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.Runtime.Serialization;

using System.Runtime.Serialization.Formatters.Binary;

using System.IO.Compression;

using System.Reflection;

​

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

​

//https://stackoverflow.com/questions/59266201/unable-to-serialize-array-object-in-c-sharp

​

    public partial class ct_ServiceProductInfoWireless 

    {

        private object[] itemsField;

​

        /// <remarks/>

        [System.Xml.Serialization.XmlElementAttribute("NewWirelessLines", typeof(ct_WirelessLines))]

        [System.Xml.Serialization.XmlElementAttribute("WirelessLine", typeof(ct_ServiceProductInfoWirelessWirelessLine))]

        public object[] Items {

            get {

                return this.itemsField;

            }

            set {

                this.itemsField = value;

            }

        }

    }

​

    public partial class ct_WirelessLines

    {

    }

​

    public partial class ct_ServiceProductInfoWirelessWirelessLine

    {

    }

​

    public class TestClass

    {

        static string GetXml<T>(T objectToSerialize)

        {

            var stringWriter = new System.IO.StringWriter();

            var serializer = new XmlSerializer(objectToSerialize.GetType());

            serializer.Serialize(stringWriter, objectToSerialize); //Getting exception here

            return stringWriter.ToString();

        }

        static IEnumerable<ct_WirelessLines> GetWirelessLines()

        {

            return new [] { new ct_WirelessLines() };

        }

        static IEnumerable<ct_ServiceProductInfoWirelessWirelessLine> GetProductInfoWirelessWirelessLines()

        {

            return new [] { new ct_ServiceProductInfoWirelessWirelessLine() };

        }

        public static void Test()

        {

            var wirelessLines = GetWirelessLines(); // Some IEnumerable<ct_WirelessLines>

            var productInfo = GetProductInfoWirelessWirelessLines(); // Some IEnumerable<ct_ServiceProductInfoWirelessWirelessLine>

            var objectToSerialize = new ct_ServiceProductInfoWireless

            {

                Items = wirelessLines.Cast<object>().Concat(productInfo).ToArray(),

            };

            var xml = GetXml(objectToSerialize);

            Console.WriteLine(xml);

        }

    }

​

    public class Program

    {

        public static void Main()

        {

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

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

        public static string GetNetCoreVersion()

        {

            //https://techblog.dorogin.com/how-to-detect-net-core-version-in-runtime-ecd65ad695be

            //

            var assembly = typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly;

            var assemblyPath = assembly.CodeBase.Split(new[] { '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);

            int netCoreAppIndex = Array.IndexOf(assemblyPath, "Microsoft.NETCore.App");

            if (netCoreAppIndex > 0 && netCoreAppIndex < assemblyPath.Length - 2)

                return assemblyPath[netCoreAppIndex + 1];

            return null;

        }

    }

​

#if false

I was able to get the error message `System.InvalidOperationException: The type ct_WirelessLines[] may not be used in this context.` by assigning `ct_ServiceProductInfoWireless.Items` to be an array of array of `ct_WirelessLines` instead of a 1d array:  `Items = new [] { new [] { new ct_WirelessLines() } }`.  Demo fiddle: https://dotnetfiddle.net/PaXdUR.  The code compiles because `Items` is just an array of objects, but won't serialize because `XmlSerializer` expects only the objects of the two declared types in the array, and not some nested array.  Could you be doing that?

#endif

​

​