Genericsの要素をComparisonで並べ替え

Comparisonには-1,0,1の3つを返す関数を登録する

            List<FileInfo> files = new List<FileInfo>();
            foreach (FileInfo file in dir.GetFiles("*.jpg"))
            {
                files.Add(file);
            }

            Comparison<FileInfo> comp = new Comparison<FileInfo>(delegate(FileInfo a, FileInfo b)
            {
                int an = extractInt(a.Name);
                int bn = extractInt(b.Name);
                if (an > bn) return 1;
                else if (an == bn) return 0;
                else return -1;
            });
            files.Sort(comp);

正規表現が苦手

        public static int extractInt(String str)
        {
            String num = "";
            bool numFounded = false;
            foreach (char c in str.ToCharArray())
            {
                if (Regex.IsMatch(new String(c, 1), "[0-9]"))
                {
                    num += c;
                    numFounded = true;
                }
                else if (numFounded) // 文字→数字→文字と来た時
                {
                    break;
                }
            }
            try
            {
                return int.Parse(num);
            }
            catch
            {
                return -1;
            }
        }