questions/45358844/c-sharp-xml-serializer-deserializes-list-to-count-of-0-instead-of-null

CSharp · Console

/Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml.Serialization;
using System.Xml;
using System.IO;
using System.Diagnostics;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Xml.Linq;
using System.Reflection;
using System.Data;
using System.Xml.Schema;
using System.Text.RegularExpressions;
using System.Net;
using System.Xml.XPath;
using System.Globalization;
using System.ComponentModel.DataAnnotations;
using System.Collections;
using System.Runtime.InteropServices;
using System.Runtime.Serialization;
using System.Threading.Tasks;


// https://stackoverflow.com/questions/45358844/c-sharp-xml-serializer-deserializes-list-to-count-of-0-instead-of-null


    [XmlRootAttribute("MyClass", Namespace = "", IsNullable = false)]
    public class MyClass
    {
        private string comments;
        public string Comments
        {
            set { comments = value; }
            get { return comments; }
        }

        private System.Collections.Generic.List<string> tests = null;

        [XmlIgnore]
        public System.Collections.Generic.List<string> Tests
        {
            get { return tests; }
            set { tests = value; }
        }

        [XmlArray("Tests")]
        public string[] TestsArray
        {
            get
            {
                return (Tests == null ? null : Tests.ToArray());
            }
            set
            {
                if (value == null)
                    return;
                (Tests = Tests ?? new List<string>(value.Length)).AddRange(value);
            }
        }
    }


    class TestClass
    {
        public static void Test()
        {
            foreach (var tuple in GetXml())
                Test(tuple);
            Console.WriteLine("Tests complete.");
        }

        static void Test(Tuple<string, List<string>> tuple)
        {
            var xml = tuple.Item1;

            Console.WriteLine("Input XML: ");
            Console.WriteLine(xml);

            var myClass = xml.LoadFromXml<MyClass>();

            Console.WriteLine("myClass.Tests = {0}", myClass.Tests == null ? "null" : myClass.Tests.Count.ToString());

            Console.WriteLine("Re-serialized XML: ");
            Console.WriteLine(myClass.GetXml(true));

            Assert.IsTrue(ListsSame(myClass.Tests, tuple.Item2));
            Console.WriteLine("Contents of myClass.Tests are correct.\n");
        }
		
        static bool ListsSame<T>(ICollection<T> list1, ICollection<T> list2)
        {
            if (object.ReferenceEquals(list1, list2))
                return true;
            else if (object.ReferenceEquals(list1, null) || object.ReferenceEquals(list2, null))
                return false;
            return list1.SequenceEqual(list2);
        }

        static IEnumerable<Tuple<string, List<string>>> GetXml()
        {
            return new[]
            {
                Tuple.Create(@"<MyClass>
  <SomeNode>value</SomeNode>
</MyClass>", (List<string>)null),

                Tuple.Create(@"<MyClass>
</MyClass>", (List<string>)null),

                Tuple.Create(@"<MyClass>
  <SomeNode>value</SomeNode>
  <Tests />
</MyClass>", new List<string>()),

                Tuple.Create(@"<MyClass>
  <SomeNode>value</SomeNode>
  <Tests></Tests>, 
</MyClass>", new List<string>()),

           Tuple.Create(@"<MyClass>
  <SomeNode>value</SomeNode>
  <Tests>
    <string>hello</string>
    <string>goodbye</string>
  </Tests>
</MyClass>", new List<string> { "hello", "goodbye" }),
            };
        }
    }
					
    public static class XmlSerializationHelper
    {
        public static T LoadFromXml<T>(this string xmlString, XmlSerializer serial = null)
        {
            serial = serial ?? new XmlSerializer(typeof(T));
            T returnValue = default(T);
            using (StringReader reader = new StringReader(xmlString))
            {
                object result = serial.Deserialize(reader);
                if (result is T)
                {
                    returnValue = (T)result;
                }
            }
            return returnValue;
        }

        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 AssertionFailedException : System.Exception
    {
        public AssertionFailedException() : base() { }

        public AssertionFailedException(string s) : base(s) { }
    }

    public static class Assert
    {
        public static void IsTrue(bool value)
        {
            if (value == false)
                throw new AssertionFailedException("failed");
        }
    }

	public class Program
	{
		public static void Main()
		{
			TestClass.Test();
		}
	}