Observable.empty() 导致 java.util.NoSuchElementException：序列不包含元素
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/33005866/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Observable.empty() causes java.util.NoSuchElementException: Sequence contains no elements
提问by Anton Shkurenko
I'm using Retrofit 2.0.0-beta2 with RxJava 1.0.14. I handle errors this way because I need to execute some code in doFinally:
我正在使用带有 RxJava 1.0.14 的 Retrofit 2.0.0-beta2。我这样处理错误是因为我需要在 doFinally 中执行一些代码：
.onErrorResumeNext(Observable.empty());
.onErrorResumeNext(Observable.empty());
But when I get a http response with an error (401 for example) my app crashes with no my classes in the stack trace. Nothing bad happens if use Observable.never. Here's full stack trace:
但是，当我收到带有错误（例如 401）的 http 响应时，我的应用程序崩溃了，堆栈跟踪中没有我的类。如果使用，没有什么不好的事情发生Observable.never。这是完整的堆栈跟踪：
java.lang.IllegalStateException: Exception thrown on Scheduler.Worker thread. Add `onError` handling.
at rx.internal.schedulers.ScheduledAction.run (ScheduledAction.java:60)
at android.os.Handler.handleCallback (Handler.java:739)
at android.os.Handler.dispatchMessage (Handler.java:95)
at android.os.Looper.loop (Looper.java:135)
at android.app.ActivityThread.main (ActivityThread.java:5221)
at java.lang.reflect.Method.invoke (Unknown source)
at java.lang.reflect.Method.invoke (Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:694)
rx.exceptions.OnErrorNotImplementedException: Sequence contains no elements
at rx.Observable.onError (Observable.java:7535)
at rx.observers.SafeSubscriber._onError (SafeSubscriber.java:154)
at rx.observers.SafeSubscriber.onError (SafeSubscriber.java:111)
at rx.internal.operators.OperatorDoOnEach.onError (OperatorDoOnEach.java:70)
at rx.internal.operators.OperatorDoOnEach.onError (OperatorDoOnEach.java:70)
at rx.internal.operators.OperatorDoOnEach.onError (OperatorDoOnEach.java:70)
at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.pollQueue (OperatorObserveOn.java:197)
at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.call (OperatorObserveOn.java:170)
at rx.internal.schedulers.ScheduledAction.run (ScheduledAction.java:55)
at android.os.Handler.handleCallback (Handler.java:739)
at android.os.Handler.dispatchMessage (Handler.java:95)
at android.os.Looper.loop (Looper.java:135)
at android.app.ActivityThread.main (ActivityThread.java:5221)
at java.lang.reflect.Method.invoke (Unknown source)
at java.lang.reflect.Method.invoke (Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:694)
java.util.NoSuchElementException: Sequence contains no elements
at rx.internal.operators.OperatorSingle$ParentSubscriber.onCompleted (OperatorSingle.java:131)
at rx.internal.operators.OperatorTake.onCompleted (OperatorTake.java:53)
at rx.Observable$EmptyHolder.call (Observable.java:1077)
at rx.Observable$EmptyHolder.call (Observable.java:1074)
at rx.Observable.unsafeSubscribe (Observable.java:7710)
at rx.internal.operators.OperatorOnErrorResumeNextViaObservable.onError (OperatorOnErrorResumeNextViaObservable.java:76)
at rx.internal.operators.OperatorDoOnEach.onError (OperatorDoOnEach.java:70)
at rx.internal.operators.OperatorSubscribeOn.onError (OperatorSubscribeOn.java:71)
at rx.observers.SerializedObserver.onError (SerializedObserver.java:159)
at rx.observers.SerializedSubscriber.onError (SerializedSubscriber.java:79)
at rx.internal.operators.OperatorTakeUntil.onError (OperatorTakeUntil.java:49)
at rx.internal.operators.OperatorMerge$MergeSubscriber.reportError (OperatorMerge.java:239)
at rx.internal.operators.OperatorMerge$MergeSubscriber.checkTerminate (OperatorMerge.java:774)
at rx.internal.operators.OperatorMerge$MergeSubscriber.emitLoop (OperatorMerge.java:532)
at rx.internal.operators.OperatorMerge$MergeSubscriber.emit (OperatorMerge.java:521)
at rx.internal.operators.OperatorMerge$InnerSubscriber.onError (OperatorMerge.java:808)
at rx.Observable$ThrowObservable.call (Observable.java:9600)
at rx.Observable$ThrowObservable.call (Observable.java:9590)
at rx.Observable.unsafeSubscribe (Observable.java:7710)
at rx.internal.operators.OperatorMerge$MergeSubscriber.onNext (OperatorMerge.java:231)
at rx.internal.operators.OperatorMerge$MergeSubscriber.onNext (OperatorMerge.java:140)
at rx.internal.operators.OperatorMap.onNext (OperatorMap.java:55)
at retrofit.RxJavaCallAdapterFactory$CallOnSubscribe.call (RxJavaCallAdapterFactory.java:113)
at retrofit.RxJavaCallAdapterFactory$CallOnSubscribe.call (RxJavaCallAdapterFactory.java:88)
at rx.Observable.call (Observable.java:162)
at rx.Observable.call (Observable.java:154)
at rx.Observable.call (Observable.java:162)
at rx.Observable.call (Observable.java:154)
at rx.Observable.call (Observable.java:162)
at rx.Observable.call (Observable.java:154)
at rx.Observable.unsafeSubscribe (Observable.java:7710)
at rx.internal.operators.OperatorSubscribeOn.call (OperatorSubscribeOn.java:62)
at rx.internal.schedulers.ScheduledAction.run (ScheduledAction.java:55)
at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:422)
at java.util.concurrent.FutureTask.run (FutureTask.java:237)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access1 (ScheduledThreadPoolExecutor.java:152)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run (ScheduledThreadPoolExecutor.java:265)
at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:587)
at java.lang.Thread.run (Thread.java:818)
Thanks,
Anton
谢谢，
安东
回答by Jake Wharton
From the stack trace,
从堆栈跟踪中，
at rx.internal.operators.OperatorSingle$ParentSubscriber.onCompleted (OperatorSingle.java:131)
at rx.internal.operators.OperatorTake.onCompleted (OperatorTake.java:53)
This equates to take(1).single()which is also the first()convenience operator. I suspect you are using the latter, but both require at least one element.
这等同于take(1).single()which 也是first()便利运算符。我怀疑您正在使用后者，但两者都至少需要一个元素。
By using empty(), you are creating an observable with no elements which violates the contract of the downstream operators. Either emit a default item in the onErrorResumeNextobservable or change your downstream code to support streams with no elements.
通过使用empty()，您将创建一个没有违反下游运营商合同的元素的 observable。要么在onErrorResumeNextobservable 中发出一个默认项，要么更改您的下游代码以支持没有元素的流。
