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 System.Text.Json;

using System.Text.Json.Serialization;

​

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

​

//https://stackoverflow.com/questions/67724103/how-to-serialize-arraylist-into-concrete-type-using-system-text-json

​

    public class Test

    {

        public int MyProperty { get; set; }            

        public ArrayList list { get; set; }

    }

    public class Employee

    {

        public int MyProperty { get; set; }

        public string Name { get; set; }

    }

​

    public class KnownItemTypeArrayListConverter<TItem> : JsonConverter<ArrayList>

    {

        public override ArrayList Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) =>

            new ArrayList(JsonSerializer.Deserialize<List<TItem>>(ref reader, options));

        public override void Write(Utf8JsonWriter writer, ArrayList value, JsonSerializerOptions options) =>

            JsonSerializer.Serialize(writer, value.Cast<TItem>(), options);

    }

​

    class TestClass

    {

        public static void Test()

        {

            var e1 = new Employee { MyProperty = 1, Name = "Yash", };

            var e2 = new Employee { MyProperty = 1, Name = "Yash", };

            var t = new Test { list = new ArrayList { e1, e2 }, };

            var options = new JsonSerializerOptions

            {

                Converters = { new KnownItemTypeArrayListConverter<Employee>() },

                WriteIndented = true,

            };

            var text = JsonSerializer.Serialize(t, options);

            var t2 = JsonSerializer.Deserialize<Test>(text, options);

​

            Console.WriteLine(JsonSerializer.Serialize(t2, options));

            Assert.IsTrue(t2.list.Cast<object>().All(i => i is Employee));

        }

    }

​

    public class Program

    {

        public static void Main()

        {

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

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

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

        public static string GetNetCoreVersion()

        {

            //https://techblog.dorogin.com/how-to-detect-net-core-version-in-runtime-ecd65ad695be

            //

            var assembly = typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly;

            var assemblyPath = assembly.Location.Split(new[] { '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);

            int netCoreAppIndex = Array.IndexOf(assemblyPath, "Microsoft.NETCore.App");

            if (netCoreAppIndex > 0 && netCoreAppIndex < assemblyPath.Length - 2)

                return assemblyPath[netCoreAppIndex + 1];

            return "";

        }

    }

​