c# - How to tell XmlSerializer to serialize properties with [DefautValue(...)] always?

Question

I am using DefaultValue attribute for the proper PropertyGrid behavior (it shows values different from default in bold). Now if I want to serialize shown object with the use of XmlSerializer there will be no entries in xml-file for properties with default values.

What is the easiest way to tell XmlSerializer to serialize these still?

I need that to support "versions", so when I change default value later in the code - serialized property gets value it had serialized with, not "latest" one. I can think about following:

• Override behavior of PropertyGrid (use custom attribute, so it will be ignoreed by XmlSerializer);
• Do sort of a custom xml-serialization, where ignore DefaultValue's;
• Do something with object before passing it to XmlSeriazer so it won't contain DefaultValue's anymore.

But there is a chance I miss some secret property what allows to do it without much pain =D.

Here is an example of what I want:

    private bool _allowNegative = false;
    /// <summary>
    /// Get or set if negative results are allowed
    /// </summary>
    [Category(CategoryAnalyse)]
    [Admin]
    [TypeConverter(typeof(ConverterBoolOnOff))]
    //[DefaultValue(false)] *1
    public bool AllowNegative
    {
        get { return _allowNegative; }
        set
        {
            _allowNegative = value;
            ConfigBase.OnConfigChanged();
        }
    }
    //public void ResetAllowNegative() { _allowNegative = false; } *2
    //public bool ShouldSerializeAllowNegative() { return _allowNegative; } *3
    //public bool ShouldSerializeAllowNegative() { return true; } *4

If I uncomment (*1), then I have desired effect in PropertyGrid - properties with default values are displayed in normal text, otherwise text is bold. However XmlSerializer will NOT put properties with default value into xml-file and this is BAD (and I am trying to fix it).

If I uncomment (*2) and (*3), then it's totally same as uncommenting (*1).

If I uncomment (*2) and (*4), then XmlSerializer will always put properties into xml-file, but this happens because they do not have default value anymore and PropertyGrid shows all values in bold text.

Answer 1

As long as you don't need attributes in your Xml, if you use the DataContractSerializer instead you will get the behavior you desire.

[DataContract]
public class Test
{
    [DataMember]
    [DefaultValue(false)]
    public bool AllowNegative { get; set; }
}

void Main()
{
    var sb2 = new StringBuilder();
    var dcs = new DataContractSerializer(typeof(Test));

    using(var writer = XmlWriter.Create(sb2))
    {
        dcs.WriteObject(writer, new Test());
    }

    Console.WriteLine(sb2.ToString());  
}

produces (minus namespaces etc)

<Test>
    <AllowNegative>false</AllowNegative>
</Test>