//show danh sach nguoi lien he
private void btnThemKhachHang_Click(object sender, EventArgs e)
{
frmKhachHangLienHe khachHang = new frmKhachHangLienHe();
khachHang.ShowDialog();
ThDSNguoiLienhe();
}
private void btnThemNguoiLienHe_Click(object sender, EventArgs e)
{
frmKhachHangLienHe thongtinKhachHang = new frmKhachHangLienHe();
thongtinKhachHang.ShowDialog();
}