/// <summary>
        /// 獲取文件的MD5碼
        /// </summary>
        /// <param name="filePath">文件路徑</param>
        /// <returns>MD5碼</returns>
        private static string GetFileMD5(string filePath)
        {
            try
            {
                var file = new FileStream(filePath, FileMode.Open);
                MD5 md5 
 
= new MD5CryptoServiceProvider();
                var retval = md5.ComputeHash(file);
                file.Close();

                var stringBuilder = new StringBuilder();
                foreach (var t in retval)
                {
                    stringBuilder.Append(t.ToString("x2"));
                }
                
 
return stringBuilder.ToString();
            }
            catch (Exception)
            {
                return null;
            }
        }

獲取文件的MD5碼