private static readonly Random Random = new Random();

        /// <summary>
        /// 生成随机数字
        /// </summary>
        /// <param name="length">生成长度</param>
        /// <returns></returns>
        public static string Number(int length)
        {
            return Number(length, false);
        }

        /// <summary>
        /// 生成随机数字
        /// </summary>
        /// <param name="length">生成长度</param>
        /// <param name="sleep">是否要在生成前将当前线程阻止以避免重复</param>
        /// <returns></returns>
        public static string Number(int length, bool sleep)
        {
            if (sleep)
                System.Threading.Thread.Sleep(2);
            string result = "";

            for (int i = 0; i < length; i++)
            {
                result += Random.Next(10).ToString();
            }
            return result;
        }
        /// <summary>
        /// 生成随机字母字符串(数字字母混和)
        /// </summary>
        /// <param name="codeCount">待生成的位数</param>
        public static string GetCheckCode(int codeCount)
        {
            string str = string.Empty;
            int rep = 0;
            long num2 = DateTime.Now.Ticks + rep;
            rep++;
            Random random = new Random(((int)(((ulong)num2) & 0xffffffffL)) | ((int)(num2 >> rep)));
            for (int i = 0; i < codeCount; i++)
            {
                char ch;
                int num = random.Next();
                if ((num % 2) == 0)
                {
                    ch = (char)(0x30 + ((ushort)(num % 10)));
                }
                else
                {
                    ch = (char)(0x41 + ((ushort)(num % 0x1a)));
                }
                str = str + ch.ToString();
            }
            return str;
        }