//按钮触发事件

 private void button25_Click(object sender, EventArgs e)
 {
         ShowMessage("测试弹框！！！");
 }

//调用弹窗方法

 private void ShowMessage(string sMsg)
 {
     // 创建一个线程来执行倒计时操作
     Thread thread = new Thread(() =>
     {
         // 倒计时几秒关闭，我这里设置的5秒自动关闭
         Thread.Sleep(5000);
         // 关闭MessageBox
         if (InvokeRequired)
         {
             Invoke(new System.Action(() => { CloseMessageBox(); }));
         }
         else
         {
             CloseMessageBox();
         }
     });
     // 启动线程
     thread.Start();
     // 弹出MessageBox提示框，注意：这里的标题必须与下方查找关闭MessageBox里的标题一致。
     MessageBox.Show(sMsg, "完成提示");
 }

//关闭弹窗方法

  // 查找窗口
  [System.Runtime.InteropServices.DllImport("user32.dll", SetLastError = true)]
  private static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
  // 发送消息
  [System.Runtime.InteropServices.DllImport("user32.dll", CharSet = System.Runtime.InteropServices.CharSet.Auto)]
  private static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);

  // 关闭消息
  private const uint WM_CLOSE = 0x0010;
///关闭弹窗方法
 private void CloseMessageBox()
 {
     // 查找并关闭MessageBox窗口
     IntPtr hwnd = FindWindow(null, "完成提示");//一致
     if (hwnd != IntPtr.Zero)
     {
         SendMessage(hwnd, WM_CLOSE, IntPtr.Zero, IntPtr.Zero);
     }
 }