随机数 字母 数字

//len:随机数长度。beginRange，endRange：为"0123456789abcdefghigklmnopqrstuvwxyzABCDEFGHIGKLMNOPQRSTUVWXYZ"这段字符串的范围

private string GetRandomCharNum(int len, int beginRange, int endRange)
{
string ret = null;
string str = @"0123456789abcdefghigklmnopqrstuvwxyzABCDEFGHIGKLMNOPQRSTUVWXYZ";
var seed = Guid.NewGuid().GetHashCode();
Random random = new Random(seed);
for (int i = 0; i < len; i++)
{
ret += str.Substring(beginRange + random.Next(endRange), 1);
}
return ret;
}