protected override void WndProc(ref Message msg)
        {
            const int WM_SYSCOMMAND = 0x0112;
            const int SC_CLOSE = 0xF060;

            if (msg.Msg == WM_SYSCOMMAND && ((int)msg.WParam == SC_CLOSE))
            {
                // 点击winform右上关闭按钮 
                // 加入想要的逻辑处理
                MessageBox.Show("弹出Form3窗体");
                Form3 form = new Form3();
                form.Show();
                //return;//阻止了窗体关闭
            }
            base.WndProc(ref msg);
        }