How do I XML Serialize a object without a parameter-less constructor?

Question

I am trying to use the Application Settings feature of Visual Studios to easy save the setting of my program. One of the class I am trying to serialize contains a number of DenseMatrix objects from the MathNet.Numerics library. The DenseMatrix class does not have a parameter-less constructor so when calling My.Settings.Save() the serialization would crash. I tried replacing the matrices with a Double(,) but that crashed as well. I then tried writing some code to wrap a DenseMatrix as follows but it also failed I am guessing because all the bases classes have to have parameter-less constructors but I am not sure. Is there another logical way to store the matrices that can be automatically serialized by My.Settings.Save?

 <SettingsSerializeAs(SettingsSerializeAs.Xml)>
 Public Class AvtMatrix
    Inherits DenseMatrix
    Public Sub New()
       My.Base.New(3,3)
    End Sub
  End Class

Answer 1

Digging into some of the IL, it looks like this uses XmlSerializer - in which case, the only answer is: you can't - it demands a public parameterless constructor. You can cheat a little , though - with [Obsolete] ; this works, for example:

using System;
using System.IO;
using System.Xml.Serialization;
public class Foo
{
    public string Bar { get; set; }
    public Foo(string bar)
    {
        Bar = bar;
    }
    [Obsolete("You don't look like a serializer", true)]
    public Foo()
    {
    }
}
class Program
{
    static void Main()
    {
        var ser = new XmlSerializer(typeof(Foo));
        using (var ms = new MemoryStream())
        {
            ser.Serialize(ms, new Foo("abc"));
            ms.Position = 0;
            Foo clone = (Foo)ser.Deserialize(ms);
            Console.WriteLine(clone.Bar); // "abc"
        }
    }
}