using System;

using System.Collections.Generic;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var invoice = new test {

            InvoiceDetail = new List<IInvoiceDetail>

            {

                new InvoiceDetail { Item = "a", Price = 1, },

                new InvoiceDetail { Item = "b", Price = 2, },

            },

            VatDetail = new List<IVatDetail>

            {

                new VatDetail { Rate = 0.10M, Amount = 1, },

                new VatDetail { Rate = 0.20M, Amount = 2, },

            },

        };

        var json = JsonConvert.SerializeObject(invoice, Formatting.Indented);

        Console.WriteLine(json);

        var newInvoice = JsonConvert.DeserializeObject<test>(json);

        Console.WriteLine(JsonConvert.SerializeObject(newInvoice, Formatting.Indented));

    }

}

​

public class InvoiceDetailConverter<TConcrete, TInterface> : JsonConverter where TConcrete : TInterface

{

    public override bool CanConvert(Type objectType)

    {

        //assume we can convert to anything for now

        return true;

    }

​

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)

    {

        List<TConcrete> data = serializer.Deserialize<List<TConcrete>>(reader);

​

        // now loop to make the proper list

        List<TInterface> result = new List<TInterface>();

        foreach (TInterface d in data)

        {

            result.Add(d);

        }

        return result;

    }

​

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

    {

        //use the default serialization - it works fine

        serializer.Serialize(writer, value);

    }

}

​

public interface IInvoiceDetail

{

    string Item { get; set; }

    int Price { get; set; }

}

​

public class InvoiceDetail : IInvoiceDetail

{

    public string Item { get; set; }

    public int Price { get; set; }

}

​

public interface IVatDetail

{

    decimal Rate { get; set; }

    int Amount { get; set; }

}

​

public class VatDetail : IVatDetail

{

    public decimal Rate { get; set; }

    public int Amount { get; set; }

}

​

public class test

{

    [JsonConverter(typeof(InvoiceDetailConverter<InvoiceDetail, IInvoiceDetail>))]

    public List<IInvoiceDetail> InvoiceDetail { get; set; }

    [JsonConverter(typeof(InvoiceDetailConverter<VatDetail, IVatDetail>))]

    public List<IVatDetail> VatDetail { get; set; }

}

​