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 - 图1

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