Random生成随机字母字符串(数字字母混和)

　 private int rep = 0;

    /// <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>
    /// <returns>生成的字母字符串</returns>
    private string GenerateCheckCode(int codeCount)
    {
        string str = string.Empty;
        long num2 = DateTime.Now.Ticks + this.rep;
        this.rep++;
        System.Random random = new System.Random(((int)(((ulong)num2) & 0xffffffffL)) | ((int)(num2 >> this.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;
    }