using System;

using System.Linq;

using System.Reflection;

using System.Collections.Generic;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

​

public class Program

{

    public static void Main()

    {

        List<Base> x = new List<Base>()

        {

            new Child1() { Hey = "hey" },

            new Child2() { Ho = 1 }

        };

        JsonSerializerSettings settings = new JsonSerializerSettings();

        settings.Converters.Add(new CustomConverter());

        string result = JsonConvert.SerializeObject(x, settings);

        Console.WriteLine(result);

    }

}

​

public class CustomConverter : JsonConverter

{

    public override bool CanConvert(Type objectType)

    {

        return objectType.IsAssignableTo(typeof(Base));

    }

​

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

    {

        JToken t = JToken.FromObject(value);

​

        if (t.Type != JTokenType.Object)

        {

            t.WriteTo(writer);

        }

        else

        {

            JObject o = (JObject)t;

            IList<string> propertyNames = o.Properties().Select(p => p.Name).ToList();

​

            ServerJsonTypeAttribute attribute = (ServerJsonTypeAttribute) value.GetType().GetCustomAttribute(typeof(ServerJsonTypeAttribute));

​

            o.AddFirst(new JProperty("Type", attribute.Key));

​

            o.WriteTo(writer);

        }

    }

​

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

    {

        //TODO

        throw new NotImplementedException("");

    }

}

​

public abstract class Base { }

​

[ServerJsonTypeAttribute("Child1")]

public class Child1 : Base

{

    public string Hey { get; set; }

}

​

[ServerJsonTypeAttribute("Child2")]

public class Child2 : Base

{

    public int Ho { get; set; }

}

​

public class ServerJsonTypeAttribute : Attribute

{

    public ServerJsonTypeAttribute(string key) { Key = key; }

​

    public string Key { get; }

}