using System;
using System.IO;
using System.Xml.Serialization;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            //string directory = Path.Combine(
            //    Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "ProgramName");
            string directory = Path.Combine("D:\", "ProgramName");
            string file = Path.Combine(directory, "data.xml");

            Data data = new Data
            {
                Amount = 150m
            };

            Display(data, "Исходный вариант");
            try
            {
                if (!Directory.Exists(directory))
                {
                    Directory.CreateDirectory(directory);
                }
                Serializer.SaveToXml(file, data);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }

            // Как будто читаем где-то в другом месте программы и не сразу же после записи
            // -----------------------------
            try
            {
                Data fromFile = null;
                if (File.Exists(file))
                {
                    fromFile = Serializer.LoadXml<Data>(file);
                }
                else
                {
                    fromFile = new Data();
                }

                Display(fromFile, "Прочитанный из файла");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }

            Console.ReadKey();
        }

        private static void Display(Data data, string message)
        {
            Console.WriteLine(message + ". Amount: {0}", data.Amount);
        }
    }

    public class Data
    {
        public decimal Amount { get; set; }
    }

    public static class Serializer
    {
        public static void SaveToXml<T>(String fileName, T serializableObject)
        {
            XmlSerializer serializer = new XmlSerializer(typeof(T));
            using (TextWriter textWriter = new StreamWriter(fileName))
            {
                serializer.Serialize(textWriter, serializableObject);
            }
        }

        public static T LoadXml<T>(String fileName)
        {
            XmlSerializer serializer = new XmlSerializer(typeof(T));
            using (TextReader textReader = new StreamReader(fileName))
            {
                return (T)serializer.Deserialize(textReader);
            }
        }
    }
}