注意：使用本例中的代码首先应该导入头文件，代码如下：

import RxSwift

---

Filtering and Conditional Operators

有选择地从源Observable序列发散元素的操作。

filter

发散一个源Observable序列中满足指定条件的那些元素。�了解更多

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

    Observable.of(
        "🐱", "🐰", "🐶",
        "🐸", "🐱", "🐰",
        "🐹", "🐸", "🐱")
        .filter {
            $0 == "🐱"
        }
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}

Debug Area 输出：
--- filter example ---
🐱
🐱
🐱

---

distinctUntilChanged

压缩一个源Observable序列中发散的连续重复的元素。�了解更多

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

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

Debug Area 输出：
--- distinctUntilChanged example ---
🐱
🐷
🐱
🐵
🐱

---

elementAt

发散一个源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 输出：
--- elementAt example ---
🐸

---

single

发出一个源Observable序列中的第一个元素(或者满足条件的第一个元素)。如果这个源Observable序列不能发出一个元素或者根据条件查找到两个以上的元素将会�抛出一个错误。

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

    Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
        .single()
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}

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

---

take

从一个源Observable序列的开始元素�发散指定数量的元素。�了解更多

example("take") {
    let disposeBag = DisposeBag()
    
    Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
        .take(3)
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}

Debug Area 输出：
--- take example ---
🐱
🐰
🐶

---

takeLast

从一个源Observable序列的结尾元素�发散指定数量的元素。�了解更多

example("takeLast") {
    let disposeBag = DisposeBag()
    
    Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
        .takeLast(3)
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}

Debug Area 输出：
--- takeLast example ---
🐸
🐷
🐵

---

takeWhile

发出一个源Observable序列中�的只要指定条件的值为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 输出：
--- takeWhile example ---
1
2
3

---

takeUntil

从一个源Observable序列中�发散元素直到一个参照Observable序列发出一个元素。�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 输出：
--- takeUntil example ---
next(🐱)
next(🐰)
next(🐶)
completed

---

skip

从一个源Observable序列的开始发散元素，并且跳过指定数量的元素。了解更多

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

    Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
        .skip(2)
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}

Debug Area 输出：
--- skip example ---
🐶
🐸
🐷
🐵

---

skipWhile

从一个源Observable序列的开始发散元素，并且跳过满足条件的元素。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 输出：
--- skipWhile example ---
4
5
6

---

skipWhileWithIndex

从一个源Observable序列的开始发散元素，并且跳过满足条件的索引的元素。这个闭包查询了每个元素。

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

    Observable.of("🐱", "🐰", "🐶", "🐸", "🐷", "🐵")
        .skipWhileWithIndex { element, index in
            index < 3
        }
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)
}

Debug Area 输出：
--- skipWhileWithIndex example ---
🐸
🐷
🐵

---

skipUntil

跳过一个源Observable序列发送的元素，直到一个参照Observable序列发出一个元素。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 输出：
--- skipUntil example ---
🐸
🐷
🐵

---

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