A collection of Rx operators & tools not found in the core RxSwift distribution
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RxSwiftExt

If you're using RxSwift, you may have encountered situations where the built-in operators do not bring the exact functionality you want. The RxSwift core is being intentionally kept as compact as possible to avoid bloat. This repository's purpose is to provide additional convenience operators and Reactive Extensions.

Installation

This branch of RxSwiftExt targets Swift 4.x and RxSwift 4.0.0 or later.

  • If you're looking for the Swift 3 version of RxSwiftExt, please use version 2.5.1 of the framework.
  • If your project is running on Swift 2.x, please use version 1.2 of the framework.

CocoaPods

Using Swift 4:

pod "RxSwiftExt"

Using Swift 3:

pod "RxSwiftExt", '2.5.1'

If you use Swift 2.x:

pod "RxSwiftExt", '1.2'

Carthage

Add this to your Cartfile

github "RxSwiftCommunity/RxSwiftExt"

Operators

RxSwiftExt is all about adding operators and Reactive Extensions to RxSwift!

Operators

These operators are much like the RxSwift & RxCocoa core operators, but provide additional useful abilities to your Rx arsenal.

There are two more available operators for materialize()'d sequences:

Read below for details about each operator.

Reactive Extensions

RxSwift/RxCocoa Reactive Extensions are provided to enhance existing objects and classes from the Apple-ecosystem with Reactive abilities.


Operator details

unwrap

Unwrap optionals and filter out nil values.

  Observable.of(1,2,nil,Int?(4))
    .unwrap()
    .subscribe { print($0) }
next(1)
next(2)
next(4)

ignore

Ignore specific elements.

  Observable.from(["One","Two","Three"])
    .ignore("Two")
    .subscribe { print($0) }
next(One)
next(Three)
completed  

ignoreWhen

Ignore elements according to closure.

  Observable<Int>
    .of(1,2,3,4,5,6)
    .ignoreWhen { $0 > 2 && $0 < 6 }
    .subscribe { print($0) }
next(1)
next(2)
next(6)
completed

once

Send a next element exactly once to the first subscriber that takes it. Further subscribers get an empty sequence.

  let obs = Observable.once("Hello world")
  print("First")
  obs.subscribe { print($0) }
  print("Second")
  obs.subscribe { print($0) }
First
next(Hello world)
completed
Second
completed

distinct

Pass elements through only if they were never seen before in the sequence.

Observable.of("a","b","a","c","b","a","d")
    .distinct()
    .subscribe { print($0) }
next(a)
next(b)
next(c)
next(d)
completed

map

Replace every element with the provided value.

Observable.of(1,2,3)
    .map(to: "Nope.")
    .subscribe { print($0) }
next(Nope.)
next(Nope.)
next(Nope.)
completed

mapAt

Transform every element to the value at the provided key path.

struct Person {
    let name: String
}

Observable
    .of(
        Person(name: "Bart"),
        Person(name: "Lisa"),
        Person(name: "Maggie")
    )
    .mapAt(\.name)
    .subscribe { print($0) }
next(Bart)
next(Lisa)
next(Maggie)
completed

not

Negate booleans.

Observable.just(false)
    .not()
    .subscribe { print($0) }
next(true)
completed

and

Verifies that every value emitted is true

Observable.of(true, true)
	.and()
	.subscribe { print($0) }

Observable.of(true, false)
	.and()
	.subscribe { print($0) }

Observable<Bool>.empty()
	.and()
	.subscribe { print($0) }

Returns a Maybe<Bool>:

success(true)
success(false)
completed

cascade

Sequentially cascade through a list of observables, dropping previous subscriptions as soon as an observable further down the list starts emitting elements.

let a = PublishSubject<String>()
let b = PublishSubject<String>()
let c = PublishSubject<String>()
Observable.cascade([a,b,c])
    .subscribe { print($0) }
a.onNext("a:1")
a.onNext("a:2")
b.onNext("b:1")
a.onNext("a:3")
c.onNext("c:1")
a.onNext("a:4")
b.onNext("b:4")
c.onNext("c:2")
next(a:1)
next(a:2)
next(b:1)
next(c:1)
next(c:2)

pairwise, nwise

Groups elements emitted by an Observable into arrays, where each array consists of the last N consecutive items; similar to a sliding window.

Observable.from([1, 2, 3, 4, 5, 6])
    .pairwise()
    .subscribe { print($0) }
next((1, 2))
next((2, 3))
next((3, 4))
next((4, 5))
next((5, 6))
completed

retry

Repeats the source observable sequence using given behavior in case of an error or until it successfully terminated. There are four behaviors with various predicate and delay options: immediate, delayed, exponentialDelayed and customTimerDelayed.

// in case of an error initial delay will be 1 second,
// every next delay will be doubled
// delay formula is: initial * pow(1 + multiplier, Double(currentAttempt - 1)), so multiplier 1.0 means, delay will doubled
_ = sampleObservable.retry(.exponentialDelayed(maxCount: 3, initial: 1.0, multiplier: 1.0), scheduler: delayScheduler)
    .subscribe(onNext: { event in
        print("Receive event: \(event)")
    }, onError: { error in
        print("Receive error: \(error)")
    })
Receive event: First
Receive event: Second
Receive event: First
Receive event: Second
Receive event: First
Receive event: Second
Receive error: fatalError

repeatWithBehavior

Repeats the source observable sequence using given behavior when it completes. This operator takes the same parameters as the retry operator. There are four behaviors with various predicate and delay options: immediate, delayed, exponentialDelayed and customTimerDelayed.

// when the sequence completes initial delay will be 1 second,
// every next delay will be doubled
// delay formula is: initial * pow(1 + multiplier, Double(currentAttempt - 1)), so multiplier 1.0 means, delay will doubled
_ = completingObservable.repeatWithBehavior(.exponentialDelayed(maxCount: 3, initial: 1.0, multiplier: 1.2), scheduler: delayScheduler)
    .subscribe(onNext: { event in
        print("Receive event: \(event)")
})
Receive event: First
Receive event: Second
Receive event: First
Receive event: Second
Receive event: First
Receive event: Second

catchErrorJustComplete

Completes a sequence when an error occurs, dismissing the error condition

let _ = sampleObservable
    .do(onError: { print("Source observable emitted error \($0), ignoring it") })
    .catchErrorJustComplete()
    .subscribe {
        print ("\($0)")
}
next(First)
next(Second)
Source observable emitted error fatalError, ignoring it
completed

pausable

Pauses the elements of the source observable sequence unless the latest element from the second observable sequence is true.

let observable = Observable<Int>.interval(1, scheduler: MainScheduler.instance)

let trueAtThreeSeconds = Observable<Int>.timer(3, scheduler: MainScheduler.instance).map { _ in true }
let falseAtFiveSeconds = Observable<Int>.timer(5, scheduler: MainScheduler.instance).map { _ in false }
let pauser = Observable.of(trueAtThreeSeconds, falseAtFiveSeconds).merge()

let pausedObservable = observable.pausable(pauser)

let _ = pausedObservable
    .subscribe { print($0) }
next(2)
next(3)

More examples are available in the project's Playground.

pausableBuffered

Pauses the elements of the source observable sequence unless the latest element from the second observable sequence is true. Elements emitted by the source observable are buffered (with a configurable limit) and "flushed" (re-emitted) when the observable resumes.

Examples are available in the project's Playground.

apply

Apply provides a unified mechanism for applying transformations on Observable sequences, without having to extend ObservableType or repeating your transformations. For additional rationale for this see discussion on github

// An ordinary function that applies some operators to its argument, and returns the resulting Observable
func requestPolicy(_ request: Observable<Void>) -> Observable<Response> {
    return request.retry(maxAttempts)
        .do(onNext: sideEffect)
        .map { Response.success }
        .catchError { error in Observable.just(parseRequestError(error: error)) }

// We can apply the function in the apply operator, which preserves the chaining style of invoking Rx operators
let resilientRequest = request.apply(requestPolicy)

filterMap

A common pattern in Rx is to filter out some values, then map the remaining ones to something else. filterMap allows you to do this in one step:

// keep only odd numbers and double them
Observable.of(1,2,3,4,5,6)
	.filterMap { number in
		(number % 2 == 0) ? .ignore : .map(number * 2)
	}

The sequence above keeps even numbers 2, 4, 6 and produces the sequence 4, 8, 12.

errors, elements

These operators only apply to observable serquences that have been materialized with the materialize() operator (from RxSwift core). errors returns a sequence of filtered error events, ommitting elements. elements returns a sequence of filtered element events, ommitting errors.

let imageResult = _chooseImageButtonPressed.asObservable()
    .flatMap { imageReceiver.image.materialize() }
    .share()

let image = imageResult
    .elements()
    .asDriver(onErrorDriveWith: .never())

let errorMessage = imageResult
    .errors()
    .map(mapErrorMessages)
    .unwrap()
    .asDriver(onErrorDriveWith: .never())

fromAsync

Turns simple asynchronous completion handlers into observable sequences. Suitable for use with existing asynchronous services which call a completion handler with only one parameter. Emits the result produced by the completion handler then completes.

func someAsynchronousService(arg1: String, arg2: Int, completionHandler:(String) -> Void) {
    // a service that asynchronously calls
	// the given completionHandler
}

let observableService = Observable
    .fromAsync(someAsynchronousService)

observableService("Foo", 0)
    .subscribe(onNext: { (result) in
        print(result)
    })
    .disposed(by: disposeBag)

zipWith

Convenience version of Observable.zip(_:). Merges the specified observable sequences into one observable sequence by using the selector function whenever all of the observable sequences have produced an element at a corresponding index.

let first = Observable.from(numbers)
let second = Observable.from(strings)

first.zip(with: second) { i, s in
        s + String(i)
    }.subscribe(onNext: { (result) in
        print(result)
    })
next("a1")
next("b2")
next("c3")

ofType

The ofType operator filters the elements of an observable sequence, if that is an instance of the supplied type.

Observable.of(NSNumber(value: 1),
                  NSDecimalNumber(string: "2"),
                  NSNumber(value: 3),
                  NSNumber(value: 4),
                  NSDecimalNumber(string: "5"),
                  NSNumber(value: 6))
        .ofType(NSDecimalNumber.self)
        .subscribe { print($0) }
next(2)
next(5)
completed

This example emits 2, 5 (NSDecimalNumber Type).

withUnretained

The withUnretained(_:resultSelector:) operator provides an unretained, safe to use (i.e. not implicitly unwrapped), reference to an object along with the events emitted by the sequence. In the case the provided object cannot be retained successfully, the seqeunce will complete.

class TestClass: CustomStringConvertible {
    var description: String { return "Test Class" }
}

Observable
    .of(1, 2, 3, 5, 8, 13, 18, 21, 23)
    .withUnretained(testClass)
    .do(onNext: { _, value in
        if value == 13 {
            // When testClass becomes nil, the next emission of the original
            // sequence will try to retain it and fail. As soon as it fails,
            // the sequence will complete.
            testClass = nil
        }
    })
    .subscribe()
next((Test Class, 1))
next((Test Class, 2))
next((Test Class, 3))
next((Test Class, 5))
next((Test Class, 8))
next((Test Class, 13))
completed

Reactive Extensions details

UIViewPropertyAnimator.animate

The animate(afterDelay:) operator provides a Completable that triggers the animation upon subscription and completes when the animation ends.

button.rx.tap
    .flatMap {
        animator1.rx.animate()
            .andThen(animator2.rx.animate(afterDelay: 0.15))
            .andThen(animator3.rx.animate(afterDelay: 0.1))
    }

UIViewPropertyAnimator.fractionComplete

The fractionComplete binder provides a reactive way to bind to UIViewPropertyAnimator.fractionComplete.

slider.rx.value.map(CGFloat.init)
    .bind(to: animator.rx.fractionComplete)

License

This library belongs to RxSwiftCommunity.

RxSwiftExt is available under the MIT license. See the LICENSE file for more info.