How do I serialize ObservableCollection-derived class to and from JSON?

Question

For .NET. I've tried a lot of different things, but nothing seems to work. Requirements:

1. The T of ObservableCollection<T> is an ISerializable
2. The ObservableCollection-derived-class ideally is also an ISerializable
3. For this context, being an ISerializable = uses only ISerializable technique for serialization, not reflected properties

Environment is Xamarin for Android, I'd prefer to use either JSON.NET or DataContractJsonSerializer. Example uses Newtonsoft 9.0.1

With code like this:

[Serializable]
[KnownType(typeof(ObservableCollectionSerializable.Item))]
public class ObservableCollectionSerializable : 
    ObservableCollection<ObservableCollectionSerializable.Item>
{
    [Serializable]
    public class Item : ISerializable
    {
        readonly string value;

        public Item(string value) { this.value = value; }

        public Item(SerializationInfo info, StreamingContext context)
        {
            value = info.GetString("value");
        }

        public void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            info.AddValue("value", value);
        }
    }
}

Invoked like this:

            var _item = new Test.ObservableCollectionSerializable.Item("test1");
            var c = new Test.ObservableCollectionSerializable();

            c.Add(_item);

            var serializer = new Newtonsoft.Json.JsonSerializer();
            serializer.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver()
            {
                //IgnoreSerializableInterface = false // not available
            };
            var stringWriter = new StringWriter();

            serializer.Serialize(stringWriter, c);

            var json = stringWriter.ToString();                

            var stringReader = new StringReader(json);

            var c2 = (Test.ObservableCollectionSerializable)
                serializer.Deserialize(stringReader, typeof(Test.ObservableCollectionSerializable));

            var item = c2[0];

Results are:

• "json" variable always ends up "[{}]" - empty
• ISerialize-based methods are never called
• serializer.Deserialize call always throws exception "Newtonsoft.Json.JsonSerializationException: Unable to find a constructor to use for type Notos.App.UI.Android.Test.ObservableCollectionSerializable+Item. A class should either have a default constructor, one constructor with arguments or a constructor marked with the JsonConstructor attribute. Path '[0]', line 1, position 3"