DataLayer

   public class UrlStorage
   {
      /// <summary>
      /// Message string
      /// </summary>
      public static string messages;

      /// <summary>
      /// Path to XML File
      /// </summary>
      public const string FILEXML = @"D:\somewhere\example.xml";



      /// <summary>
      /// private constructor of UrlStorage
      /// useful to avoid creating instance of it
      /// </summary>
      private UrlStorage() {
      }

      /// <summary>
      /// singleton pattern
      /// </summary>
      public static readonly UrlStorage instance = new UrlStorage();

      /// <summary>
      /// read XML file
      /// </summary>
      public List<CategoriesCtrlDto> readXMLtoLIST()
      {
         List<CategoriesCtrlDto> CategoryList = null;

         try {

            if ( File.Exists( FILEXML ) ) {

               XmlDocument document = new XmlDocument();


               document.Load( FILEXML );

               XmlNodeList list_of_categories = document.SelectNodes( "/parent/Categories" );

               CategoryList = new List<CategoriesCtrlDto>();


               foreach ( XmlNode nodecategory in list_of_categories ) {


                  if ( nodecategory.HasChildNodes ) {

                     List<LinksCtrlDto> List1 = new List<LinksCtrlDto>();

                     //if yes then we can create a list of links
                     foreach ( XmlNode nodelinks in nodecategory.ChildNodes ) {
                        List1.Add( new LinksCtrlDto( nodelinks.Attributes["url"].Value, nodelinks.Attributes["name"].Value, nodelinks.Attributes["descr"].Value ) );
                     }

                     CategoriesCtrlDto categ = new CategoriesCtrlDto( nodecategory.Attributes["Name"].Value, List1 );
                     CategoryList.Add( categ );
                  }
               }
            } else {
               //if file not exists, return an empty list of categories
               CategoryList = new List<CategoriesCtrlDto>( 0 );
            }
            //we close the document
            //document.Save();
         } catch ( Exception e ) {
            //show exception message
            messages = e.Message;
         }

         return CategoryList;
      }


      /// <summary>
      /// Find a category name
      /// it is useful if you want to prevent adding duplicate category
      /// or check if the category name exists for remove process
      /// </summary>
      /// <param name="source"></param>
      /// <param name="search"></param>
      /// <param name="categ_name"></param>
      /// <param name="mode"></param>
      /// <returns></returns>
      private bool find_category(string source, string search) {
         bool result = false;
         XmlDocument document = new XmlDocument();

         try {
            if ( File.Exists( source ) ) {
               document.Load( source );

               foreach ( XmlNode category_nodes in document ) {
                  if ( ( category_nodes.Attributes["Name"].Value == search ) ) {
                     result = true;
                     break;
                  }
               }
            }
         } catch {
            throw;
         } finally {
            document.Save( source );
         }
         return result;
      }



      /// <summary>
      /// Find a category name
      /// it is useful if you want to prevent adding duplicate category
      /// or check if the category name exists for remove process
      /// </summary>
      /// <param name="source"></param>
      /// <param name="search"></param>
      /// <param name="categ_name"></param>
      /// <param name="mode"></param>
      /// <returns></returns>
      private bool find_link( string source, string search, string categ_name ) {
         bool result = false;
         XmlDocument document = new XmlDocument();

         try {
            if ( File.Exists( source ) ) {
               document.Load( source );

               foreach ( XmlNode categ_node in document ) {
                  XmlNodeList xnlist = document.SelectNodes( "/parent/Categories[@Name='" + categ_name + "']" );
                  foreach ( XmlNode link_nodes in categ_node ) {
                     if ( ( link_nodes.Attributes["url"].Value == search ) )
                        result = true;
                     break;
                  }
               }
            } else
               result = false;
         } catch {
            throw;
         } finally {
            document.Save( source );
         }
         return result;
      }


      /// <summary>
      /// add link to source file
      /// to a specified category
      /// </summary>
      /// <param name="source"></param>
      /// <param name="categoryname"></param>
      /// <param name="links"></param>
      /// <returns></returns>
      public bool add_link( string category_name, string url, string name, string description ) {
         bool result = false;

         XmlDocument document = new XmlDocument();
         XmlTextWriter writer = new XmlTextWriter( FILEXML, Encoding.UTF8 );

         if ( string.IsNullOrEmpty( category_name ) )
            throw new ArgumentNullException( "Add link to category name DL" );
         if ( string.IsNullOrEmpty( url ) )
            throw new ArgumentNullException( "Add link url name DL" );
         if ( string.IsNullOrEmpty( name ) )
            throw new ArgumentNullException( "Add link name DL" );
         if ( string.IsNullOrEmpty( description ) )
            throw new ArgumentNullException( "Add link description DL" );

         try {
            if ( File.Exists( FILEXML ) ) {
               document.Load( FILEXML );
               document.PreserveWhitespace = false;

               XmlNodeList xnlist = document.SelectNodes( "/parent/Categories[@Name='" + category_name + "']" );

               if ( xnlist.Count > 0 ) {

                  //if there are no duplicate then we can add link in XML file
                  if ( !find_link( FILEXML, url, category_name ) ) {
                     XmlElement element = document.CreateElement( "link" );
                     element.SetAttribute( "url", url );
                     element.SetAttribute( "name", name );
                     element.SetAttribute( "descr", description );
                     xnlist[0].AppendChild( element );
                     result = true;
                  } else {
                     result = false;
                  }

               } else
                  throw new ArgumentNullException( "xnlist empty DataLayer" );
            }
            if ( result ) {
               document.WriteTo( writer );
            }

         } catch {
            throw;
         } finally {
            document.Save( FILEXML );
         }

         return result;
      }

      /// <summary>
      /// Add a category into XML File
      /// First, we search it for duplicates
      /// </summary>
      /// <param name="source"></param>
      /// <param name="category"></param>
      /// <returns></returns>
      public bool add_category( string category_name ) {
         bool result = false;

         XmlDocument document = null;
         XmlTextWriter writer = null;

         if ( string.IsNullOrEmpty(category_name) )
            throw new ArgumentNullException( "categories" );

         try {
            if ( File.Exists( FILEXML ) ) {

               document = new XmlDocument();
               writer = new XmlTextWriter( FILEXML, Encoding.UTF8 );

               document.Load( FILEXML );
                  if ( !find_category( FILEXML, category_name ) ) {
                     XmlElement element = document.CreateElement( "Categories" );
                     element.SetAttribute( "Name", category_name );
                     result = true;
                  }
            } else
               result = false;

            //if is all ok then write data to XML file
            if ( result ) {
               document.WriteTo( writer );
            }
         } catch {
            throw;
         } finally {
            document.Save( FILEXML );
         }
         return result;
      }

      /// <summary>
      /// delete link if it has been found
      /// </summary>
      /// <param name="source"></param>
      /// <param name="category_name"></param>
      /// <param name="url"></param>
      /// <returns></returns>
      public bool delete_link( string category_name, string link_url ) {
         bool result = false;

         XmlDocument document = new XmlDocument();

         if ( string.IsNullOrEmpty(category_name) )
            throw new ArgumentNullException( "delete_link categories" );
         if ( string.IsNullOrEmpty( link_url ) )
            throw new ArgumentNullException( "delete_link DL" );

         try {
            if ( File.Exists( FILEXML ) ) {
               document.Load( FILEXML );

               if ( find_link( FILEXML, link_url, category_name ) ) {
                  XmlNode xnlist = document.SelectSingleNode( "/parent/Categories[@Name='" + category_name + "'/link[@url='" + link_url + "']" );
                  if ( xnlist != null ) {
                     xnlist.ParentNode.RemoveChild( xnlist );
                     result = true;
                  }
               }
            }
         } catch {
            throw;
         } finally {
            document.Save( FILEXML );
         }

         return result;
      }


      /// <summary>
      /// delete category if it has been found
      /// </summary>
      /// <param name="source"></param>
      /// <param name="category_name"></param>
      /// <param name="name"></param>
      /// <returns></returns>
      public bool delete_category( string category_name ) {
         bool result = false;

         XmlDocument document = new XmlDocument();

         if ( string.IsNullOrEmpty(category_name) )
            throw new ArgumentNullException("delete_category DL");

            try {
               if ( File.Exists( FILEXML ) ) {
                  document.Load( FILEXML );

                     if ( find_category( FILEXML, category_name ) ) {
                        XmlNode xnlist = document.SelectSingleNode( "/parent/Categories[@Name='" + category_name + "']" );
                        if ( xnlist != null ) {
                           xnlist.ParentNode.RemoveChild( xnlist );
                           result = true;
                        }
                  }
               }
            } catch {
               throw;
            } finally {
               document.Save( FILEXML );
            }

         return result;
      }
   }