（*useful）标记：目前觉得有用的函数 //FIXME 标记：待补充 ##帮助捕获错误，并可以发送消息，平滑的处理error

####catchErrorJustReturn

example("catchErrorJustReturn") {let disposeBag = DisposeBag()let sequenceThatFails = PublishSubject<String>()sequenceThatFails.catchErrorJustReturn("?").subscribe { print($0) }.disposed(by: disposeBag)sequenceThatFails.onNext("?")sequenceThatFails.onNext("?")sequenceThatFails.onNext("?")sequenceThatFails.onNext("?")sequenceThatFails.onError(TestError.test)
}
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打印： --- catchErrorJustReturn example --- next(?) next(?) next(?) next(?) next(?) //捕获的error completed

####catchError: 捕获错误，并return一个Observable sequence

example("catchError") {let disposeBag = DisposeBag()let sequenceThatFails = PublishSubject<String>()let recoverySequence = PublishSubject<String>()sequenceThatFails.catchError {print("Error:", $0)return recoverySequence}.subscribe { print($0) }.disposed(by: disposeBag)sequenceThatFails.onNext("?")sequenceThatFails.onNext("?")sequenceThatFails.onNext("?")sequenceThatFails.onNext("?")sequenceThatFails.onError(TestError.test)sequenceThatFails.onNext("errored")  recoverySequence.onNext("?")
}
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打印： next(?) next(?) next(?) next(?) Error: test //切换到了recoverySequence next(?)

####retry
#####重复订阅onError的sequence，indefinitely（可无限订阅

example("retry") {let disposeBag = DisposeBag()var count = 1let sequenceThatErrors = Observable<String>.create { observer inobserver.onNext("?")observer.onNext("?")observer.onNext("?")if count == 1 {observer.onError(TestError.test)print("Error encountered")count += 1}observer.onNext("?")observer.onNext("?")observer.onNext("?")observer.onCompleted()return Disposables.create()}sequenceThatErrors.retry().subscribe(onNext: { print($0) }).disposed(by: disposeBag)
}
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打印： --- retry example --- ? ? ? Error encountered ? //retry从这里开始 ，demo只进行了一个次error ? ? ? ? ?

####retry(_:) 跟上面的一样，加入了参数（控制retry的次数）

example("retry maxAttemptCount") {let disposeBag = DisposeBag()var count = 1let sequenceThatErrors = Observable<String>.create { observer inobserver.onNext("?")observer.onNext("?")observer.onNext("?")if count < 5 {observer.onError(TestError.test)print("Error encountered")count += 1}observer.onNext("?")observer.onNext("?")observer.onNext("?")observer.onCompleted()return Disposables.create()}sequenceThatErrors.retry(3).subscribe(onNext: { print($0) }).disposed(by: disposeBag)
}
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打印： --- retry maxAttemptCount example --- ? ? ? Error encountered ? ? ? Error encountered ? ? ? Error encountered Unhandled error happened: test subscription called from: