private void cmdTinhThanh_Click(object sender, EventArgs e)
        {
            frmTinhThanh frm = new frmTinhThanh();

            frm.FormClosed += new FormClosedEventHandler(frm_FormClosed);
            frm.ShowDialog();
        }
 private void cmdTinhThanh_Click(object sender, EventArgs e)
 {
     frmTinhThanh frm = new frmTinhThanh();
     frm.FormClosed += new FormClosedEventHandler(frm_FormClosed);
     frm.ShowDialog();
 }