需要新增引用：

System.Runtime.Serialization;

System.ServiceModel.Web

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Json;

namespace JsonToObjects
{
    public class ObjectToJsons
    {
        // 從一個物件資訊生成Json串
        public static string ObjectToJson(object obj)
        {
           DataContractJsonSerializer serializer = new DataContractJsonSerializer(obj.GetType());
           MemoryStream stream = new MemoryStream();
           serializer.WriteObject(stream, obj);
           byte[] dataBytes = new byte[stream.Length];
           stream.Position = 0;
           stream.Read(dataBytes, 0, (int)stream.Length);
           return Encoding.UTF8.GetString(dataBytes);
        }
        // 從一個Json串生成物件資訊
        public static object JsonToObject(string jsonString, object obj)
        {
           DataContractJsonSerializer serializer = new DataContractJsonSerializer(obj.GetType());
           MemoryStream mStream = new MemoryStream(Encoding.UTF8.GetBytes(jsonString));
           return serializer.ReadObject(mStream);
        }
    }
}