using System;

using System.Collections;

using System.Collections.Generic;

using System.Text.Json;

using System.Text.Json.Serialization;

using System.Linq;

public class Program

{

    public static void Main()

    {

        MyItems myItems1 = new MyItems([1, 2, 3]);

        JsonSerializerOptions options = new JsonSerializerOptions {  };

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

        string jsonStr = System.Text.Json.JsonSerializer.Serialize(myItems1); // produces string '[1,2,3]'

        MyItems? myItems2 = System.Text.Json.JsonSerializer.Deserialize<MyItems>(jsonStr, options); // throws

        Console.WriteLine(String.Join(',', myItems2));

    }

}

​

public class MyItemsConverter : JsonConverter<MyItems>

{

    public override MyItems Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)

    {

        if (reader.TokenType != JsonTokenType.StartArray)

        {

            throw new JsonException();

        }

​

        var obj = new MyItems(JsonSerializer.Deserialize<IReadOnlyCollection<int>>(ref reader, options));

​

        return obj;

     }

​

     public override void Write(Utf8JsonWriter writer, MyItems value, JsonSerializerOptions options)

     {

         JsonSerializer.Serialize(writer, value);

     }

}

​

public class MyItems : IReadOnlyCollection<int>

{

    private readonly List<int> _items;

​

    [JsonConstructor]

    public MyItems(IReadOnlyCollection<int> items)

    {

        _items = items != null ? new List<int>(items) : new List<int>();

    }

​

    [JsonIgnore]

    public int Count => _items.Count;

​

    public IEnumerator<int> GetEnumerator()

    {

        return _items.GetEnumerator();

    }

​

    IEnumerator IEnumerable.GetEnumerator()

    {

        return GetEnumerator();

    }

}