字母加随机数字编号

private string getAplusRandom(){    string strFive = CreateRandom();    DataSet ds = rule.GetOne(strFive);    if (ds.Tables[0].Rows.Count == 0)    {    }    else    {        getAplusRandom();    }    return strFive;}private static char[] ConstantNumber = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };protected string CreateRandom(){    Random rd = new Random();    System.Text.StringBuilder strFiveChars = new System.Text.StringBuilder(6);    strFiveChars.Append("A");    for (int i = 0; i < 5; i++)    {        strFiveChars.Append(ConstantNumber[rd.Next(10)]);    }    strFive = strFiveChars.ToString();    return strFive;}