随机得到，规定个数的字符串

     #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