生成随机字母字符串(数字字母混和)

/// 生成随机字母字符串(数字字母混和)
///
/// 待生成的位数
/// 生成的字母字符串
private string GenerateCheckCode(int codeCount)
{
int rep = 0;
string str = string.Empty;
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;
}