private void btnLoadGrid_Click(object sender, EventArgs e)
{
int ID_kho = Convert.ToInt32(ledKhoVT.EditValue);
int ID_loai_vat_tu = Convert.ToInt32(ledLoaiVT.EditValue);
gridView1.Columns.Clear();
gridTonKho.DataSource = Kho.TonKho(ID_kho, ID_loai_vat_tu);
gridView1.Columns[0].Width = 120;
}