Why isn't possible to serialize into a Xml File an interface like IList?

Question

I'm trying to serialize into a Xml File an object which is declared as ILIst, but it's an instance of List. The exception tells me the reason: You can't serialize an interface.

This is really necessary in my design, or what other way do I have to serialize it?

Answer 1

You have to know what concrete type to instantiate.

The serializer has to go by the metadata, not runtime type. If all you knew was that your target object had to implement IList, what would you construct? There not necessarily even a class that implements it.

Answer 2

This should not be a problem, you can always use object.GetType(). Here's an example:

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

class Program {
    static void Main(string[] args) {
        System.Collections.IList list = new List<int> { 1, 2, 3 };
        var ser = new XmlSerializer(list.GetType());
        ser.Serialize(Console.Out, list);
        Console.ReadLine();
    }
}

Answer 3

I suppose the reason you need to keep the design with IList is because it's a common interface to other module. One possible solution:

Instead of:

    [XmlElement("Test")]
    public IList<String> Tests
    {
        get;
        set;
    }

You can probably try:

    [XmlElement("Test")]
    public List<String> TestList
    {
        get;
        set;
    }

    [XmlIgnore]
    public IList<String> Tests
    {
        get { return TestList; }
    }

This way you can keep the same interface, and meanwhile take advantage of serialize/deserialize functionality in .Net Xml library.

Answer 4

I can see two options:

1. You can cast it back to List before when passing it to the serializer. Not ideal, but it would work.
2. You iterate over the IList and serialize each item to the same stream independently.

Answer 5

You can't serialize an interface because it doesn't contains any data. May be the best you can do is to implement ISerializable to control the serialization yourself.