using System;

using System.ComponentModel;

using System.Web;

using System.Reflection;

using System.Linq;

using System.Collections.Generic;

using System.Globalization;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var testString = "Number=6&Id=a355921d-a429-4952-b744-210b98a7fbe6&Values=a,b";

        var deserialized2 = FormUrlEncodedDeserializerV2.Deserialize<DataV2>(testString);

        Console.WriteLine("number: " + deserialized2.Number);

        Console.WriteLine("id: " + deserialized2.Id);

        Console.WriteLine("values: " + string.Join(", ", deserialized2.Values));

    }

    public class DataV2 {

        public int Number {get;}

        public Guid Id{get;}

        [JsonConverter(typeof(ListToCsvConverter))]

        public List<string> Values {get;}

        public DataV2(int number, Guid id, List<string> values) {

            Number = number;

            Id = id;

            Values = values;

        }

    }

    public static class FormUrlEncodedDeserializerV2 {

        public static T Deserialize<T>(string formUrlEncoded) 

        {

            var keyValues = HttpUtility.ParseQueryString(formUrlEncoded);

            var dictionary = keyValues.AllKeys.ToDictionary(k => k, k => keyValues[k]);

            var json = JsonConvert.SerializeObject(dictionary);

            return JsonConvert.DeserializeObject<T>(json);

        }

    }

    public class ListToCsvConverter : JsonConverter

    {

        public override bool CanConvert(Type objectType)

        {

            return objectType == typeof(List<string>);

        }

​

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

        {

            writer.WriteValue(string.Join(",", (List<string>)value));

        }

​

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

        {

            return new List<string>(((string)reader.Value).Split(','));

        }

    }

}