How to serialize properties with DefaultValueAttribute using XmlSerializer?

Question

I am using XmlSerializer to serialize C# objects to XML. I have DefaultValueAttribute on some of the properties of the classes I am trying to serialize, when I try to serialize them it seems that XmlSerializer does not include value in xml if it equals default value. Look at this example:

using System.IO;
using System.Xml;
using System.Xml.Serialization;

namespace Test
{
    public class Person
    {
        [System.Xml.Serialization.XmlAttribute()]
        [System.ComponentModel.DefaultValue("John")]
        public string Name { get; set; }
    }

    public static class Test
    {
        public static void Main()
        {
            var serializer = new XmlSerializer(typeof(Person));
            var person = new Person { Name = "John" };

            using (var sw = new StringWriter())
            {
                using (var writer = XmlWriter.Create(sw))
                {
                    serializer.Serialize(writer, person);
                    var xml = sw.ToString();
                }
            }
        }
    }
}

It will produce the following xml (notice name attribute is not available):

<?xml version="1.0" encoding="utf-16"?>
<Person xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" />

I cannot modify the source code of the classes so I CANNOT remove DefaultValueAttribute. Is there a way to make XmlSerializer serialize this properties without changing the source code?

Answer 1

I dont have enough reputation to comment on steve16351's answer. but I feel I improved upon his code a little bit.

My use case involved an XML schema file generated via XSD.exe provided by Microsoft, and a class was then generated from the schema file. So the class had all the DefaultValue tags on it from the schema. There was also many nested types created. So to make my code succinct, I modified the 'Generate' method to get the overrides for the top-level class, and all the ones beneath it. Then everything is returned in a single XmlAttributesOverrides object.

static XmlAttributeOverrideGenerator()
{
    _overrides = Generate(typeof(T), new XmlAttributeOverrides());
}

private static XmlAttributeOverrides Generate(Type targetType, XmlAttributeOverrides Overrides)
{
    foreach (var property in targetType.GetProperties())
    {
        if (property.CustomAttributes.Any( CA => CA.AttributeType == typeof(DefaultValueAttribute)))
        {
            XmlAttributes propertyAttributes = new XmlAttributes(new CustomAttribProvider(property, _ignoreAttributes));
            Overrides.Add(targetType, property.Name, propertyAttributes);
        }
        else
        {
            Type propType = property.PropertyType;
            if (propType.IsClass && !propType.IsValueType && !propType.IsEnum && !propType.IsPrimitive && !propType.IsSealed)  // Check if this is a custom class
            {
                //If this is a nested class or other class type, generate its overrides as well
                Generate(propType, Overrides);
            }
        }
    }

    return Overrides;
}