private void mnuXuLyMang_Click(object sender, EventArgs e)
        {
            frmXuLyMang frm = new frmXuLyMang();

            frm.MdiParent = this;
            frm.Show();
        }
        private void mnuXuLyMang_Click(object sender, EventArgs e)
        {
            frmXuLyMang frm = new frmXuLyMang();

            if (frm.ShowDialog() == DialogResult.OK)
            {
            }
        }