一些实用的方法，持续更新...

/// <summary>  
        /// Md5加密
        /// </summary>  
        /// <param name="strSource">待加密字串</param>  
        /// <param name="length">16或32值之一,其它则采用.net默认MD5加密算法</param>  
        /// <returns>加密后的字串</returns>  
        public static string MD5Encrypt(string strSource, int length = 0)
        {
            byte[] bytes = Encoding.UTF8.GetBytes(strSource);
            byte[] hashValue = ((System.Security.Cryptography.HashAlgorithm)System.Security.Cryptography.CryptoConfig.CreateFromName("MD5")).ComputeHash(bytes);
            StringBuilder sb = new StringBuilder();
            switch (length)
            {
                case 16:
                    for (int i = 4; i < 12; i++)
                        sb.Append(hashValue[i].ToString("x2"));
                    break;
                case 32:
                    for (int i = 0; i < 16; i++)
                    {
                        sb.Append(hashValue[i].ToString("x2"));
                    }
                    break;
                default:
                    for (int i = 0; i < hashValue.Length; i++)
                    {
                        sb.Append(hashValue[i].ToString("x2"));
                    }
                    break;
            }
            return sb.ToString();
        }

 /// <summary>
        /// 隐藏手机号中间4位
        /// </summary>
        /// <param name="mobile"></param>
        /// <returns></returns>
        public static string ParserMobile(string mobile)
        {
            if (string.IsNullOrEmpty(mobile)) return string.Empty;
            if (mobile.Length != 11) return mobile;
            var start = mobile.Substring(0, 3);
            var end = mobile.Substring(mobile.Length - 4, 4);
            return string.Format("{0}****{1}", start, end);
        }

/// <summary>
        /// 格式化QueryString
        /// </summary>
        /// <param name="queryString"></param>
        /// <returns></returns>
        public static NameValueCollection PaserToKeyValue(string queryString)
        {
            try
            {
                var coll = System.Web.HttpUtility.ParseQueryString(queryString);
                return coll;
            }
            catch { }
            return null;
        }

/// <summary>
        /// 字符串转Int
        /// </summary>
        /// <param name="val"></param>
        /// <returns></returns>
        public static int ToInt(string val)
        {
            int i;
            int.TryParse(val,out i);
            return i;
        }

/// <summary>
        /// 字符串转Int64
        /// </summary>
        /// <param name="val"></param>
        /// <returns></returns>
        public static long ToInt64(string val)
        {
            long v;
            if (!long.TryParse(val, out  v))
            {
                v = 0;
            }
            return v;
        }

/// <summary>
        /// 字符串转Int?
        /// </summary>
        /// <param name="val"></param>
        /// <returns></returns>
        public static int? ToNullInt(string val)
        {
            int? i;
            try
            {
                i = Convert.ToInt32(val);
            }
            catch
            {
                i = null;
            }
            return i;
        }

/// <summary>
        /// HtmlToStr
        /// </summary>
        /// <param name="htmlstring"></param>
        /// <param name="replaceto"></param>
        /// <returns></returns>
        public static string HtmlToString(string htmlstring, string replaceto = " ")
        {
            if (string.IsNullOrEmpty(htmlstring)) return string.Empty;
            //删除脚本   
            htmlstring =
                Regex.Replace(htmlstring, @"<script[^>]*?>.*?</script>",
                "", RegexOptions.IgnoreCase);
            //删除HTML   
            htmlstring = Regex.Replace(htmlstring, @"<(.[^>]*)>", "", RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"([
])[s]+", "", RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"-->", "", RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"<!--.*", "", RegexOptions.IgnoreCase);

            htmlstring = Regex.Replace(htmlstring, @"&(quot|#34);", """, RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"&(amp|#38);", "&", RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"&(lt|#60);", "<", RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"&(gt|#62);", ">", RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"&(nbsp|#160);", "   ", RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"&(iexcl|#161);", "xa1", RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"&(cent|#162);", "xa2", RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"&(pound|#163);", "xa3", RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"&(copy|#169);", "xa9", RegexOptions.IgnoreCase);
            htmlstring = Regex.Replace(htmlstring, @"&#(d+);", "", RegexOptions.IgnoreCase);

            htmlstring = htmlstring.Replace("<", "");
            htmlstring = htmlstring.Replace(">", "");
            htmlstring = htmlstring.Replace("
", "");
            return htmlstring;
        }

/// <summary>
        /// 替换字符
        /// </summary>
        /// <param name="str"></param>
        /// <param name="length"></param>
        /// <param name="endstr"></param>
        /// <returns></returns>
        public static string Replace(string str, int length, string endstr = "...")
        {
            if (!string.IsNullOrEmpty(str))
            {
                if (str.Length > length)
                {
                    str = str.Substring(0, length) + endstr;
                }
            }
            return str;
        }

/// <summary>
        /// 查询Config值
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <returns></returns>
        public static T GetAppSetting<T>(string key)
        {
            try
            {
                var val = ConfigurationManager.AppSettings[key];
                return StringHelper.ChangeType<T>(val);
            }
            catch
            {
                return default(T);
            }
        }

/// <summary>
        /// 更改类型
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="v"></param>
        /// <returns></returns>
        public static T ChangeType<T>(object v)
        {
            try
            {
                return (T)Convert.ChangeType(v, typeof(T));
            }
            catch
            {
                return default(T);
            }
        }