RxJava序列不包含元素錯誤

我正在使用RxJava，除了在引發這些錯誤的情況下，一切看起來都不錯。RxJava序列不包含元素錯誤

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

編輯：的問題是在功能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使得問題，但我不能與採取更換（1）或firstOrDefault（找不到getId()）。它可以與single一起使用嗎？你可能在流（NumberObservables::getByNumber或NumberObservables::mergeNumberAndName）的single()操作某處申請

來源

2017-06-21 Claire

，它可以在堆棧跟蹤這裏可以觀察到：

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

single()預計來源Observable發射只有一個項目，並通知錯誤的NoSuchElementException如果源可觀察到發射沒有任何項目，從堆棧跟蹤，這可能是發生由於一些過濾器已應用於：

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

來源

2017-06-21 10:55:48 yosriz

是的，我發現它現在，我在'NumberObservables :: mergeNumberAndName'中應用'.first'操作符，這就是爲什麼它會拋出異常。你知道我該如何解決它？ – Claire

好吧，很難說不理解你的邏輯，你可以使用'firstOrDefault'來提供默認值，但是通常你想從Observable中獲得單個項目，而不是這樣，所以你的邏輯要根據你期望的來完善在這種情況下發出 – yosriz

我用函數NumberObservables :: mergeNumberAndName和其他細節改變了這個問題。你可以看到。 – Claire

RxJava序列不包含元素錯誤

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