using System;

using System.IO;

using System.Xml.Serialization;

​

public class MyClass

{

    [Obsolete("This property is obsolete. Use MyNewProperty instead.")]

    public string MyObsoleteProperty { get; set; }

}

​

public class Program

{

    public static void Main()

    {

        var myObj = new MyClass

        {

            MyObsoleteProperty = "Some value"

        };

​

        var overrides = new XmlAttributeOverrides();

        var attributes = new XmlAttributes { XmlIgnore = false };

        overrides.Add(typeof(MyClass), nameof(MyClass.MyObsoleteProperty) , attributes);

​

        var serializer = new XmlSerializer(typeof(MyClass), overrides);

        // serialize to file...

        using (var writer = new StreamWriter("data.xml"))

        {

            serializer.Serialize(writer, myObj);

        }

​

        // deserialize

        MyClass deserializedObj;

        using (var reader = new StreamReader("data.xml"))

        {

            deserializedObj = (MyClass)serializer.Deserialize(reader);

        }

​

        // deprecated property still has value

        Console.WriteLine(deserializedObj.MyObsoleteProperty);

    }

}

​