DateFormatter - ICustomFormatter

public void Formatting_test() {

            Console.WriteLine(string.Format(MyDateFormatter.Create(),"Today's date      [ds]  ->  {0,-20:ds}",DateTime.Now));

            Console.WriteLine(string.Format(MyDateFormatter.Create(),"Today's file date [ddf] ->  {0,-60:ddf}",DateTime.Now));
            Console.WriteLine(string.Format(MyDateFormatter.Create(),"Today's file time [ddb] ->  {0,-60:ddb}",DateTime.Now));

            Console.WriteLine(string.Format(MyDateFormatter.Create(),"Today's file date [fd]  ->  {0,-60:fd}",DateTime.Now));
            Console.WriteLine(string.Format(MyDateFormatter.Create(),"Today's file time [ft]  ->  {0,-60:ft}",DateTime.Now));
        }

        public class MyDateFormatter:IFormatProvider,ICustomFormatter {
            public static MyDateFormatter Create() {
                return new MyDateFormatter();
            }
            IFormatProvider _parent;   // Allows consumers to chain format providers

            public MyDateFormatter() : this(CultureInfo.CurrentCulture) { }

            public MyDateFormatter(IFormatProvider parent) {
                _parent = parent;
            }

            public object GetFormat(Type formatType) {
                if(formatType == typeof(ICustomFormatter))
                    return this;
                return null;
            }

            public string Format(string format,object arg,IFormatProvider formatProvider) {

                bool ignore = false;
                string[] tokens = new string[] {"ds","ddf","ddb","fd","ft" };
                string formatLowered = format.ToLowerInvariant();

                if(arg == null)
                    ignore = true;
                else {
                    if(!tokens.Contains(formatLowered))
                        ignore = true;
                }

                DateTime dtarget = DateTime.MinValue;

                if(!ignore) {

                    if(arg is DateTime)
                        dtarget = Convert.ToDateTime(arg);
                    else {
                        if(!DateTime.TryParse(arg.ToString(),out dtarget))
                            ignore = true;
                    }
                }
                if(ignore)
                    return string.Format(_parent,"{0:" + (format == "" ? "D": format) + "}",arg);

                if(formatLowered == "ds") {
                    return dtarget.ToShortDateString();
                }
                else if(formatLowered == "ddf" || formatLowered == "fd") {
                    //"Mar31_2011";
                    return dtarget.ToString("MMMdd_yyyy");
                }
                else if(formatLowered == "ddb" || formatLowered == "ft") {
                    return dtarget.ToString("MMM_d_yyyy_hmmtt");
                }

                return dtarget.ToString();

            }
        }