using System;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var foo = new Foo{ X = 0 };

        var foo2 = new Foo2{ X = 0 };

        var bar = new Bar { X = 0 };

        Console.WriteLine(JsonConvert.SerializeObject(foo));

        Console.WriteLine(JsonConvert.SerializeObject(foo2));

        Console.WriteLine(JsonConvert.SerializeObject(bar));

    }

}

public class Foo

{

    [JsonConverter(typeof(ZeroToNullConverter))]

    public int? X { get; set; }

}

// 単純に継承しただけでは JsonConverter 属性も引き継がれる

public class Foo2 : Foo

{

}

// JsonConverter を剥がす

public class Bar : Foo

{

    new public int? X { get; set; }

}

​

public class ZeroToNullConverter : JsonConverter

    {

        public override bool CanConvert(Type objectType)

        {

            return objectType == typeof(int?);

        }

​

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

        {

            int? number = (int?)value;

            if (number != 0)

            {

                writer.WriteValue(number);

            }

            else

            {

                writer.WriteNull();

            }

        }

​

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

        {

            //CanReadがfalseのため、ReadJsonは呼び出されない

            throw new NotImplementedException();

        }

        //ReadJsonの呼び出しをスキップする

        public override bool CanRead

        {

            get { return false; }

        }

    }