# catchError

## 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**

![](/files/-MWlwOv5oWwPdVi59JVP)

**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

```swift
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)

recoverySequence.onNext("😊")
```

**输出结果：**

```swift
next(😬)
next(😨)
next(😡)
next(🔴)
Error: test
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

```swift
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)
```

**输出结果：**

```swift
next(😬)
next(😨)
next(😡)
next(🔴)
next(😊)
completed
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://3440217568.gitbook.io/rxswift/decision_tree/catcherror.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.