using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/54055420/json-deserialization-returns-null/54055463#54055463

    public class CategoryVM

    {

        public Category category { get; set; }

        public CategoryImage categoryImage { get; set; }

​

        public CategoryVM()

        {

            category = new Category(); 

            categoryImage = new CategoryImage(); 

        }

    }

​

    public class Category

    {

        public string Kategori { get; set; }

        public string Kodu { get; set; }

        public bool State { get; set; }

    }

​

    public class CategoryImage

    {

        // Left unmdefined since not included in the question.

    }

​

    class TestClass

    {

        public static void Test()

        {

            var cat = GetJson();

            var c = JsonConvert.DeserializeAnonymousType(cat, new { cat = default(CategoryVM) })

                .cat.category;

            Console.WriteLine("Deserialized {0}:", c);

            Console.WriteLine(JsonConvert.SerializeObject(c, Formatting.Indented));

​

            // Assert we got the correct Category values

            Assert.IsTrue(c.Kategori == JToken.Parse(cat).SelectToken("..Kategori").ToString());

            Assert.IsTrue(c.Kodu == JToken.Parse(cat).SelectToken("..Kodu").ToString());

            Assert.IsTrue(c.State == (bool)JToken.Parse(cat).SelectToken("..State"));

        }   

        static string GetJson()

        {

            var json = @"{

    ""cat"": {

        ""Category"": {

            ""Kategori"": ""xxx"",

            ""Kodu"": ""yyy"",

            ""State"": ""true""

        }

    }

}

";

            return json;

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: " + Environment.Version);

            Console.WriteLine("Json.NET version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​