通过WCF流传输文件时出现的“ArgumentNullException”错误

Question

我有一个WCF流式传输二进制文件。以下是合同的缩短版。

[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;
}

一切都运行良好，但是有些情况下只需要更新与文件相关的其他值，而不是文件本身。在这种情况下，客户端将Data设置为null。然后无法解释/序列化Data属性，从而引发此异常：

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 ...

有什么想法吗？

- David

---

使用另一种类型，比如DocumentMetadataTransfer。这是有道理的，因为正如你所解释的那样，它们适用于不同的目的。仅带有标题的消息并不完全是一条消息，对吧？此外，Title和FileName不应该是MessageHeader项，因为它们实际上是消息的一部分，而不一定是消息元数据，而是操作数据。 - Grant Thomas

Answer 1

当body为空时，您会在SerializeBodyContents中遇到错误。

您可以为没有文件的情况创建不同的操作，或者在流中放入一个字节以避免异常。如果您无法更改合同，则最好选择前面的选项，否则选择后面的选项。

- Shiraz Bhaiji

Answer 2

另一个选择是返回Stream.Null。

- Matthew Cole