来源：http://www.cftea.com/c/2013/11/6137.asp

 private void frmTest_Load(object sender, EventArgs e)
        {
            /* 居中显示 */
            Size size = Screen.PrimaryScreen.WorkingArea.Size;
            Left = (size.Width - Width) / 2;
            Top = (size.Height - Height) / 2;
            WindowState = FormWindowState.Normal;
            
            // this.StartPosition = FormStartPosition.CenterScreen;      //这一句加不加都行     
        }