void Reload()
{
daoMH = new MonHocDAO();
//daoL = new LopDAO();
dataGridDanhSachMonHoc.ItemsSource = null;
//dataGridDanhSachLop.ItemsSource = null;
dataGridDanhSachMonHoc.ItemsSource = daoMH.GetMonHocs();
//dataGridDanhSachLop.ItemsSource = daoL.GetLops();
}