void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
if (MessageBox.Show(
"窗口关闭后，数据即将丢失！是否现在关闭窗口",
"提示", 
            MessageBoxButtons.OKCancel, 
            MessageBoxIcon.Question) != DialogResult.OK)
            {
                e.Cancel = true;
return;
            }
}