Using XmlSerializer to serialize derived classes

Question

I'm using XmlSerializer to serialize an object that contains a generic list

List <ChildBase> Children {get;set}

The problem is that each element derives from ChildBase which in fact is an abstract class. When I try to deserialize, I get an invalidOperationException

Is there a way I can use XmlSerializer with derived objects?

Answer 1

There are three ways of doing this; either you can use [XmlInclude] against the type, or you can use XmlElement/XmlArrayItem against the property. They are all shown below; uncomment the pair you prefer:

using System;
using System.Collections.Generic;
using System.Xml.Serialization;
public class MyWrapper {
    //2: [XmlElement("A", Type = typeof(ChildA))]
    //2: [XmlElement("B", Type = typeof(ChildB))]
    //3: [XmlArrayItem("A", Type = typeof(ChildA))]
    //3: [XmlArrayItem("B", Type = typeof(ChildB))]
    public List<ChildClass> Data { get; set; }
}
//1: [XmlInclude(typeof(ChildA))]
//1: [XmlInclude(typeof(ChildB))]
public abstract class ChildClass {
    public string ChildProp { get; set; }
}
public class ChildA : ChildClass {
    public string AProp { get; set; }
}
public class ChildB : ChildClass {
    public string BProp { get; set; }
}
static class Program {
    static void Main() {
        var ser = new XmlSerializer(typeof(MyWrapper));
        var obj = new MyWrapper {
            Data = new List<ChildClass> {
                new ChildA { ChildProp = "abc", AProp = "def"},
                new ChildB { ChildProp = "ghi", BProp = "jkl"}}
        };
        ser.Serialize(Console.Out, obj);
    }
}