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.Runtime.Serialization;

​

using System.Text.Json;

​

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

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//https://stackoverflow.com/questions/75912029/easiest-way-to-serialize-an-iparsablet-as-a-string-using-the-datacontract-mode

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#nullable enable

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    public class MyType : IParsable<MyType>

    {

        public MyType(string? value1, string? value2) => (this.Value1, this.Value2) = (value1, value2);

        public string? Value1 { get; }

        public string? Value2 { get; }

        public override string ToString() => JsonSerializer.Serialize(this);

        public static MyType Parse (string s, IFormatProvider? provider) => JsonSerializer.Deserialize<MyType>(s) ?? throw new ArgumentException();

        public static bool TryParse (string? s, IFormatProvider? provider, out MyType result) => throw new NotImplementedException("not needed for the question");

    }

​

    public sealed class ParsableSurrogate<TSelf> where TSelf : IParsable<TSelf>

    {

        [IgnoreDataMember]

        public TSelf? Value { get; set; }

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        public string? TextValue { get { return Value?.ToString(); } set { Value = (value == null ? default : TSelf.Parse(value, default)); } }

    }

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    public class SerializationSurrogateProvider : ISerializationSurrogateProvider

    {

        readonly Dictionary<Type, (Type SurrogateType, Func<object, Type, object> ToSurrogate)> toSurrogateDictionary = new();

        readonly Dictionary<Type, (Type OriginalType, Func<object, Type, object> ToOriginal)> fromSurrogateDictionary = new();

        public Type GetSurrogateType(Type type) =>

            toSurrogateDictionary.TryGetValue(type, out var entry) ? entry.SurrogateType : type;

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        // TODO: check to see whether null objects are handled correctly

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        public object GetObjectToSerialize(object obj, Type targetType) =>

            toSurrogateDictionary.TryGetValue(obj.GetType(), out var entry) ? entry.ToSurrogate(obj, targetType) : obj;

​

        public object GetDeserializedObject(object obj, Type targetType) =>

            fromSurrogateDictionary.TryGetValue(obj.GetType(), out var entry) ? entry.ToOriginal(obj, targetType) : obj;

        public SerializationSurrogateProvider AddParsable<TParsable>() where TParsable : IParsable<TParsable>

        {

            toSurrogateDictionary.Add(typeof(TParsable), (typeof(ParsableSurrogate<TParsable>), (obj, t) => new ParsableSurrogate<TParsable> { Value = (TParsable)obj }));

            fromSurrogateDictionary.Add(typeof(ParsableSurrogate<TParsable>), (typeof(TParsable), (obj, t) => ((ParsableSurrogate<TParsable>)obj).Value!));

            return this;

        }

    }

​

    public class Model

    {

        public List<MyType?> MyTypes { get; set; } = new ();

    }

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    class TestClass

    {

        public static void Test()

        {

            TestMyType();

            Console.WriteLine();

            TestNested();

        }

        public static void TestMyType()

        {

            var model = new MyType("hello", "there");

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            var serializer = new DataContractSerializer(model.GetType());

            serializer.SetSerializationSurrogateProvider(new SerializationSurrogateProvider().AddParsable<MyType>());

            var xml = model.ToContractXml(serializer : serializer);

            var model2 = DataContractSerializerHelper.FromContractXml<MyType>(xml, serializer);

            Console.WriteLine(xml);

            Assert.That(model.Value1 == model2?.Value1 && model.Value2 == model2?.Value2);

        }

        public static void TestNested()

        {

            var model = new Model

            {

                MyTypes = { new MyType("hello", "there"), null, new MyType("foo", "bar") },

            };

            var serializer = new DataContractSerializer(model.GetType());

            serializer.SetSerializationSurrogateProvider(new SerializationSurrogateProvider().AddParsable<MyType>());

            var xml = model.ToContractXml(serializer : serializer);

            var model2 = DataContractSerializerHelper.FromContractXml<Model>(xml, serializer);

            Console.WriteLine(xml);

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            Assert.That(model2 != null);

            Assert.AreEqual(model.MyTypes.Count, model2?.MyTypes.Count);

            Assert.That(model.MyTypes.Select(m => m?.ToString()).SequenceEqual(model2!.MyTypes.Select(m => m?.ToString())));

            var xml2 = model2.ToContractXml(serializer : serializer);

            Assert.AreEqual(xml, xml2);

        }   

    }

​

    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();

            }

        }

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        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);

            }

        }

    }

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    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();

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            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​