Question

据我所知，RxJava2 values.take(1)创建了另一个Observable，它只包含原始Observable中的一个元素。哪个绝不能抛出异常，因为它被take(1)的影响过滤掉了，因为它发生了第二次。

与以下代码段

中一样

    Observable<Integer> values = Observable.create(o -> {
        o.onNext(1);
        o.onError(new Exception("Oops"));
    });

    values.take(1)
            .subscribe(
                    System.out::println,
                    e -> System.out.println("Error: " + e.getMessage()),
                    () -> System.out.println("Completed")
            );

输出

1
Completed
io.reactivex.exceptions.UndeliverableException: java.lang.Exception: Oops
    at io.reactivex.plugins.RxJavaPlugins.onError(RxJavaPlugins.java:366)
    at io.reactivex.internal.operators.observable.ObservableCreate$CreateEmitter.onError(ObservableCreate.java:83)
    at ch02.lambda$main$0(ch02.java:28)
    at io.reactivex.internal.operators.observable.ObservableCreate.subscribeActual(ObservableCreate.java:40)
    at io.reactivex.Observable.subscribe(Observable.java:10841)
    at io.reactivex.internal.operators.observable.ObservableTake.subscribeActual(ObservableTake.java:30)
    at io.reactivex.Observable.subscribe(Observable.java:10841)
    at io.reactivex.Observable.subscribe(Observable.java:10827)
    at io.reactivex.Observable.subscribe(Observable.java:10787)
    at ch02.main(ch02.java:32)
Caused by: java.lang.Exception: Oops
    ... 8 more
Exception in thread "main" io.reactivex.exceptions.UndeliverableException: java.lang.Exception: Oops
    at io.reactivex.plugins.RxJavaPlugins.onError(RxJavaPlugins.java:366)
    at io.reactivex.internal.operators.observable.ObservableCreate$CreateEmitter.onError(ObservableCreate.java:83)
    at ch02.lambda$main$0(ch02.java:28)
    at io.reactivex.internal.operators.observable.ObservableCreate.subscribeActual(ObservableCreate.java:40)
    at io.reactivex.Observable.subscribe(Observable.java:10841)
    at io.reactivex.internal.operators.observable.ObservableTake.subscribeActual(ObservableTake.java:30)
    at io.reactivex.Observable.subscribe(Observable.java:10841)
    at io.reactivex.Observable.subscribe(Observable.java:10827)
    at io.reactivex.Observable.subscribe(Observable.java:10787)
    at ch02.main(ch02.java:32)
Caused by: java.lang.Exception: Oops
    ... 8 more

我的问题：

我理解它是否正确？
造成例外的真正原因。
如何从消费者那里解决这个问题？

Answer 1

是的，但因为可观察的“结束”并不意味着create(...)内运行的代码已停止。要在这种情况下完全安全，您需要使用o.isDisposed()来查看observable是否已经在下游结束。
由于RxJava 2的策略是永远不允许onError调用丢失，因此存在异常。如果observable已经终止，它将作为全局UndeliverableException传递到下游或抛出。由Observable的创建者“正确”处理observable已经结束并发生异常的情况。
问题是生产者（Observable）和消费者（Subscriber）在流结束时不一致。由于生产者在这种情况下比消费者寿命长，因此问题只能在生产者中解决。

Answer 2

@Kiskae在之前的评论中正确回答了可能发生此类异常的原因。

此处指向此主题的官方文档的链接：RxJava2-wiki。

有时您无法更改此行为，因此有一种方法可以处理此UndeliverableException。以下是如何避免崩溃和错误行为的代码片段：

RxJavaPlugins.setErrorHandler(e -> {
    if (e instanceof UndeliverableException) {
        e = e.getCause();
    }
    if ((e instanceof IOException) || (e instanceof SocketException)) {
        // fine, irrelevant network problem or API that throws on cancellation
        return;
    }
    if (e instanceof InterruptedException) {
        // fine, some blocking code was interrupted by a dispose call
        return;
    }
    if ((e instanceof NullPointerException) || (e instanceof IllegalArgumentException)) {
        // that's likely a bug in the application
        Thread.currentThread().getUncaughtExceptionHandler()
            .handleException(Thread.currentThread(), e);
        return;
    }
    if (e instanceof IllegalStateException) {
        // that's a bug in RxJava or in a custom operator
        Thread.currentThread().getUncaughtExceptionHandler()
            .handleException(Thread.currentThread(), e);
        return;
    }
    Log.warning("Undeliverable exception received, not sure what to do", e);
});

此代码取自上面的链接。

重要提示。这种方法将全局错误处理程序设置为RxJava，因此如果您能够摆脱这些异常 - 那将是更好的选择。

Answer 3

使用observable.create（）时，只需要使用tryOnError（）。 onError（）不能保证错误会得到处理。有error handling operators种HERE

Answer 4

科特林

我通过MainActivity onCreate方法对此进行了校准

private fun initRxErrorHandler(){
    RxJavaPlugins.setErrorHandler { throwable ->
        if (throwable is UndeliverableException) {
            throwable.cause?.let {
                Thread.currentThread().uncaughtExceptionHandler?.uncaughtException(Thread.currentThread(), it)
                return@setErrorHandler
            }
        }
        if (throwable is IOException || throwable is SocketException) {
            // fine, irrelevant network problem or API that throws on cancellation
            return@setErrorHandler
        }
        if (throwable is InterruptedException) {
            // fine, some blocking code was interrupted by a dispose call
            return@setErrorHandler
        }
        if (throwable is NullPointerException || throwable is IllegalArgumentException) {
            // that's likely a bug in the application
            Thread.currentThread().uncaughtExceptionHandler?.uncaughtException(Thread.currentThread(), throwable)
            return@setErrorHandler
        }
        if (throwable is IllegalStateException) {
            // that's a bug in RxJava or in a custom operator
            Thread.currentThread().uncaughtExceptionHandler?.uncaughtException(Thread.currentThread(), throwable)
            return@setErrorHandler
        }
        Log.w("Undeliverable exception", throwable)
    }
}

RxJava2 observable抛出UndeliverableException

输出

我的问题：

4 个答案: