private void btKhachHang_Click(object sender, EventArgs e)
 {
     KhachHang kh = new KhachHang();
     kh.ShowDialog();
     khCtrl.HienThiComboBoxMaKhachHang(cmbMaKhachHang);
 }
 private void btKhachHang_Click(object sender, EventArgs e)
 {
     KhachHang kh = new KhachHang();
     kh.ShowDialog();
 }