using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

​

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/78353143/custom-jsonconverter-for-seserializing-json-to-abstract-class

​

public class Root // Not shown in your question

{

    public List<Event> events { get; set; } = new();

}

​

public class Event

{

    public int id { get; set; } // Does this have a fixed value of 1?

    public List<ActionHolder> actions { get; set; } = new();

}

​

[JsonConverter(typeof(ActionHolderConverter))]

public class ActionHolder

{

    public int id => (int)(values?.id ?? ActionValueType.None);

    public ActionValueBase values { get; set; }

}

​

public enum ActionValueType

{

    None = -1,

    OpenURL = 8,

    Scale = 15,

}

​

public abstract class ActionValueBase

{

    [JsonIgnore] public abstract ActionValueType id { get; }

    public int obj_id { get; set; }

}

​

public class OpenURLActionValue : ActionValueBase

{

    public override ActionValueType id => ActionValueType.OpenURL;

    public string url { get; set; }

}

​

public class ScaleActionValue : ActionValueBase

{

    public override ActionValueType id => ActionValueType.Scale;

    public float scale { get; set; } = 1;

}

​

class ActionHolderConverter : JsonConverter<ActionHolder>

{

    public override ActionHolder ReadJson(JsonReader reader, Type objectType, ActionHolder existingValue, bool hasExistingValue, JsonSerializer serializer)

    {

        JObject joAction = JObject.Load(reader);

        var values = (ActionValueType)joAction[nameof(ActionHolder.id)].Value<int>() switch

        {

            ActionValueType.Scale => joAction[nameof(ActionHolder.values)]?.ToObject<ScaleActionValue>(serializer),

            ActionValueType.OpenURL => joAction[nameof(ActionHolder.values)]?.ToObject<OpenURLActionValue>(serializer),

            ActionValueType.None => (ActionValueBase)null,

            var t => throw new JsonSerializationException($"Unknown ActionValueTypes {t}"),

        };

        var holder = existingValue ?? new ActionHolder();

        holder.values = values;

        return holder;

    }

​

    public override bool CanWrite => false;

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

}

​

    class TestClass

    {

        public static void Test()

        {

            var json = GetJson();

            var settings = new JsonSerializerSettings

            {

                ContractResolver = new CamelCasePropertyNamesContractResolver(),

            };

​

            var root = JsonConvert.DeserializeObject<Root>(json, settings);

            //root.Dump();

            var json2 = JsonConvert.SerializeObject(root, Formatting.Indented, settings);

            Console.WriteLine("Re-serialized {0}:", root);

            Console.WriteLine(json2);

            Assert.That(JToken.DeepEquals(JToken.Parse(json), JToken.Parse(json2)));

        }   

        static string GetJson() =>

            """

            {

               "events":[

                  {

                     "id":1,

                     "actions":[

                        {

                           "id":8,

                           "values":{

                              "obj_id":160,

                              "url":"https://www.myurl.com/"

                           }

                        },

                        {

                           "id":15,

                           "values":{

                              "obj_id":182,

                              "scale":200.0

                           }

                        }

                     ]

                  }

               ]

            }

            """;

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1}), {2}", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion);

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

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​