情况是SingleRoom和DoubleRoom是Room类的子类。在WebService中有一个方法是返回Room类。

public Room Get(int roomId)

{

    return Room.Get(roomId);

}

XmlSerializer在序列化时只能识别父类，而不能识别子类，所以导致序列化的错误。需要将[XmlInclude(typeof(SingleRoom))]和[XmlInclude(typeof(DoubleRoom))]同时加到WebService中。

[XmlInclude(typeof(SingleHouse))]

[XmlInclude(typeof(DoubleHouse))]

public class RoomService : System.Web.Services.WebService