private void AsociarZona()
{
obra = cboObra.SelectedItem as Obra;
cboZona.DataSource = servicio.ComboListZonaByObra(obra.IdObra).Where(x => x.Estado == "Activo").ToList();
cboZona.DisplayMember = "Nombre";
zona = cboZona.SelectedItem as Zona;
}