ichina / rxswiftext

Additional operators not found in the core RxSwift distribution

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.

Installation

RxSwiftExt requires Swift 3 and RxSwift 3.0 or later. If your project is running on Swift 2.x, please use version 1.2 of the library.

CocoaPods

Using Swift 3:

pod "RxSwiftExt"

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 to RxSwift! Currently available operators:

• unwrap
• ignore
• ignoreWhen
• Observable.once
• distinct
• mapTo
• not
• Observable.cascade
• retry
• repeatWithBehavior
• catchErrorJustComplete
• pausable
• apply

Two additional operators are available for `materialize()'d sequences:

• errors
• elements

Read below for details about each operator.

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

mapTo

Replace every element with the provided value.

Observable.of(1,2,3)
    .mapTo("Nope.")
    .subscribe { print($0) }

Next(Nope.)
Next(Nope.)
Next(Nope.)
Completed

not

Negate booleans.

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

Next(true)
Completed

cascade

Sequentially cascade through a list of observable, 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)

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.

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)

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())

License

This library belongs to RxSwiftCommunity.

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