注意：使用本例中的代碼首先應(yīng)該導(dǎo)入頭文件，代碼如下：

import RxSwift

Filtering and Conditional Operators

有選擇地從源Observable序列發(fā)散元素的操作。

filter

發(fā)散一個源Observable序列中滿足指定條件的那些元素。?了解更多

example("filter") {
    let disposeBag = DisposeBag()

    Observable.of(
        "??", "??", "??",
        "??", "??", "??",
        "??", "??", "??")
        .filter {
            $0 == "??"
        }
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}

Debug Area 輸出：
--- filter example ---
??
??
??

distinctUntilChanged

壓縮一個源Observable序列中發(fā)散的連續(xù)重復(fù)的元素。?了解更多

example("distinctUntilChanged") {
    let disposeBag = DisposeBag()

    Observable.of("??", "??", "??", "??", "??", "??", "??")
        .distinctUntilChanged()
        .subscribe(onNext:  { print($0) })
        .disposed(by: disposeBag)
}

Debug Area 輸出：
--- distinctUntilChanged example ---
??
??
??
??
??

elementAt

發(fā)散一個源Observable序列中指定索引的元素。?了解更多

example("elementAt") {
    let disposeBag = DisposeBag()

    Observable.of("??", "??", "??", "??", "??", "??")
        .elementAt(3)
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}

Debug Area 輸出：
--- elementAt example ---
??

single

發(fā)出一個源Observable序列中的第一個元素(或者滿足條件的第一個元素)。如果這個源Observable序列不能發(fā)出一個元素或者根據(jù)條件查找到兩個以上的元素將會?拋出一個錯誤。

example("single") {
    let disposeBag = DisposeBag()

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

Debug Area 輸出：
--- single example ---
??

example("single with conditions") {
    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)
}

Debug Area 輸出：
--- single with conditions example ---
next(??)
completed
next(??)
error(Sequence contains more than one element.)
error(Sequence doesn't contain any elements.)

take

從一個源Observable序列的開始元素?發(fā)散指定數(shù)量的元素。?了解更多

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

Debug Area 輸出：
--- take example ---
??
??
??

takeLast

從一個源Observable序列的結(jié)尾元素?發(fā)散指定數(shù)量的元素。?了解更多

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

Debug Area 輸出：
--- takeLast example ---
??
??
??

takeWhile

發(fā)出一個源Observable序列中?的只要指定條件的值為true的元素。?了解更多

image

example("takeWhile") {
    let disposeBag = DisposeBag()

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

Debug Area 輸出：
--- takeWhile example ---
1
2
3

takeUntil

從一個源Observable序列中?發(fā)散元素直到一個參照Observable序列發(fā)出一個元素。?了解更多

example("takeUntil") {
    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("??")
}

Debug Area 輸出：
--- takeUntil example ---
next(??)
next(??)
next(??)
completed

skip

從一個源Observable序列的開始發(fā)散元素，并且跳過指定數(shù)量的元素。了解更多

example("skipWhile") {
    let disposeBag = DisposeBag()

    Observable.of("??", "??", "??", "??", "??", "??")
        .skip(2)
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}

Debug Area 輸出：
--- skip example ---
??
??
??
??

skipWhile

從一個源Observable序列的開始發(fā)散元素，并且跳過滿足條件的元素。了解更多

example("skipWhile") {
    let disposeBag = DisposeBag()

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

Debug Area 輸出：
--- skipWhile example ---
4
5
6

skipWhileWithIndex

從一個源Observable序列的開始發(fā)散元素，并且跳過滿足條件的索引的元素。這個閉包查詢了每個元素。

example("skipWhileWith") {
    let disposeBag = DisposeBag()

    Observable.of("??", "??", "??", "??", "??", "??")
        .skipWhileWithIndex { element, index in
            index < 3
        }
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}

Debug Area 輸出：
--- skipWhileWithIndex example ---
??
??
??

skipUntil

跳過一個源Observable序列發(fā)送的元素，直到一個參照Observable序列發(fā)出一個元素。了解更多

example("skipUntil") {
    let disposeBag = DisposeBag()

    let sourceSequence = PublishSubject<String>()
    let referenceSequence = PublishSubject<String>()

    sourceSequence
        .skipUntil(referenceSequence)
        .subscribe { print($0) }
        .disposed(by: disposeBag)

    sourceSequence.onNext("??")
    sourceSequence.onNext("??")
    sourceSequence.onNext("??")

    referenceSequence.onNext("??")

    sourceSequence.onNext("??")
    sourceSequence.onNext("??")
    sourceSequence.onNext("??")
}

Debug Area 輸出：
--- skipUntil example ---
??
??
??

下一篇： 八、??數(shù)學(xué)和?集合操作-Mathematical and Aggregate Operators(Rx.playground翻譯)?