deserialize SortedSet : why items need to implement IComparable? - c#-4.0

Question

I have de folowing classes :
[DataContract]
public class MyProject
{
[DataMember(Name = "Branches")]
private SortedSet<ModuleFilter> branches = new SortedSet<ModuleFilter>(new ModuleFilterComparer());
[DataMember(Name="VbuildFilePath")]
private string buildprogram = null;
}
I can serialize it to a file with :
DataContractSerializer x = new DataContractSerializer(p.GetType());
using (System.Xml.XmlWriter writer = System.Xml.XmlWriter.Create(p.GetFilePath()))
{
x.WriteObject(writer, p);
}
But when I try to read it back with the folowing piece of code, it fails unless I add a dummy implementation of IComparable to the ModuleFilter object
DataContractSerializer x = new DataContractSerializer(typeof(MyProject));
using (System.Xml.XmlReader reader = System.Xml.XmlReader.Create(filePath))
{
p = (MyProject)x.ReadObject(reader);
}
Why does not the deserializer use the provided IComparer of the SortedSet member ?
Thank you

Answer 1

It is because DataContractSerializer uses default constructor of SortedSet to initialize field.
Solution 1: recreate field after deserialization with needed comparer
[DataContract]
public class MyProject : IDeserializationCallback
{
//...
void IDeserializationCallback.OnDeserialization(Object sender)
{
branches = new SortedSet<ModuleFilter>(branches, new ModuleFilterComparer());
}
}
Solution 2: use your own sorted set implementation instead of SortedSet<ModuleFilter>
public class ModuleFilterSortedSet : SortedSet<ModuleFilter>
{
public ModuleFilterSortedSet()
: base(new ModuleFilterComparer())
{
}
public ModuleFilterSortedSet(IComparer<ModuleFilter> comparer)
: base(comparer)
{
}
}