private void BtnDelete_Click(object sender, EventArgs e)
{
DialogResult a = MessageBox.Show("Xóa NXB này!", "Thông báo!", MessageBoxButtons.OKCancel, MessageBoxIcon.Question);
if (a == DialogResult.OK)
{
db.XoaNXB(Convert.ToInt32(txtMaNXB.Text));
dgvNXB.DataSource = db.NXB_table();
}
}