winform关闭窗体友好提示！

 1  private void Form1_FormClosing(object sender, FormClosingEventArgs e)
 2         {
 3             DialogResult dr = MessageBox.Show("系统提示", "是否退出？", MessageBoxButtons.YesNo, MessageBoxIcon.Information);
 4             if (dr == DialogResult.Yes)
 5             {
 6                 System.Environment.Exit(0);
 7             }
 8             else
 9                 e.Cancel = true;//取消事件的值
10         }