How to Serialize class derived from ReadOnlyCollection

Question

When I try to serialize my own class that is derived from ReadOnlyCollection I get the error:

Type 'MyReadOnlyCollection`1[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]' with CollectionDataContractAttribute attribute is an invalid collection type since it does not have a default constructor.

Now the error makes sense, it's true I do not have a default constructor. However I am able to Serialize a ReadOnlyCollection using the DataContractSerializer even though ReadOnlyCollection does not have a parameterless default constructor.

// OK
ReadOnlyCollection<string> readOnlyCollection = new ReadOnlyCollection<string>(new List<string> { "a", "b", "c" });
string result1 = Serialize(readOnlyCollection);

// Throws InvalidDataContractException
MyReadOnlyCollection<string> myReadOnlyCollection = new MyReadOnlyCollection<string>(new List<string> { "a", "b", "c" });
string result2 = Serialize(myReadOnlyCollection);

public static string Serialize(object o)
{
    var serializer = new DataContractSerializer(o.GetType());
    var stringBuilder = new StringBuilder();

    using (XmlWriter xmlWriter = XmlWriter.Create(stringBuilder))
    {
        serializer.WriteObject(xmlWriter, o);
    }

    return stringBuilder.ToString();
}

[CollectionDataContract]
public class MyReadOnlyCollection<T> : ReadOnlyCollection<T>
{
    public MyReadOnlyCollection(IList<T> list) : base(list)
    {
    }
}

Two questions:

1. Why can I serialization ReadOnlyCollection but not my derived class?
2. How should I serialize my derived class correctly?

Update: I've added my derived class above

Answer 1

How should I serialize my derived class correctly? to serialize your derived class correctly you should do something like this

[DataContract]
public class MyReadOnlyCollection<T>:ReadOnlyCollection<T>
{

    public MyReadOnlyCollection(IList<T> list) : base(list)
    {
    }
}

EDIT

You cannot use [CollectionDataContract] because it does not fully meet collection type requirements as the Add method is missing so the type is not considered as a collection type

For more information Collection Types in Data Contracts