android - RxJava返回错误为onNext并继续流

Question

所以我试图使用onErrorReturn返回我想要的结果，但是它将在之后完成流，如何捕获错误返回为Next并仍然继续流？

使用下面的代码，如果出现错误，它将不会到达retryWhen，如果我将其翻转，如果出现错误，它将不会重新订阅retryWhen

fun process(): Observable<State> {
    return publishSubject
        .flatMap { intent ->
            actAsRepo(intent) // Might return error
                .map { State(data = it, error = null) }
        }
        .onErrorReturn { State(data = "", error = it) } // catch the error
        .retryWhen { errorObs -> 
            errorObs.flatMap {
                Observable.just(State.defaultState()) // continue subscribing
            }
        }
}

private fun actAsRepo(string: String): Observable<String> {
    if (string.contains('A')) {
        throw IllegalArgumentException("Contains A")
    } else {
        return Observable.just("Wrapped from repo: $string")
    }
}

订户将是

viewModel.process().subscribe(this::render)

Answer 1

onError是终端运算符(operator)。如果发生onError，它将在运算符之间传递。您可以使用onError-operator来捕获onError并提供备用。

在您的示例中，onError发生在flatMap的内部流中。 onError将向下游传播到onErrorReturn操作者。如果看一下实现，您将看到将调用onErrorReturn lambda，结果将在onComplete之后通过onNext向下游推送

    @Override
    public void onError(Throwable t) {
        T v;
        try {
            v = valueSupplier.apply(t);
        } catch (Throwable e) {
            Exceptions.throwIfFatal(e);
            downstream.onError(new CompositeException(t, e));
            return;
        }

        if (v == null) {
            NullPointerException e = new NullPointerException("The supplied value is null");
            e.initCause(t);
            downstream.onError(e);
            return;
        }

        downstream.onNext(v); // <--------
        downstream.onComplete(); // <--------
    }

您的解决方案是什么结果？

由于以下原因，您的流完成了:#retry当JavaDoc

If the upstream to the operator is asynchronous, signalling onNext followed by onComplete immediately may result in the sequence to be completed immediately. Similarly, if this inner {@code ObservableSource} signals {@code onError} or {@code onComplete} while the upstream is active, the sequence is terminated with the same signal immediately.

您应该做什么:

将onErrorReturn放置在flatMap中的 map 操作者之后。通过这种排序，当inner-flatMap流onErrors时，您的流将无法完成。

为什么是这样？

当外部(源:publishSubject)和内部流(订阅)都完成时，flatMap运算符完成。在这种情况下，外部流(publishSubject)发出onNext，内部流将在通过onNext发送{State(data =“”，error = it)}之后完成。因此，流将保持打开状态。

interface ApiCall {
    fun call(s: String): Observable<String>
}

class ApiCallImpl : ApiCall {
    override fun call(s: String): Observable<String> {
        // important: warp call into observable, that the exception is caught and emitted as onError downstream
        return Observable.fromCallable {
            if (s.contains('A')) {
                throw IllegalArgumentException("Contains A")
            } else {
                s
            }
        }
    }
}

data class State(val data: String, val err: Throwable? = null)

apiCallImpl.call将返回一个可延迟的可观察对象，这将在订阅时引发错误，而不是在可观察的组装时抛出错误。

// no need for retryWhen here, except you want to catch onComplete from the publishSubject, but once the publishSubject completes no re-subscription will help you, because the publish-subject is terminated and onNext invocations will not be accepted anymore (see implementation). 
fun process(): Observable<State> {
    return publishSubject
        .flatMap { intent ->
            apiCallImpl.call(intent) // Might return error
                .map { State(data = it, err = null) }
                .onErrorReturn { State("", err = it) }
        }
}

测试

lateinit var publishSubject: PublishSubject<String>
lateinit var apiCallImpl: ApiCallImpl

@Before
fun init() {
    publishSubject = PublishSubject.create()
    apiCallImpl = ApiCallImpl()
}

@Test
fun myTest() {
    val test = process().test()

    publishSubject.onNext("test")
    publishSubject.onNext("A")
    publishSubject.onNext("test2")

    test.assertNotComplete()
        .assertNoErrors()
        .assertValueCount(3)
        .assertValueAt(0) {
            assertThat(it).isEqualTo(State("test", null))
            true
        }
        .assertValueAt(1) {
            assertThat(it.data).isEmpty()
            assertThat(it.err).isExactlyInstanceOf(IllegalArgumentException::class.java)
            true
        }
        .assertValueAt(2) {
            assertThat(it).isEqualTo(State("test2", null))
            true
        }
}

另类

该替代方案的行为与第一种解决方案略有不同。 flatMap-Operator带有一个 bool(boolean) 值(delayError)，这将导致吞入onError消息，直到源完成为止。当源完成时，将发出错误。

当异常没有用并且在出现时一定不能记录时，可以使用delayError true

处理

fun process(): Observable<State> {
    return publishSubject
        .flatMap({ intent ->
            apiCallImpl.call(intent)
                .map { State(data = it, err = null) }
        }, true)
}

测试

仅发射两个值。该错误不会转换为后备值。

@Test
fun myTest() {
    val test = process().test()

    publishSubject.onNext("test")
    publishSubject.onNext("A")
    publishSubject.onNext("test2")

    test.assertNotComplete()
        .assertNoErrors()
        .assertValueAt(0) {
            assertThat(it).isEqualTo(State("test", null))
            true
        }
        .assertValueAt(1) {
            assertThat(it).isEqualTo(State("test2", null))
            true
        }
        .assertValueCount(2)
}

注意:我认为您想在这种情况下使用switchMap而不是flatMap。