序列化系统对象

Question

I'm trying to create a webservice to return a generic. The return class looks like this:

[Serializable]
public class RenderReturn
{
    public RenderReturnStatus StatusReturn { get; set; }
    public string MessageReturn { get; set; }
    public string MessageTitle { get; set; }
    public object **ObjectReturn** { get; set; }
}

Where ObjectReturn can be an object or a list of application objects, like cars, customers, etc..

But the webservice returns the following error:

System.InvalidOperationException: There was an error generating the XML document. --->
System.InvalidOperationException: The type Environment was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically.
   at System.Xml.Serialization.XmlSerializationWriter.WriteTypedPrimitive(String name, String ns, Object o, Boolean xsiType)

This is possible or method should always return specific types?

Answer 1

Explicitly name your types. Otherwise one can put something in that isn't serializable.

Answer 2

Type of object is too generic for .NET to know what kind of object it is dealing with and how to deserialise. So it asks you to give it some hint by using XmlInclude attributes telling .NET the types to expect. In WCF you do the same: you use KnownType attribute to decorate properties.

Type object is not a good candidate for DTO objects that need to cross process boundaries.

In WCF or Web Services, try not to think in object-oriented fashion but think in WSDL. As far as WSDL is concerned you have a contract which explicitly defines the type of messages passed between client and server.

Answer 3

Try something along these lines:

public class RenderReturn<T>
{
  public T ObjectReturn {get;set;}
}

That way, at run-time, you'll have a concrete type rather than just System.Object.