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;             } }