private void btnThem_Click(object sender, EventArgs e)
{
isInsert = true;
txtSDT.ResetText();
txtDiaChi.ResetText();
txtTenNV.ResetText();
txtLuong.ResetText();
txtTenNV.Focus();
grThongTinNhanVien.Enabled = true;
btnHuy.Enabled = true;
btnLuu.Enabled = true;
btnThem.Enabled = false;
btnSua.Enabled = false;
txtTenNV.Focus();
txtMaNV.Text = dbNhanVien.SetNewPrimaryKey();
}