Не сохраняет xml-файл - C#

Формулировка задачи:

Вот часть кода:

public class MainFileGlobals
    {
        public const string MainFileName = "MainFile.xml";
        
        public const string MainFileElementSt = "MainFile";
        public const string TimeElementSt = "Time";
        public const string DateElementSt = "Date";
        public const string DescriptionElementSt = "Description";
        public const string DeleteElementSt = "Delete";
        
        public const string DescriptionInner = "Главный файл";
        
        public static FileStream xml_main_file;
        public static XmlTextWriter xml_main_writer;
        public static XmlDocument xml_main_doc;
        
        public static XmlNode TimeElement;
        public static XmlNode DateElement;
        public static XmlNode DescriptionElement;
        public static XmlNode DeleteElement;
        
    }

Вот вторая:

public static void CreateMainXML()
        {
            if (File.Exists(MainFileGlobals.MainFileName))
            {
                MainFileGlobals.xml_main_writer = new XmlTextWriter(MainFileGlobals.MainFileName,Encoding.UTF8);
                
                MainFileGlobals.xml_main_writer.WriteStartDocument();
                MainFileGlobals.xml_main_writer.WriteStartElement(MainFileGlobals.MainFileElementSt);
                MainFileGlobals.xml_main_writer.WriteEndElement();
                MainFileGlobals.xml_main_writer.Close();
                
                MainFileGlobals.xml_main_doc = new XmlDocument();
                
                MainFileGlobals.xml_main_doc.Load(MainFileGlobals.MainFileName);
                
                MainFileGlobals.DateElement = MainFileGlobals.xml_main_doc.CreateElement(MainFileGlobals.DateElementSt);
                MainFileGlobals.DateElement.InnerText = DateTime.Now.ToString();
                
                MainFileGlobals.DeleteElement = MainFileGlobals.xml_main_doc.CreateElement(MainFileGlobals.DeleteElementSt);
                MainFileGlobals.DescriptionElement.InnerText = MainFileGlobals.DescriptionInner;
                
                MainFileGlobals.xml_main_file = new FileStream(MainFileGlobals.MainFileName,FileMode.Append);
                
                MainFileGlobals.xml_main_doc.Save(MainFileGlobals.xml_main_file);
            }
        }

Вот 3:

if (!File.Exists(MainFileGlobals.MainFileName))
            {
                try
                {
                    Model.CreateMainXML();
                    MessageBox.Show(MainFileGlobals.MainFileName+" создан","Warning",MessageBoxButtons.OK,MessageBoxIcon.Warning);
                }
                catch(Exception ex)
                {
                    MessageBox.Show(ex.Message,"Error",MessageBoxButtons.OK,MessageBoxIcon.Error);
                }
                    
            }

Решение задачи: «Не сохраняет xml-файл»

textual
                            Листинг программы 
                        

                            public static void CreateMainXML()
{
    XDocument xdoc = new XDocument(new XElement("HEADER",
        new XElement("MainFile", 
            new XElement("Date", DateTime.Now.ToString()),
            new XElement("Delete", MainFileGlobals.DeleteInner),
            new XElement("Description", MainFileGlobals.DescriptionInner)
        )
    ));
    xdoc.Save(MainFileGlobals.MainFileName);
}
 
public class MainFileGlobals
{
    public const string MainFileName = "MainFile.xml";
    
    public const string DescriptionInner = "Главный файл";
    public const string DeleteInner = "false";
}
                        