菜鸟请请教高手，在C#中我用Clipboard.Clear(),清空了剪贴板，可是我复制几次之后，剪贴板上的内容也会复制好几次呢。求教，多谢！

   private void button2_Click(object sender, EventArgs e)
        {
            Clipboard.Clear();
            for (int i = 0; i < listBox1.Items.Count; i++)
            {

                s += listBox1.Items[i].ToString() + '\n';

            }
           
            try
            {

                Clipboard.SetDataObject(s, true, 1, 9999);

            }
            catch (Exception ex)
            {
                MessageBox.Show("出错了:{0}",ex.Message);
            }
            finally { MessageBox.Show("已复制！"); }