using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.IO;

using System.Data;

using System.Globalization;

​

using System.Xml;

using System.Xml.Serialization;

using System.Xml.Linq;

​

using System.Text.Json;

​

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

​

//https://stackoverflow.com/questions/76137206/c-sharp-how-to-xml-deserialize-a-dictionarystring-liststing

​

    using System.Runtime.Serialization;

​

    [DataContract(Name = "CountriesAndCities", Namespace = "https://stackoverflow.com/q/76137206")] // Use your preferred namespace URI here.  Could be empty.

    public class CountriesAndCities

    {

        [DataMember]

        public Dictionary<string, List<string>> DictCountriesAndCities { get; set; } = new ();

    };

​

    class TestClass

    {

        public static void Test()

        {

            CountriesAndCities container = new()

            {

                DictCountriesAndCities = 

                {

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

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

                }

            };

            var fileName = "Question76137206.xml";

            using (var writer = XmlWriter.Create(fileName, new XmlWriterSettings {Indent = true} )) 

            {

                (new DataContractSerializer(container.GetType())).WriteObject(writer, container);

            }

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

            CountriesAndCities container2;

            using (var reader = XmlReader.Create(fileName)) 

            {

                container2 = (CountriesAndCities)(new DataContractSerializer(container.GetType())).ReadObject(reader);

            }

​

            Assert.That(container.DictCountriesAndCities.Count == container2.DictCountriesAndCities.Count);

            var json1 = JsonSerializer.Serialize(container, new JsonSerializerOptions { WriteIndented = true });

            var json2 = JsonSerializer.Serialize(container2, new JsonSerializerOptions { WriteIndented = true });

            Assert.AreEqual(json1, json2);

            using (var stream = File.Create(fileName))

            {

                JsonSerializer.Serialize(stream, container, new JsonSerializerOptions { WriteIndented = true });

            }

            CountriesAndCities container3;

            using (var stream = File.OpenRead(fileName))

            {

                container3 = JsonSerializer.Deserialize<CountriesAndCities>(stream);

            }

            var json3 = JsonSerializer.Serialize(container2, new JsonSerializerOptions { WriteIndented = true });

            Assert.AreEqual(json1, json3);

            Console.WriteLine("\nJSON generated by JsonSerializer:");

            Console.WriteLine(json3);

        }   

    }

​

    public static partial class DataContractSerializerHelper

    {

        public static string ToContractXml<T>(this T obj, DataContractSerializer serializer = null, XmlWriterSettings settings = null)

        {

            serializer = serializer ?? new DataContractSerializer(obj == null ? typeof(T) : obj.GetType());

            using (var textWriter = new StringWriter())

            {

                settings = settings ?? new XmlWriterSettings { Indent = true };

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

                {

                    serializer.WriteObject(xmlWriter, obj);

                }

                return textWriter.ToString();

            }

        }

​

        public static T FromContractXml<T>(string xml, DataContractSerializer serializer = null)

        {

            using (var textReader = new StringReader(xml ?? ""))

            using (var xmlReader = XmlReader.Create(textReader))

            {

                return (T)(serializer ?? new DataContractSerializer(typeof(T))).ReadObject(xmlReader);

            }

        }

    }

​

    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;

            }

        }

    }

​