C# 窗口关闭事件

//退出按键
     private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            DialogResult dr = MessageBox.Show("是否退出?", "提示:", MessageBoxButtons.OKCancel, MessageBoxIcon.Information);  

            if (dr == DialogResult.OK)   //如果单击“是”按钮
            {
                e.Cancel = false;                 //关闭窗体
            }
            else if (dr == DialogResult.Cancel)
            {
                e.Cancel = true;                  //不执行操作
            }
        }

窗体属性面框，选择上面像闪电的标示

找到窗口关闭事件，选择Form1_FormClosing方法