using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

​

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

// https://stackoverflow.com/questions/49758659/how-to-construct-object-programmatically-inside-of-jsonconverter-writeobject

​

    public class SubObject

    {

        public string Foo { get; set; }

    }

​

    public class RootObject

    {

        public SubObject PropertyA { get; set; }

    }

​

    public class TestConverter1 : JsonConverter

    {

        public override bool CanConvert(Type objectType)

        {

            return objectType == typeof(RootObject);

        }

​

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

        {

            throw new NotImplementedException();

        }

​

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

        {

            //Console.WriteLine(GetType().Name + " called.");

            var e = (RootObject)value;

            writer.WriteStartObject();

            var fi = e.PropertyA;

            JObject o = JObject.FromObject(fi);

            o.AddFirst(new JProperty("type", new JValue(fi.GetType().Name)));

            writer.WritePropertyName("PropertyA");

            o.WriteTo(writer);

            writer.WriteEndObject();

        }

    }

​

    public class TestConverter2 : JsonConverter

    {

        public override bool CanConvert(Type objectType)

        {

            return objectType == typeof(RootObject);

        }

​

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

        {

            throw new NotImplementedException();

        }

​

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

        {

            //Console.WriteLine(GetType().Name + " called.");

            var e = (RootObject)value;

            var container = new JObject();

            var fi = e.PropertyA;

            JObject o = JObject.FromObject(fi);

            o.AddFirst(new JProperty("type", new JValue(fi.GetType().Name)));

            container.Add(new JProperty("PropertyA", o));

            container.WriteTo(writer);

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            var e = new RootObject { PropertyA = new SubObject { Foo = "foo" } };

​

            var settings1 = new JsonSerializerSettings

            {

                Converters = { new TestConverter1() },

            };

            var json1 = JsonConvert.SerializeObject(e, Formatting.Indented, settings1);

            Console.WriteLine("Serializing {0} with direct writing:", e);

            Console.WriteLine(json1);

            var settings2 = new JsonSerializerSettings

            {

                Converters = { new TestConverter2() },

            };

            var json2 = JsonConvert.SerializeObject(e, Formatting.Indented, settings2);

            Console.WriteLine("Serializing {0} via JObject:", e);

            Console.WriteLine(json1);           

        }

    }

​

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: " + Environment.Version);

            Console.WriteLine("Json.NET version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​

    public class AssertionFailedException : System.Exception

    {

        public AssertionFailedException() : base() { }

​

        public AssertionFailedException(string s) : base(s) { }

    }

​

    public static class Assert

    {

        public static void IsTrue(bool value)

        {

            IsTrue(value, "failed");

        }

​

        public static void IsTrue(bool value, string message)

        {

            if (value == false)

                throw new AssertionFailedException(message ?? "failed");

        }

    }

​