stream - 通过 WCF 流式传输文件时出现 ArgumentNullException

Question

我有一个 WCF 流式二进制文件。以下是契约(Contract)的简短版本。

[MessageContract()]
public class DocumentTransfer
{
    [MessageHeader(MustUnderstand = true)]
    public string Title { get; set; }

    [MessageHeader(MustUnderstand = true)]
    public string FileName { get; set; }

    [MessageBodyMember(Order = 1)]
    public System.IO.Stream Data;
}

一切正常，但在某些情况下，只需要更新与文件关联的一些其他值，而不需要更新文件本身。在这种情况下，客户端设置 Data = null。然后 Data 属性无法被解释/序列化并抛出此异常:

System.ServiceModel.Dispatcher.StreamFormatter.Serialize(XmlDictionaryWriter writer, Object[] parameters, Object returnValue)
System.ServiceModel.Dispatcher.OperationFormatter.SerializeBodyContents(XmlDictionaryWriter writer, MessageVersion version, Object[] parameters, Object returnValue, Boolean isRequest)
System.ServiceModel.Dispatcher.OperationFormatter.OperationFormatterMessage.OperationFormatterBodyWriter.OnWriteBodyContents(XmlDictionaryWriter writer)
System.ServiceModel.Channels.BodyWriter.WriteBodyContents(XmlDictionaryWriter writer)
System.ServiceModel.Channels.BodyWriterMessage.OnWriteBodyContents(XmlDictionaryWriter writer)
System.ServiceModel.Channels.Message.OnWriteMessage(XmlDictionaryWriter writer)
System.ServiceModel.Channels.Message.WriteMessage(XmlDictionaryWriter writer)
System.ServiceModel.Channels.TextMessageEncoderFactory.TextMessageEncoder.WriteMessage(Message message, Stream stream)
System.ServiceModel.Channels.HttpOutput.WriteStreamedMessage(TimeSpan timeout)
System.ServiceModel.Channels.HttpOutput.Send(TimeSpan timeout)
System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelRequest.SendRequest(Message message, TimeSpan timeout)
System.ServiceModel.Channels.RequestChannel.Request(Message message, TimeSpan timeout)
System.ServiceModel.Dispatcher.RequestChannelBinder.Request(Message message, TimeSpan timeout)
System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs)
System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)
System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)
System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
...UploadDocument(DocumentTransfer request)
...UploadDocument(DocumentTransfer request) in ...

大家有什么想法吗？

Answer 1

当正文为空时，您会在 SerializeBodyContents 中收到错误。

您可以在没有文件时创建不同的操作，或者在流中放入一个字节以避免异常。如果您无法更改契约(Contract)，则最好选择第一个选项，最后一个选项更可取。