Xml-serilizing with interfaces

[grignard]

A list of interfaces which is implemented by an abstract klass with two subclasses that need to be serialised. I have no idea how to do this since interfaces can not be serialised as I understand it.
My code generates the error message:

Cannot serialize interface ConsoleApplication4.Creature_interface.


..allthough Im not trying to serilize the interfaces themselves.

Which is the right way to deal with a problem like this? Is there any stright
way to deal with this problem or is there some kind of workaround needed?





using System;
using System.Collections.Generic;
using System.Text;
using UtilitiesLibrary;
using System.Xml.Serialization;

namespace ConsoleApplication4
{
class Program
{
static void Main(string[] args)
{
Cat cat1 = new Cat("Knut", 6);
Dog dog1 = new Dog("Bertil", 5);

List<Creature_interface> Animallist = new List<Creature_interface>();
Animallist.Add(cat1);
Animallist.Add(dog1);

UniversalSerializer.XMLSerialize("filename.xml", Animallist);
Console.ReadLine();

}
}

public interface Creature_interface
{
string Name { get;}
int Age { get; }
}

public abstract class Creature : Creature_interface
{
string _name;
int _age;

public Creature(string name, int age )
{
_name = name;
_age = age;
}

public Creature()
{ }

public string Name
{
get { return _name; }
set { _name = value; }
}

public int Age
{
get { return _age; }
set { _age = value; }
}

public abstract void Speak();
}

[Serializable]
public class Dog:Creature
{
public Dog
(string _name, int _age): base (_name, _age)
{ }

public Dog { }

public override void Speak()
{
Console.WriteLine("Bark Bark");
}
}

[Serializable]
public class Cat:Creature
{
public Cat
(string _name, int _age): base (_name, _age)
{ }

public Cat { }



public override void Speak()
{
Console.WriteLine("Mjau Mjau");
}
}

}


using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Xml.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

namespace UtilitiesLibrary
{
public class UniversalSerializer
{

public static void XMLSerialize<T>(string filename, T objectToSerialize)
{
XmlSerializer Serializer = new XmlSerializer(typeof(List<Creature_interface>), new Type[] {typeof(Dog), typeof(Cat)});

Stream fStream = new FileStream(filename, FileMode.Create,
FileAccess.Write, FileShare.None);

Serializer.Serialize(fStream, objectToSerialize);
fStream.Close();
}
//more methods...
}
}


Thank you for any help.

[Thread1]

since interface cannot be serialized, have you ever tried the base class - List<Creature>?? think it should work. furthermore, you must add a parameterless constructor to your Dog and Cat class.