从源可观察序列中选择性地发射元素的操作。
filter
仅从符合指定条件的可观察序列中发出这些元素。
let disposeBag = DisposeBag()
Observable.of(
"🐱", "🐰", "🐶",
"🐸", "🐱", "🐰",
"🐹", "🐸", "🐱")
.filter {
$0 == "🐱"
}
.subscribe(onNext: { print($0) })
.disposed(by: disposeBag)
distinctUntilChanged
抑制可观察序列发出的序列重复元素。
let disposeBag = DisposeBag()
Observable.of("🐱", "🐷", "🐱", "🐱", "🐱", "🐵", "🐱")
.distinctUntilChanged()
.subscribe(onNext: { print($0) })
.disposed(by: disposeBag) //🐱🐷🐱🐵🐱
elementAt
仅在可观察序列中发出的所有元素的指定索引中释放元素。
let disposeBag = DisposeBag()
Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
.elementAt(3)
.subscribe(onNext: { print($0) })
.disposed(by: disposeBag) // 🐸
single
只发出可观察序列发出的第一个元素（或满足条件的第一个元素）。如果可观察序列不是恰好发射一个元素，（多个满足条件的）则抛出一个错误。
let disposeBag = DisposeBag()
Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
.single()
.subscribe(onNext: { print($0) })
.disposed(by: disposeBag)
加条件
let disposeBag = DisposeBag()
Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
.single { $0 == "🐸" }
.subscribe { print($0) }
.disposed(by: disposeBag) // next(🐸) completed
Observable.of("🐱", "🐰", "🐶", "🐱", "🐰", "🐶")
.single { $0 == "🐰" }
.subscribe { print($0) }
.disposed(by: disposeBag) // next(🐰) error(Sequence contains more than one element.)
Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
.single { $0 == "🔵" }
.subscribe { print($0) }
.disposed(by: disposeBag) // error(Sequence doesn't contain any elements.)
take
仅从可观察序列的开头发出指定数量的元素
let disposeBag = DisposeBag()
Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
.take(3)
.subscribe(onNext: { print($0) })
.disposed(by: disposeBag) // 🐱🐰🐶
takeLast
仅从可观察序列的结尾发出指定数量的元素。
let disposeBag = DisposeBag()
Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
.takeLast(3)
.subscribe(onNext: { print($0) })
.disposed(by: disposeBag) // 🐸🐷🐵
takeWhile
只要指定的条件求值为true，则从可观察序列的开头发出元素。
let disposeBag = DisposeBag()
Observable.of(1, 2, 3, 4, 5, 6)
.takeWhile { $0 < 4 }
.subscribe(onNext: { print($0) })
.disposed(by: disposeBag) // 1 2 3
takeUntil
从源可观察序列中释放元素，直到引用可观察序列发出元素结束（发照发，有人来了就不发了）
let disposeBag = DisposeBag()
let sourceSequence = PublishSubject<String>()
let referenceSequence = PublishSubject<String>()
sourceSequence
.takeUntil(referenceSequence)
.subscribe { print($0) }
.disposed(by: disposeBag)
sourceSequence.onNext("🐱")
sourceSequence.onNext("🐰")
sourceSequence.onNext("🐶")
referenceSequence.onNext("🔴")
sourceSequence.onNext("🐸")
sourceSequence.onNext("🐷")
sourceSequence.onNext("🐵") // next(🐱) next(🐰) next(🐶) completed
skip
禁止从可观察序列的开头释放指定数量的元素。
let disposeBag = DisposeBag()
Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
.skip(2)
.subscribe(onNext: { print($0) })
.disposed(by: disposeBag) // 🐶🐸🐷🐵
shipWhile
禁止从符合指定条件的可观察序列的开头发出元素。
let disposeBag = DisposeBag()
Observable.of(1, 2, 3, 4, 5, 6)
.skipWhile { $0 < 4 }
.subscribe(onNext: { print($0) })
.disposed(by: disposeBag) // 4 5 6
skipWhileWithIndex
禁止从符合指定条件的可观察序列的开头发出元素，并发出剩余的元素。闭包可用通过每个元素的索引。
let disposeBag = DisposeBag()
Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
.skipWhileWithIndex { element, index in
index < 3
}
.subscribe(onNext: { print($0) })
.disposed(by: disposeBag) // 🐸🐷🐵
skipUntil
禁止从源可观察序列中释放元素，直到引用可观察序列发出元素。
let disposeBag = DisposeBag()
let sourceSequence = PublishSubject<String>()
let referenceSequence = PublishSubject<String>()
sourceSequence
.skipUntil(referenceSequence)
.subscribe(onNext: { print($0) })
.disposed(by: disposeBag)
sourceSequence.onNext("🐱")
sourceSequence.onNext("🐰")
sourceSequence.onNext("🐶")
referenceSequence.onNext("🔴")
sourceSequence.onNext("🐸")
sourceSequence.onNext("🐷")
sourceSequence.onNext("🐵") // 🐸🐷🐵
