Type 'System.IO.FileStream' with data contract name 'FileStream:http://schemas.datacontract.org/2004/07/System.IO' is not expected.

今天在WCF项目里使用DataContract序列化接口参数的时候，报了这个错，错误详细信息如下：

System.ServiceModel.CommunicationException: There was an error while trying to serialize parameter http://tempuri.org/:reqDTO. The InnerException message was 'Type 'System.IO.FileStream' with data contract name 'FileStream:http://schemas.datacontract.org/2004/07/System.IO' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.'.  Please see InnerException for more details. ---> System.Runtime.Serialization.SerializationException: Type 'System.IO.FileStream' with data contract name 'FileStream:http://schemas.datacontract.org/2004/07/System.IO' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.

然后我就百度了一下，发现国外有个小哥也遇到相同的问题，别人给他的解释是：

DataContract messages serialize in a different way than MessageContract messages. Having a Stream member (thus allowing streaming) must be done using MessageContract, wcf then understands it is inteded for streaming and does not try to perform standard serialization.

意思是说DataContract序列化的方式和MessageContract消息序列化的方式不一样，如果你的WCF接口参数里包含有Stream（流类型），就必须用MessageContract。