using System;

using System.Collections.Generic;

using System.Text;

using System.Linq;

using System.Xml.Serialization;

using System.Xml;

using System.Xml.Linq;

using System.IO;

using System.Data;

​

using System.Text.Json;

​

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

​

//https://stackoverflow.com/questions/73127531/how-to-add-a-new-node-to-an-existing-xml-using-c-sharp

​

    [XmlRoot("CountriesAndCities")]

    public class CountriesAndCities

    {

        public Country [] Name      // Replace the List<Country> with Country []

        {

            get { return DictCountriesAndCities.Select(x => new Country { CountryName = x.Key, Cities = x.Value }).ToArray(); }

            set { DictCountriesAndCities = value?.ToDictionary(x => x.CountryName, x => x.Cities); }

        }

        [XmlIgnore]

        public Dictionary<string, List<string>> DictCountriesAndCities { get; set; }

    }

​

    public class Country

    {

        public string CountryName { get; set; }

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

    }

​

    public class TestClass

    {

        public static void Test()

        {

            Dictionary<string, List<string>> dictCountriesAndCities = new ()

            {

                ["entry1"] = new() { "a", "b", "c" },

                ["entry2"] = new() { "a", "b", "c" },

            };

            var fileName = "Question76137206.xml";

​

            TestWrite(dictCountriesAndCities, fileName);

            Console.WriteLine(File.ReadAllText(fileName));

​

            var dict2 = TestRead(fileName);

            Assert.AreEqual(dictCountriesAndCities.Count, dict2.Count);

            Assert.AreEqual(JsonSerializer.Serialize(dictCountriesAndCities), JsonSerializer.Serialize(dict2));

        }

        static void TestWrite(Dictionary<string, List<string>> dictCountriesAndCities, string fileName)

        {

            var sfd = new  { FileName = fileName, };

​

            var container = new CountriesAndCities

            {

                DictCountriesAndCities = dictCountriesAndCities,

            };

            using (var writer = XmlWriter.Create(sfd.FileName, new XmlWriterSettings { Indent = true })) // Indentation is for visualization purposes only

                (new XmlSerializer(typeof(CountriesAndCities))).Serialize(writer, container);

        }

​

        static Dictionary<string, List<string>> TestRead(string fileName)

        {

            Dictionary<string, List<string>> dictCountriesAndCities;

            var ofd = new  { FileName = fileName, };

            using (var reader = new StreamReader(ofd.FileName))

            {

                dictCountriesAndCities = ((new XmlSerializer(typeof(CountriesAndCities))).Deserialize(reader) as CountriesAndCities)

                    ?.DictCountriesAndCities;

            }

            return dictCountriesAndCities;

        }

    }

​

    public static class XmlSerializationHelper

    {

        public static T LoadFromXml<T>(this string xmlString, XmlSerializer serial = null)

        {

            serial = serial ?? new XmlSerializer(typeof(T));

            using (var reader = new StringReader(xmlString))

            {

                return (T)serial.Deserialize(reader);

            }

        }

​

        public static string GetXml<T>(this T obj, bool omitStandardNamespaces)

        {

            return obj.GetXml(null, omitStandardNamespaces);

        }

        public static string GetXml<T>(this T obj, XmlSerializer serializer = null, bool omitStandardNamespaces = false)

        {

            XmlSerializerNamespaces ns = null;

            if (omitStandardNamespaces)

            {

                ns = new XmlSerializerNamespaces();

                ns.Add("", ""); // Disable the xmlns:xsi and xmlns:xsd lines.

            }           

            using (var textWriter = new StringWriter())

            {

                var settings = new XmlWriterSettings() { Indent = true }; // For cosmetic purposes.

                using (var xmlWriter = XmlWriter.Create(textWriter, settings))

                    (serializer ?? new XmlSerializer(obj.GetType())).Serialize(xmlWriter, obj, ns);

                return textWriter.ToString();

            }

        }

    }

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1}, {2})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​