RxJava doOnError 和 onErrorReturn 是如何工作的？

How does RxJava doOnError and onErrorReturn work?

提问by Nilzor

I made these unit tests, and the outcome is not what I expected at all:

我做了这些单元测试，结果完全不是我所期望的：

// This one outputs "subscribe.onError" 
@Test
public void observable_doOnError_subscribingToError() throws InterruptedException {
    Observable<String> obs = getErrorProducingObservable();
    obs.doOnError(throwable -> System.out.println("doOnError"));
    obs.subscribeOn(Schedulers.immediate()).observeOn(Schedulers.immediate()).subscribe(
        s -> {},
        error -> System.out.println("subscribe.onError")
    );
    Thread.sleep(300);
}

// This one outputs "subscribe.onError" 
@Test
public void observable_onErrorReturn() throws InterruptedException {
    Observable<String> obs = getErrorProducingObservable();
    obs.onErrorReturn(throwable -> "Yeah I got this");
    obs.subscribeOn(Schedulers.immediate()).observeOn(Schedulers.immediate()).subscribe(
        s -> System.out.println("got: " + s),
        error -> System.out.println("subscribe.onError")
    );
    Thread.sleep(300);
}

private Observable<String> getErrorProducingObservable()  {
    return Observable.create(subscriber -> {
        subscriber.onError(new RuntimeException("Somebody set up us the bomb"));
    });
}

So both output "subscribe.onError" - neither doOnErrornor onErrorReturnseems to be called.

所以两个输出“subscribe.onError” -似乎也doOnError没有onErrorReturn被调用。

doOnErroris documented as:

doOnError记录为：

Modifies the source Observable so that it invokes an action if it calls onError.

修改源 Observable 使其在调用 onError 时调用操作。

I'm not sure how to intepret that, but I expected either "doOnError" to be output or "doOnError" followed by "subscribe.onError".

我不确定如何解释这一点，但我希望输出“doOnError”或“doOnError”后跟“subscribe.onError”。

onErrorReturnis documented as :

onErrorReturn记录为：

Instructs an Observable to emit an item (returned by a specified function) rather than invoking onError if it encounters an error.

指示 Observable 发出一个项目（由指定的函数返回），而不是在遇到错误时调用 onError。

Hence I was expecting "got: Yeah I got this" as output from the latter test.

因此，我期待“得到：是的，我得到了这个”作为后一个测试的输出。

What gives?

是什么赋予了？

采纳答案by marstran

Both doOnErrorand onErrorReturnreturns a new Observablewith the changed behaviour. I agree that the documentation of them may be a little misleading. Modify your tests like this to get the expected behaviour:

双方doOnError并onErrorReturn返回一个新的Observable与行为改变。我同意他们的文档可能有点误导。像这样修改您的测试以获得预期的行为：

// This one outputs "subscribe.onError" 
@Test
public void observable_doOnError_subscribingToError() throws InterruptedException {
    Observable<String> obs = 
        getErrorProducingObservable()
            .doOnError(throwable -> System.out.println("doOnError"));

    obs.subscribeOn(Schedulers.immediate()).observeOn(Schedulers.immediate()).subscribe(
        s -> {},
        error -> System.out.println("subscribe.onError")
    );
    Thread.sleep(300);
}

// This one outputs "subscribe.onError" 
@Test
public void observable_onErrorReturn() throws InterruptedException {
    Observable<String> obs = 
        getErrorProducingObservable()
            .onErrorReturn(throwable -> "Yeah I got this");

    obs.subscribeOn(Schedulers.immediate()).observeOn(Schedulers.immediate()).subscribe(
        s -> System.out.println("got: " + s),
        error -> System.out.println("subscribe.onError")
    );
    Thread.sleep(300);
}

private Observable<String> getErrorProducingObservable()  {
    return Observable.create(subscriber -> {
        subscriber.onError(new RuntimeException("Somebody set up us the bomb"));
    });
}