随机函数

下面这段代码是自己写的一段程序段,主要功能是在一个确定的路径下面随机搜索n个项目.

protected void Button1_Click(object sender, EventArgs e)
    {
        try
        {
            Label3.Visible = true;
            Label3.Text = "";
            TableRow tr;
            TableCell tc;
            Random autoRand = new Random();
            ArrayList arr = new ArrayList();
            double percentage = Convert.ToInt32(TextBox3.Text);
            percentage = percentage / 100;

            string name = TextBox1.Text;
            string str = "D:\\XXX\\" + name + "\\";
            int num = 0;

            DirectoryInfo dir = new DirectoryInfo(str);

            foreach (FileSystemInfo fsi in dir.GetFileSystemInfos())
            {
                filename = "";
                if (fsi is FileInfo)
                {
                    num++;
                    filename = fsi.FullName;
                    arr.Add(filename);
                }
                if (fsi is DirectoryInfo)
                {
                    num++;
                    filename = fsi.FullName;
                    arr.Add(filename);
                }
            }

            for (double i = 1; i <=percentage * num; i += 1)
            {
                int sum =Convert.ToInt32(percentage * num);
                foreach (FileSystemInfo fsi in dir.GetFileSystemInfos())
                {
                    filename = arr[autoRand.Next(1, num)].ToString();
                    tr = new TableRow();
                    tc = new TableCell();
                    tc.Controls.Add(new LiteralControl(filename.ToString()));
                    tr.Cells.Add(tc);

                    Table1.Rows.Add(tr);
                    break;
                }
            }
        }
        catch
        {
            Label3.Text = "不存在该项目,请确定后重新搜索!";
        }
    }