformations (functional
    programming)
    

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18. Transformation:
    ● map 
    ● flatMap 
    ● Scan 
    ● Filter
    ● Zip
    ● Many More
    

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19. Observable.of(1,2,3,4).map {
    return $0 * 10
    }.subscribe(onNext:{
    print($0)
    })
    OUTPUT: 10, 20, 30, 40
    Transformation: map
    

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20. let a = Observable.of(1,2,3,4,5)
    let b = Observable.of("a","b","c","d")
    Observable.zip(a,b){ return ($0,$1) }.subscribe {
    print($0)
    }
    OUTPUT: [(1, "a"), (2, "b"), (3, "c"), (4, "d")]
    Transformation: zip
    

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21. Schedulers
    

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22. Schedulers:
    ● All operators and observables run on the same thread that they
    are subscribed on.
    ● We can force them on different threads with subscribeOn and
    observeOn.
    ● It uses operation-ques and dispatch-queues under the hood.
    

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23. Schedulers:
    ● MainScheduler
    ● CurrentThreadScheduler
    ● SerialDispatchQueueScheduler
    ● ConcurrentDispatchQueueScheduler
    ● OperationQueueScheduler
    

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24. let publish = PublishSubject()
    let concurrentScheduler = ConcurrentDispatchQueueScheduler(qos:
    .background)
    Observable.of(publish)
    .observeOn(concurrentScheduler)
    .subscribeOn(MainScheduler())
    .subscribe(onNext:{
    print($0)
    })
    publish.onNext(20)
    publish.onNext(40)
    OUTPUT: 20 40
    Schedulers:
    

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25. RxCocoa
    

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26. searchbar.rx.text.bind(to: viewModel.query).disposed(by:
    disposeBag)
    searchbar.rx.searchButtonClicked.asDriver(onErrorJustReturn: ())
    .drive(onNext: { [weak self] _ in
    self?.viewModel.retrieveStuff()
    }).disposed(by: disposeBag)
    searchbar.rx.cancelButtonClicked
    .map{ _ in "" }
    .bind(to: viewModel.query)
    .disposed(by: disposeBag)
    RxCocoa:
    

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27. Demo Time
    

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29. Unit Testing
    

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31. func testStuff() {
    let dummyData = dummylist()
    let events = [
    next(0, dummyData)
    ]
    let scheduler = TestScheduler(initialClock: 0)
    let inputObservable =
    scheduler.createHotObservable(events).asObservable()
    let outputObserver =
    scheduler.createObserver(Array.self)
    let systemUnderTest = ViewModel()
    systemUnderTest.query.value = ""
    }
    Unit Testing: Setup
    

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32. func testStuff() {
    .....
    stub(someRepoMock) { mock in
    when(mock.searchForNames(r:any())).thenReturn(inputObservable)
    }
    _ = systemUnderTest.results.subscribe(outputObserver)
    scheduler.start()
    systemUnderTest.retrieveStuff()
    verify(someRepoMock , times(1)).searchForNames(r: any())
    }
    }
    Unit Testing: execution
    

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33. Resources:
    ● https://www.thedroidsonroids.com/blog/ios/rxswift-by-examples-1-t
    he-basics/
    ● https://github.com/ReactiveX/RxSwift
    ● https://medium.com/ios-os-x-development/learn-and-master-%EF%B8%8
    F-the-basics-of-rxswift-in-10-minutes-818ea6e0a05b
    ● https://www.raywenderlich.com/900-getting-started-with-rxswift-an
    d-rxcocoa
    ● https://en.wikipedia.org/wiki/Reactive_extensions
    

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34. Thanks!
    Contact me:
    https://medium.com/@pjwelcome
    @pjapplez
    pjwelcome@gmail.com
    Peter-johnwelcome.co.za
    https://github.com/pjwelcome
    

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