using System;

using System.Collections.Generic;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main(string[] args)

    {

        string json = @"

        [

          {

            ""email"": ""john.doe@sendgrid.com"",

            ""timestamp"": 1337966815,

            ""category"": [

              ""newuser"",

              ""transactional""

            ],

            ""event"": ""open""

          },

          {

            ""email"": ""jane.doe@sendgrid.com"",

            ""timestamp"": 1337966815,

            ""category"": ""olduser"",

            ""event"": ""open""

          }

        ]";

​

        List<Item> list = JsonConvert.DeserializeObject<List<Item>>(json);

​

        foreach (Item obj in list)

        {

            Console.WriteLine("email: " + obj.Email);

            Console.WriteLine("timestamp: " + obj.Timestamp);

            Console.WriteLine("event: " + obj.Event);

            Console.WriteLine("categories: " + string.Join(", ", obj.Categories));

            Console.WriteLine();

        }

        json = JsonConvert.SerializeObject(list, Formatting.Indented);

        Console.WriteLine(json);

    }

}

​

class Item

{

    [JsonProperty("email")]

    public string Email { get; set; }

​

    [JsonProperty("timestamp")]

    public int Timestamp { get; set; }

​

    [JsonProperty("event")]

    public string Event { get; set; }

​

    [JsonProperty("category")]

    [JsonConverter(typeof(SingleOrArrayConverter<string>))]

    public List<string> Categories { get; set; }

}

​

class SingleOrArrayConverter<T> : JsonConverter

{

    public override bool CanConvert(Type objectType)

    {

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

    }

​

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

    {

        JToken token = JToken.Load(reader);

        if (token.Type == JTokenType.Array)

        {

            return token.ToObject<List<T>>();

        }

        return new List<T> { token.ToObject<T>() };

    }

​

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

    {

        List<T> list = (List<T>)value;

        if (list.Count == 1)

        {

            value = list[0];

        }

        serializer.Serialize(writer, value);

    }

}