using Newtonsoft.Json;

using Newtonsoft.Json.Serialization;

using System;

using System.Globalization;

​

public class MyJsonConverter : JsonConverter

{

    public override bool CanConvert(Type objectType) => objectType == typeof(double) || objectType == typeof(double?);

​

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

    {

        if (value is double input && double.IsFinite(input))

            writer.WriteRawValue(input.ToString("G3", NumberFormatInfo.InvariantInfo));

        else

            writer.WriteNull();

    }

​

    public override object? ReadJson(JsonReader reader, Type objectType, object? existingValue, JsonSerializer serializer) => throw new NotImplementedException();

}

​

public class SkipNullPropertyContractResolver : DefaultContractResolver

{

    protected override JsonProperty CreateProperty(System.Reflection.MemberInfo member, MemberSerialization memberSerialization)

    {

        var property = base.CreateProperty(member, memberSerialization);

​

        // Override the ShouldSerialize method to check if the value is null after applying the converter

        property.ShouldSerialize = instance =>

        {

            var value = property.ValueProvider.GetValue(instance);

            if (value == null)

                return false;

​

            // Use a dummy JsonWriter to determine if the converter will output null

            using (var writer = new System.IO.StringWriter())

            {

                var jsonWriter = new JsonTextWriter(writer);

                var serializer = new JsonSerializer();

                serializer.Converters.Add(new MyJsonConverter());

​

                serializer.Serialize(jsonWriter, value);

                var serializedValue = writer.ToString();

​

                return serializedValue != "null";

            }

        };

​

        return property;

    }

}

​

public record A(

    double d,

    double? nd1,

    double? nd2,

    double? nd3,

    double[] da,

    double?[] nda)

{ }

​

class Program

{

    static void Main(string[] args)

    {

        var test = new A(

            d: 1.23456789,

            nd1: 1.23456789,

            nd2: null,

            nd3: double.NaN,

            da: new[] { 1.23456789 },

            nda: new double?[] { 1.23456789, null, double.NaN });

​

        var settings = new JsonSerializerSettings

        {

            NullValueHandling = NullValueHandling.Ignore,

            Converters = { new MyJsonConverter() },

            ContractResolver = new SkipNullPropertyContractResolver()

        };

​

        var json = JsonConvert.SerializeObject(test, settings);

        Console.WriteLine(json);

    }

}

​