catchError

从一个错误事件中恢复，将错误事件替换成一个备选序列

catchError 操作符将会拦截一个 error 事件，将它替换成其他的元素或者一组元素，然后传递给观察者。这样可以使得 Observable 正常结束，或者根本都不需要结束。

这里存在其他版本的 catchError 操作符。

演示

1. let disposeBag = DisposeBag()

3. let sequenceThatFails = PublishSubject<String>()
4. let recoverySequence = PublishSubject<String>()

6. sequenceThatFails
7. .catchError {
8. print("Error:", $0)
9. return recoverySequence
10. }
11. .subscribe { print($0) }
12. .disposed(by: disposeBag)

14. sequenceThatFails.onNext("?")
15. sequenceThatFails.onNext("?")
16. sequenceThatFails.onNext("?")
17. sequenceThatFails.onNext("?")
18. sequenceThatFails.onError(TestError.test)

20. recoverySequence.onNext("?")

输出结果：

1. next(?)
2. next(?)
3. next(?)
4. next(?)
5. Error: test
6. next(?)

catchErrorJustReturn

catchErrorJustReturn 操作符会将error 事件替换成其他的一个元素，然后结束该序列。

演示

1. let disposeBag = DisposeBag()
2. let sequenceThatFails = PublishSubject<String>()

4. sequenceThatFails
5. .catchErrorJustReturn("?")
6. .subscribe { print($0) }
7. .disposed(by: disposeBag)

9. sequenceThatFails.onNext("?")
10. sequenceThatFails.onNext("?")
11. sequenceThatFails.onNext("?")
12. sequenceThatFails.onNext("?")
13. sequenceThatFails.onError(TestError.test)

输出结果：

1. next(?)
2. next(?)
3. next(?)
4. next(?)
5. next(?)
6. completed