private void cmb_MaSP_SelectedIndexChanged(object sender, EventArgs e)
{
txt_TenSP.Text = SP.TenSP(cmb_MaSP.SelectedValue.ToString());
txt_LoaiSP.Text = SP.LoaiSP(cmb_MaSP.SelectedValue.ToString());
txt_ThongTinSP.Text = SP.ThongTin(cmb_MaSP.SelectedValue.ToString());
txt_GiaBan.Text = SP.GiaBan(cmb_MaSP.SelectedValue.ToString());
txt_NCC.Text = SP.NhaCC(cmb_MaSP.SelectedValue.ToString());
txt_BaoHanh.Text = SP.BaoHanh(cmb_MaSP.SelectedValue.ToString());
}