private void btnAdd_Click(object sender, EventArgs e)
 {
     if (string.IsNullOrWhiteSpace(txtTenSP.Text) || string.IsNullOrWhiteSpace(txtDonVi.Text) || string.IsNullOrWhiteSpace(txtGiaBan.Text))
     {
         MessageBox.Show("Ban phai nhap day du thong tin");
         return;
     }
     else
     {
         flag = 1;
         product.AddProduct_Bus(getInfo(), dt);
         clear();
     }
 }