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/57287775/xdocument-write-specific-xelement-in-a-signle-line

​

    public class CustomFormattingXmlTextWriter : XmlTextWriter

    {

        readonly Stack<Formatting> stack = new Stack<Formatting>();

        public CustomFormattingXmlTextWriter(TextWriter writer, int indentDepth) : base(writer) 

        { 

            this.Formatting = Formatting.Indented; 

            this.IndentDepth = indentDepth;

        }

        int IndentDepth { get; }

​

        void OnElementStarted(string localName, string ns)

        {

            stack.Push(Formatting);

            // You could e.g. modify the logic here to check to see whether localName == CHILDELEMENT

            // if (localName == "CHILDELEMENT")

            if (stack.Count == IndentDepth+1)

                Formatting = Formatting.None;

        }

​

        void OnElementEnded()

        {

            var old = stack.Pop();

            if (old != Formatting)

                Formatting = old;

        }

​

        public override void WriteStartElement(string prefix, string localName, string ns)

        {

            base.WriteStartElement(prefix, localName, ns);

            OnElementStarted(localName, ns);

        }

​

        public override void WriteEndElement()

        {

            base.WriteEndElement();

            OnElementEnded();

        }

        public override void WriteFullEndElement()

        {

            base.WriteEndElement();

            OnElementEnded();

        }

    }

​

    public static partial class XNodeExtensions

    {

        public static void SaveWithCustomFormatting(this XDocument doc, string filename, int indentDepth)

        {

            using (var textWriter = new StreamWriter(filename))

            using (var writer = new CustomFormattingXmlTextWriter(textWriter, indentDepth))

            {

                doc.Save(writer);

            }

        }

    }

​

    public class TestClass

    {

        public static void Test()

        {

            var fileName = "Question57287775.xml";

            var myDoc = new XDocument(new XElement("ROOTELEMENT",

                                                   new XElement("CHILDELEMENT",

                                                                new XElement("INFO1", "Test a 1"),

                                                                new XElement("INFO2", "Test a 2")),

                                                   new XElement("CHILDELEMENT",

                                                                new XElement("INFO1", "Test b 1"),

                                                                new XElement("INFO2", "Test b 2")),

                                                   new XElement("CHILDELEMENT")

                                                  ));

​

            myDoc.SaveWithCustomFormatting(fileName, 1);

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

        }

    }

​

    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;

        }

    }

​