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 System.Reflection;

using System.Collections.ObjectModel;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/73254871/can-i-set-my-own-default-listt-converter-in-json-net-without-attributes

​

#nullable enable

​

    public class ArrayObjectConverter : JsonConverter

    {

        public override bool CanConvert(Type t) => t.GetListItemType() != null;

        public override bool CanWrite => false;

        public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer) => throw new NotImplementedException();

​

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

        {

            System.Diagnostics.Debug.Assert(objectType.GetListItemType() != null);

            if (reader.MoveToContentAndAssert().TokenType == JsonToken.Null)

                return null;

            IList value = existingValue as IList ?? (IList)serializer.ContractResolver.ResolveContract(objectType).DefaultCreator!();

​

            if (reader.TokenType == JsonToken.StartArray)

            {

                serializer.Populate(reader, value);

            }

            else if (reader.TokenType == JsonToken.StartObject)

            {

                var itemType = objectType.GetListItemType().ThrowOnNull();

                while (reader.ReadToContentAndAssert().TokenType != JsonToken.EndObject)

                {

                    // Eat the property name

                    reader.AssertTokenType(JsonToken.PropertyName).ReadToContentAndAssert();

                    // Deserialize the property value and add it to the list.

                    value.Add(serializer.Deserialize(reader, itemType));

                }

            }

            else

            {

                throw new JsonSerializationException(string.Format("Unknown token type {0}", reader.TokenType));

            }

            return value;

        }

    }

​

    public static partial class JsonExtensions

    {

        public static JsonReader AssertTokenType(this JsonReader reader, JsonToken tokenType) => 

            reader.TokenType == tokenType ? reader : throw new JsonSerializationException(string.Format("Unexpected token {0}, expected {1}", reader.TokenType, tokenType));

        public static JsonReader ReadToContentAndAssert(this JsonReader reader) =>

            reader.ReadAndAssert().MoveToContentAndAssert();

​

        public static JsonReader MoveToContentAndAssert(this JsonReader reader)

        {

            if (reader == null)

                throw new ArgumentNullException();

            if (reader.TokenType == JsonToken.None)       // Skip past beginning of stream.

                reader.ReadAndAssert();

            while (reader.TokenType == JsonToken.Comment) // Skip past comments.

                reader.ReadAndAssert();

            return reader;

        }

​

        public static JsonReader ReadAndAssert(this JsonReader reader)

        {

            if (reader == null)

                throw new ArgumentNullException();

            if (!reader.Read())

                throw new JsonReaderException("Unexpected end of JSON stream.");

            return reader;

        }

        public static Type? GetListItemType(this Type type)

        {

            // Quick reject for performance

            if (type.IsPrimitive || type.IsArray || type == typeof(string))

                return null;

            while (type != null)

            {

                if (type.IsGenericType)

                {

                    var genType = type.GetGenericTypeDefinition();

                    if (genType == typeof(List<>))

                        return type.GetGenericArguments()[0];

                }

                type = type.BaseType!;

            }

            return null;

        }

    }

​

    public static partial class ObjectExtensions

    {

        public static T ThrowOnNull<T>(this T? value) where T : class => value ?? throw new ArgumentNullException(nameof(value));

    }

​

    public class Model<T>

    {

        public List<T> SomeArr { get; set; } = new ();

    }

​

    public class Item

    {

        public string? prop1 { get; set; }

    }

​

    class TestClass

    {

        public static void Test()

        {

            TestObjectList();

            TestPrimitiveList();

        }

​

        static void TestPrimitiveList()

        {

            foreach (var json in GetPrimitiveJson())

            {

                var settings = new JsonSerializerSettings

                {

                    Converters = { new ArrayObjectConverter() },

                };

                var model = JsonConvert.DeserializeObject<Model<string>>(json, settings);

                Console.WriteLine(JsonConvert.SerializeObject(model, settings));

​

                Assert.AreEqual(4, model?.SomeArr?.Count);

            }

        }

        static void TestObjectList()

        {

            foreach (var json in GetObjectJson())

            {

                var settings = new JsonSerializerSettings

                {

                    Converters = { new ArrayObjectConverter() },

                };

                var model = JsonConvert.DeserializeObject<Model<Item>>(json, settings);

                Console.WriteLine(JsonConvert.SerializeObject(model, settings));

                Assert.AreEqual(2, model?.SomeArr?.Count);

            }

        }   

        static IEnumerable<string> GetObjectJson() => new []

        {

@"{""SomeArr"" : /* Comment */ [  /* Comment */ { ""prop1"":""value1"" }, { ""prop1"":""value1"" }]}",

@"{""SomeArr"":

{

    /* Comment */ ""item1"":  /* Comment */{  /* Comment */""prop1"":""value1"" },

    ""item2"": {  /* Comment */""prop1"":""value1"" /* Comment */ }

}}"

        };

        static IEnumerable<string> GetPrimitiveJson() => new []

        {

@"{""SomeArr"": /* Comment */ [""a"", ""b"", null, ""c""]}",

@"{""SomeArr"":

{

    /* Comment */ ""item1"": ""a"",  /* Comment */

    /* Comment */ ""item2"": ""b"",

    /* Comment */ ""item3"": null,

    /* Comment */ ""item4"": ""c"",

}}"

        };

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version);

            Console.WriteLine("{0} version: {1}", typeof(JsonSerializer).Assembly.GetName().Name,  typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​