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/54207670/newtonsoft-populateobject-value-cannot-be-null-exception#54207670

​

public enum ErrorDisplayType : int 

{

    PopUp = 0,

    ErrorPane = 1,

    Statusbar = 2

}

​

[Serializable()]

public class ErrorObj 

{

   private string errorCode;

   private ErrorDisplayType errorDispType;

​

   public string ErrorCode 

   {

     get { return this.errorCode; }

     set {

        this.errorCode = value;

        if (errorCode != null)

        {

           this.setFields(errorCode);

        }

     }

   }

   public ErrorDisplayType ErrorDispType 

   {

      get { return this.errorDispType; }

      set { this.errorDispType = value; }

   }

​

    private void setFields(string errorCode) 

    {

       //this.errorDispType = (ErrorDisplayType)int.Parse(errorCode);

    }   

}

​

​

[Serializable]

public class ErrorDTO : IEnumerator, IEnumerable 

{

   private int indx = -1;

   private List<ErrorObj> errorList;

   public List<ErrorObj> ErrorList 

   {

     get { return this.errorList; }

     set { this.errorList = value; }

   }

   public ErrorDTO()

        {

            this.errorList = new List<ErrorObj>();

        }

   public bool MoveNext()

   {

      if (indx < errorList.Count - 1)      

      {                                    

         ++indx;                          

         return true;                     

      }                                    

      else                                 

      {                                    

         indx = -1;                       

         return false;                    

      }                                    

    }

    public void Reset()

    {

      this.indx = -1;

    }

    public object Current                                                            

    {                                                                               

       get                                                                          

       {                                                                            

         if (errorList.Count == 0 || indx < 0 || indx > errorList.Count - 1)

         { 

            return null;                                                         

         }

         return this.errorList[indx];                                             

       }                                                                            

    } 

    public IEnumerator GetEnumerator()  

    {

      return (IEnumerator)this;

    }

    public int Add(ErrorObj error)

    {

      this.errorList.Add(error);

      return 0;  

     } 

}

​

    class TestClass

    {

        public static void Test()

        {

            string json = TestClass.GetJson();

            Console.WriteLine(json);

            ErrorDTO resultDTO = new ErrorDTO();

            Newtonsoft.Json.JsonConvert.PopulateObject(json, resultDTO.ErrorList);

            Console.WriteLine("\nPopulated {0}", resultDTO);

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

        }   

        public static string GetJson()

        {

            ErrorDTO errDTO = new ErrorDTO();

            ErrorObj errObj = new ErrorObj();

            errObj.ErrorCode = "ABCD125";

            errObj.ErrorDispType = (ErrorDisplayType)int.Parse("1");

            errDTO.Add(errObj);

            string json = Newtonsoft.Json.JsonConvert.SerializeObject(errDTO);

            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;

            }

        }

    }

​