C#生成不重复随机字符串类

using System;namespace DotNet.Utilities{  public class RandomOperate  {    // 一：随机生成不重复数字字符串     private int rep = 0;    public string GenerateCheckCodeNum(int codeCount)    {      string str = string.Empty;      long num2 = DateTime.Now.Ticks + this.rep;      this.rep++;      Random random = new Random(((int)(((ulong)num2) & 0xffffffffL)) | ((int)(num2 >> this.rep)));      for (int i = 0; i < codeCount; i++)      {        int num = random.Next();        str = str + ((char)(0x30 + ((ushort)(num % 10)))).ToString();      }      return str;    }    //方法二：随机生成字符串（数字和字母混和）    public string GenerateCheckCode(int codeCount)    {      string str = string.Empty;      long num2 = DateTime.Now.Ticks + this.rep;      this.rep++;      Random random = new 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;    }    #region    /// <summary>    /// 从字符串里随机得到，规定个数的字符串.    /// </summary>    /// <param name="allChar"></param>    /// <param name="CodeCount"></param>    /// <returns></returns>    private string GetRandomCode(string allChar, int CodeCount)    {      //string allChar = "1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,i,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z";      string[] allCharArray = allChar.Split(',');      string RandomCode = "";      int temp = -1;      Random rand = new Random();      for (int i = 0; i < CodeCount; i++)      {        if (temp != -1)        {          rand = new Random(temp * i * ((int)DateTime.Now.Ticks));        }        int t = rand.Next(allCharArray.Length - 1);        while (temp == t)        {          t = rand.Next(allCharArray.Length - 1);        }        temp = t;        RandomCode += allCharArray[t];      }      return RandomCode;    }    #endregion  }}