RxJava序列不包含元素错误

我正在使用RxJava，除了在引发这些错误的情况下，一切看起来都不错。RxJava序列不包含元素错误

Caused by: java.util.NoSuchElementException: Sequence contains no elements 
at rx.internal.operators.OperatorSingle$ParentSubscriber.onCompleted(OperatorSingle.java:118) 
at rx.internal.operators.OperatorTake$1.onCompleted(OperatorTake.java:56) 
at rx.internal.operators.OnSubscribeFilter$FilterSubscriber.onCompleted(OnSubscribeFilter.java:99) 
at rx.internal.operators.OnSubscribeFromIterable$IterableProducer.slowpath(OnSubscribeFromIterable.java:134) 
at rx.internal.operators.OnSubscribeFromIterable$IterableProducer.request(OnSubscribeFromIterable.java:89) 
at rx.internal.operators.OperatorTake$1$1.request(OperatorTake.java:109) 
at rx.Subscriber.setProducer(Subscriber.java:211) 
at rx.internal.operators.OperatorTake$1.setProducer(OperatorTake.java:93) 
at rx.internal.operators.OnSubscribeFilter$FilterSubscriber.setProducer(OnSubscribeFilter.java:104) 
at rx.internal.operators.OnSubscribeFromIterable.call(OnSubscribeFromIterable.java:63) 
at rx.internal.operators.OnSubscribeFromIterable.call(OnSubscribeFromIterable.java:34) 
at rx.Observable.unsafeSubscribe(Observable.java:10211) 
at rx.internal.operators.OnSubscribeFilter.call(OnSubscribeFilter.java:45) 
at rx.internal.operators.OnSubscribeFilter.call(OnSubscribeFilter.java:30) 
at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48) 
at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30) 
at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48) 
at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30) 
at rx.Observable.unsafeSubscribe(Observable.java:10211) 
at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:48) 
at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:33) 
at rx.Observable.unsafeSubscribe(Observable.java:10211) 
at rx.internal.operators.OperatorMerge$MergeSubscriber.onNext(OperatorMerge.java:250) 
at rx.internal.operators.OperatorMerge$MergeSubscriber.onNext(OperatorMerge.java:147) 
at rx.internal.operators.OnSubscribeMap$MapSubscriber.onNext(OnSubscribeMap.java:77) 
at rx.internal.operators.OperatorMerge$MergeSubscriber.emitScalar(OperatorMerge.java:399) 
at rx.internal.operators.OperatorMerge$MergeSubscriber.tryEmit(OperatorMerge.java:357) 
at rx.internal.operators.OperatorMerge$InnerSubscriber.onNext(OperatorMerge.java:852) 
at rx.internal.operato

编辑：的问题是在功能NumberObservables::mergeNumberAndName，

public static Observable<Trailer> mergeTrailerType(Trailer trailer) { 
    String id = number.getId(); 
    return Observable.from(Store.names()) 
      .first(name -> id.equals(name.getId())) 
      .map(name -> { 
       number.setName(name); 
       return number; 
      }); 
}

，我可以看到first使得问题，但我不能与采取更换（1）或firstOrDefault（找不到getId()）。它可以与single一起使用吗？你可能在流（NumberObservables::getByNumber或NumberObservables::mergeNumberAndName）的single()操作某处申请

来源

2017-06-21 Claire

，它可以在堆栈跟踪这里可以观察到：

at rx.internal.operators.OperatorSingle$ParentSubscriber.onCompleted(OperatorSingle.java:118)

single()预计来源Observable发射只有一个项目，并通知错误的NoSuchElementException如果源可观察到发射没有任何项目，从堆栈跟踪，这可能是发生由于一些过滤器已应用于：

at rx.internal.operators.OnSubscribeFilter$FilterSubscriber.onCompleted(OnSubscribeFilter.java:99)

来源

2017-06-21 10:55:48 yosriz

是的，我发现它现在，我在'NumberObservables :: mergeNumberAndName'中应用'.first'操作符，这就是为什么它会抛出异常。你知道我该如何解决它？ – Claire

好吧，很难说不理解你的逻辑，你可以使用'firstOrDefault'来提供默认值，但是通常你想从Observable中获得单个项目，而不是这样，所以你的逻辑要根据你期望的来完善在这种情况下发出 – yosriz

我用函数NumberObservables :: mergeNumberAndName和其他细节改变了这个问题。你可以看到。 – Claire

RxJava序列不包含元素错误

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