using System;

using Newtonsoft.Json;

using System.Collections.Generic;

using System.Text.Json;

using System.Text.Json.Serialization;

public class IntListConverter : System.Text.Json.Serialization.JsonConverter<List<int>>

{

    public override List<int> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)

    {

        if (reader.TokenType == JsonTokenType.StartArray)

        {

            List<int> numbers = new List<int>();

            while (reader.Read())

            {

                if (reader.TokenType == JsonTokenType.EndArray)

                {

                    return numbers;

                }

                var sValue = reader.GetString();

                if (Int32.TryParse(sValue,out int value))

                    {

                        numbers.Add(value);

                    }

            }

        }

        throw new System.Text.Json.JsonException("Invalid JSON format.");

    }

​

    public override void Write(Utf8JsonWriter writer, List<int> value, JsonSerializerOptions options)

    {

        writer.WriteStartArray();

        foreach (int number in value)

        {

            writer.WriteNumberValue(number);

        }

        writer.WriteEndArray();

    }

}

​

public class Program

{

    public static void Main()

    {

        var asd =  Newtonsoft.Json.JsonConvert.DeserializeObject< List<int> >("[\"1\",\"3\",\"2\"]");

        Console.WriteLine(string.Join(",",asd));

        JsonSerializerOptions options = new JsonSerializerOptions();

        options.Converters.Add(new IntListConverter());

        var asd2 = System.Text.Json.JsonSerializer.Deserialize<List<int>>("[\"1\",\"3\",\"2\"]",options);

        Console.WriteLine(string.Join(",",asd2));

    }

}

​

​