private void btnThem_Click(object sender, EventArgs e)
{
//ThemPhong();
PHONG phong = new PHONG();
phong.Sophong = txtSP.Text;
phong.Sluongsv = Convert.ToInt32(cboSL.Text);
phong.LoaiPhong = cboLoaiPhong.Text;
PhongBLL.Add(phong);
ClearpanelDSPhong();
LoadPhong();
}