RxSwift Series (v)

Objective

This article will learn RxSwift about the filter and conditional operators, which are included in the RxSwift :

• filter
• distinctUntilChanged
• elementAt
• single
• take
• takeLast
• takeWhile
• takeUntil
• skip
• skipWhile
• skipWhileWithIndex
• skipUntil

Filter

Observableonly events that meet the filter conditions are emitted in the sequence.

let disposeBag = DisposeBag()    Observable.of(1,2,3,4,5).filter({$0 > 2}).subscribe(onNext: {print($0)}).disposed(by: disposeBag)

Printing results:

345

Distinctuntilchanged

Filter the same events that are emitted continuously

let disposeBag = DisposeBag()Observable.of(1,2,3,3,3,2,2,5,4).distinctUntilChanged().subscribe(onNext: {print($0)}).disposed(by: disposeBag)

Printing results:

123254

ElementAt

ObservableIssue only events at the specified location

let disposeBag = DisposeBag()    Observable.of(1,2,3,5,4).elementAt(2).subscribe(onNext: {print($0)}).disposed(by: disposeBag)

Printing results:

3

Single

Usage One: detects Observable whether a sequence emits an element. If you launch multiple, you will get an error.

let disposeBag = DisposeBag()// error:Sequence contains more than one element// Observable.of(1,2,3).single().subscribe(onNext: {print($0)}).disposed(by: disposeBag)Observable.of(1).single().subscribe(onNext: {print($0)}).disposed(by: disposeBag)

Usage Two: detects Observable whether the sequence emitted by the element contains multiple specified elements, if there are multiple or not, will be an error.

let disposeBag = DisposeBag()Observable.of("??", "??", "??", "??", "??", "??")    .single { $0 == "??" }    .subscribe { print($0) }    .disposed(by: disposeBag)    Observable.of("??", "??", "??", "??", "??", "??")    .single { $0 == "??" }    .subscribe { print($0) }    .disposed(by: disposeBag)    Observable.of("??", "??", "??", "??","??")    .single { $0 == "??" }    .subscribe { print($0) }    .disposed(by: disposeBag)

Printing results:

next(??)completederror(Sequence doesn‘t contain any elements.)next(??)error(Sequence contains more than one element.)

Take

Observableonly the first few events are processed from the start point of the sequence.

let disposeBag = DisposeBag()    Observable.of(1,2,3).take(2).subscribe(onNext: {print($0)}).disposed(by: disposeBag)

Printing results:

12

Takelast

In take contrast, from Observable the end of the sequence, only the first few events are processed.

let disposeBag = DisposeBag()    Observable.of(1,2,3).takeLast(2).subscribe(onNext: {print($0)}).disposed(by: disposeBag)

Printing results:

23

TakeWhile

Only events that meet the criteria are processed. It's no different from the feeling. filter

let disposeBag = DisposeBag()Observable.of(1,2,3,4,5).takeWhile{$0 < 3}.subscribe(onNext: {print($0)}).disposed(by: disposeBag)

Printing results:

12

Takeuntil

Until another Observable sequence emits a signal, the original sequence terminates.

let disposeBag = DisposeBag()    let orinSubject = PublishSubject<Int>()let refreSubject = PublishSubject<Int>()    orinSubject.takeUntil(refreSubject).subscribe(onNext: {print($0)}).disposed(by: disposeBag)    orinSubject.onNext(1)orinSubject.onNext(2)refreSubject.onNext(10)orinSubject.onNext(3)

Printing results:

12

Skip

Observableskips a specified number of elements from a sequence.

let disposeBag = DisposeBag()Observable.of(1,2,3,4,5,6).skip(2).subscribe(onNext: {print($0)}).disposed(by: disposeBag)

Printing results:

3456

SkipWhile

Skips an event that satisfies a condition, and whenever an event is encountered that does not meet the condition, the event and subsequent events (whether or not it satisfies the condition) are emitted.

let disposeBag = DisposeBag()    Observable.of(1,2,3,4,5,6).skipWhile{$0 < 3}.subscribe(onNext: {print($0)}).disposed(by: disposeBag)

Printing results:

3456

Skipwhilewithindex

Skips the event that the index satisfies the condition.

let disposeBag = DisposeBag()Observable.of(1,2,3,4,5,6).skipWhileWithIndex({ (element, index) -> Bool in        index < 3    }).subscribe(onNext: {print($0)}).disposed(by: disposeBag)

Printing results:

456

Skipuntil

Skips Observable all events before another sequence emits an event. With the takeUntil opposite.

let disposeBag = DisposeBag()    let oriSubject = PublishSubject<Int>()let refreSubject = PublishSubject<Int>()    oriSubject.skipUntil(refreSubject).subscribe(onNext: {print($0)}).disposed(by: disposeBag)    oriSubject.onNext(1)oriSubject.onNext(2)    refreSubject.onNext(10)oriSubject.onNext(3)oriSubject.onNext(4)

Printing results:

34

Thanks

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RxSwift Series (v)