How to serialize XML array/list as sequentially named elements

Question

I need help serializing XML in C#/.net.

Given something like this in C#:

public class Action {
    public string Name;
    public string Type;
}

public class TestObject {
    public List<Action> Actions;
}

I want to serialize the list of actions as elements, each with a unique name:

<TestObject>
    <Action0>
        <Name>A</Name>
        <Type>Dog</Name>
    </Action0>
    <Action1>...</Action1>
    <Action2>...</Action2>
    ...
</TestObject>

I've been looking into using IXmlSerializable on a custom List object to replace TestObject. But I'm not sure how to proceed.

Is this on the right track?

public class ActionCollection<T> : List<T>, IXmlSerializable ...

public class TestObject : ActionCollection<Action> { ...

The other possibility that comes to mind is - some way to customize the serialization of each Action to override the element name using C# code that could add the digit?

Why? This looks like an xy problem. What's the motivation for naming each Action element differently, when they are stored in a list? — Ondrej Tucny
– Ondrej Tucny, Commented May 18, 2020 at 15:41
Great question! This is the export format required. I didn't define it and can't change it - just need to produce the expected output. I can change the C# code of how I store it - but the output has to have those "sequential" names. — Daniel Jones
– Daniel Jones, Commented May 18, 2020 at 15:43

jdweng · Accepted Answer · 2020-05-18 16:56:20Z

Using Xml Linq :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Xml;
using System.Xml.Linq;

namespace ConsoleApplication1
{
    class Program
    {
        const string FILENAME = @"c:\temp\test.xml";
        static void Main(string[] args)
        {
            TestObject tests = new TestObject() {
                Actions = new List<Action>() {
                    new Action() { Name = "A", Type = "Dog"},
                    new Action() { Name = "C", Type = "Cat"},
                    new Action() { Name = "E", Type = "Elephant"}
                    }
            };

            string root = "<TestObject></TestObject>";

            XDocument doc = XDocument.Parse(root);
            XElement testObject = doc.Root;

            int index = 0;
            foreach (Action action in tests.Actions)
            {
                XElement newAction = new XElement("Action" + index.ToString(), new object[] {
                    new XElement("Name", action.Name),
                    new XElement("Type", action.Type)
                });
                testObject.Add(newAction);
                index++;
            }

            doc.Save(FILENAME);

        }
    }
    public class Action
    {
        public string Name;
        public string Type;
    }

    public class TestObject
    {
        public List<Action> Actions;
    }
}

Using a Custom Xml Serializer

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Xml;
using System.Xml.Linq;
using System.Xml.Serialization;
using System.Xml.Schema;

namespace ConsoleApplication1
{
    class Program
    {
        const string FILENAME = @"c:\temp\test.xml";
        static void Main(string[] args)
        {
            TestObject tests = new TestObject() {
                Actions = new List<Action>() {
                    new Action() { Name = "A", Type = "Dog"},
                    new Action() { Name = "C", Type = "Cat"},
                    new Action() { Name = "E", Type = "Elephant"}
                    }
            };

            XmlWriterSettings settings = new XmlWriterSettings();
            settings.Indent = true;
            XmlWriter writer = XmlWriter.Create(FILENAME,settings);

            XmlSerializer serializer = new XmlSerializer(typeof(TestObject));
            serializer.Serialize(writer, tests);

        }
    }
    public class Action
    {
        public string Name;
        public string Type;
    }

    public class TestObject : IXmlSerializable
    {
        public List<Action> Actions;

        public void WriteXml(XmlWriter writer)
        {
            List<XElement> testObjects = new List<XElement>();

            int index = 0;
            foreach (Action action in Actions)
            {
                XElement newAction = new XElement("Action" + index.ToString(), new object[] {
                    new XElement("Name", action.Name),
                    new XElement("Type", action.Type)
                });
                testObjects.Add(newAction);
                index++;
            }
            string obj = string.Join("", testObjects.Select(x => x.ToString()));
            writer.WriteRaw("\n" + obj + "\n");

        }
        public void ReadXml(XmlReader reader)
        {

        }

        public XmlSchema GetSchema()
        {
            return (null);
        }
    }
}

I like this approach, but it would require rebuilding the whole XML tree (I left out that each "Action" is a fairly large object with nested child objects).
I created a custom serializer class. See modification above.
Thank you, @jdweng. Your simple example of IXmlSerializable was perfect!

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