using System;

    using System.Collections.Generic;

​

    using Newtonsoft.Json;

    using Newtonsoft.Json.Linq;

    using Newtonsoft.Json.Serialization;    

​

    public class Program    

    {

        public class Foo

        {

            public int Id { get; set; }

​

            //[JsonExtensionData]

            public IDictionary<string, object> ExtensionData { get; set; } 

        }

​

        public class FooContractResolver : DefaultContractResolver

        {

            protected override JsonObjectContract CreateObjectContract(Type objectType)

            {

                var contract = base.CreateObjectContract(objectType);

                if (objectType == typeof(Foo))

                {

                    contract.ExtensionDataGetter =

                    (o) =>

                    {

                        var result = new List<KeyValuePair<object, object>>();

​

                        foreach(KeyValuePair<string, object> obj in (o as Foo).ExtensionData)

                        {

                            result.Add(new KeyValuePair<object, object>(obj.Value, obj.Key));

                        }

​

                        return result;

                    };

                }

​

                return contract;

            }

        }

​

        public static void Main()

        {

            Foo foo = new Foo();

            foo.ExtensionData = new Dictionary<string, object>();

            foo.ExtensionData.Add("Name", default(int));

            Console.WriteLine(JsonConvert.SerializeObject((foo), new JsonSerializerSettings() { 

                ContractResolver = new FooContractResolver()

            }));

        }

    }