CheckedEnumJsonConverter.cs

using System;
using Newtonsoft.Json;
using Newtonsoft.Json.Converters;

namespace X
{
    public class CheckedStringEnumConverter : StringEnumConverter
    {
        public CheckedStringEnumConverter() : this (false)
        {
        }

        public CheckedStringEnumConverter(bool serializeAsNumbers)
        {
            SerializeAsNumbers = serializeAsNumbers;
        }

        public bool SerializeAsNumbers { get; }

        public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer)
        {
            if (SerializeAsNumbers && value != null)
            {
                var underlyingValue = Convert.ChangeType(value, value.GetType().GetEnumUnderlyingType());
                writer.WriteValue(underlyingValue);
            }
            else
            {
                base.WriteJson(writer, value, serializer);
            }
        }

        public override object? ReadJson(JsonReader reader, Type objectType, object? existingValue, JsonSerializer serializer)
        {
            var value = base.ReadJson(reader, objectType, existingValue, serializer);
            if (value is null)
            {
                return null;
            }
            var underlyingValue = Convert.ChangeType(value, objectType.GetEnumUnderlyingType());
            if (!Enum.IsDefined(objectType, underlyingValue))
            {
                throw new JsonSerializationException($"{underlyingValue} is not valid value of type {objectType.Name}");
            }

            return value;
        }
    }
}