Use the XmlInclude or SoapInclude attribute to specify types that are not known statically

Question

I ve got a very strange problem when working with  NET s XmlSerializer    Take the following example classes   public class Order        public PaymentCollection Payments   get  set           everything else is serializable  including other collections of non-abstract types     public class PaymentCollection   Collection lt Payment gt       public abstract class Payment          abstract methods    public class BankPayment   Payment         method implementations     AFAIK  there are three different methods to solve the InvalidOperationException that s caused by the serializer not knowing about the derived types of Payment   1  Adding XmlInclude to the Payment class definition   This is not possible due to all classes being included as external references over which I have no control of   2  Passing the derived types  types during creation of the XmlSerializer instance  Doesn t work   3  Defining XmlAttributeOverrides for the target property in order to override the property s default serialization  as explained in this SO post   Also doesn t work  XmlAttributeOverrides initialization follows    Type bankPayment   typeof BankPayment    XmlAttributes attributes   new XmlAttributes    attributes XmlElements Add new XmlElementAttribute bankPayment Name  bankPayment     XmlAttributeOverrides overrides   new XmlAttributeOverrides    overrides Add typeof Order    Payments   attributes     The appropriate XmlSerializer constructor would then be used   NOTE  by doesn t work I mean the InvalidOperationException  BankPayment was not expected     is thrown   Can anyone shed some light on the subject  How would one go about and debug the issue further

User · Answer

I agree with bizl    XmlInclude typeof ParentOfTheItem     Serializable  public abstract class WarningsType      also if you need to apply this included class to an object item you can do like that   System Xml Serialization XmlElementAttribute  Warnings   typeof WarningsType    public object   Items       get               return this itemsField            set               this itemsField   value

User · Answer

Base on this I was able to solve this by changing the constructor of XmlSerializer I was using instead of changing the classes   Instead of using something like this  suggested in the other answers     XmlInclude typeof Derived    public class Base     public class Derived   Base     public void Serialize         TextWriter writer   new StreamWriter SchedulePath       XmlSerializer xmlSerializer   new XmlSerializer typeof List lt Derived gt         xmlSerializer Serialize writer  data       writer Close        I did this   public class Base     public class Derived   Base     public void Serialize         TextWriter writer   new StreamWriter SchedulePath       XmlSerializer xmlSerializer   new XmlSerializer typeof List lt Derived gt    new     typeof Derived          xmlSerializer Serialize writer  data       writer Close

User · Answer

Just do it in the Base  that way any child can be Serialized  less code cleaner code   public abstract class XmlBaseClass       public virtual string Serialize           this SerializeValidation         XmlSerializerNamespaces XmlNamespaces   new XmlSerializerNamespaces new     XmlQualifiedName Empty         XmlWriterSettings XmlSettings   new XmlWriterSettings             Indent   true        OmitXmlDeclaration   true             StringWriter StringWriter   new StringWriter         XmlSerializer Serializer   new XmlSerializer this GetType         XmlWriter XmlWriter   XmlWriter Create StringWriter  XmlSettings       Serializer Serialize XmlWriter  this  XmlNamespaces       StringWriter Flush        StringWriter Close         return StringWriter ToString            protected virtual void SerializeValidation          XmlRoot ElementName    MyRoot   Namespace    MyNamespace    public class XmlChildClass   XmlBaseClass     protected override void SerializeValidation             Add custom validation logic here or anything else you need to do         This way you can call Serialize on the child class no matter the circumstance and still be able to do what you need to before object Serializes

User · Answer

Just solved the issue  After digging around for a while longer  I found this SO post which covers the exact same situation  It got me in the right track   Basically  the XmlSerializer needs to know the default namespace if derived classes are included as extra types  The exact reason why this has to happen is still unknown but  still  serialization is working now

User · Answer

This worked for me    XmlInclude typeof BankPayment     Serializable  public abstract class Payment           Serializable  public class BankPayment   Payment       Serializable  public class Payments   List lt Payment gt     XmlSerializer serializer   new XmlSerializer typeof Payments   new Type   typeof Payment

[c#] Use the XmlInclude or SoapInclude attribute to specify types that are not known statically

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