How to detect new inserted line?

Hi, i have this code:


 public void addlinedirectly(Component source) {
       BigDecimal cero = BigDecimal.ZERO;

       PresupuestosLineas lineas = metadata.create(PresupuestosLineas.class);
       lineas.setDescripcion("");
       lineas.setCabecera(getItem());
       lineasDs.addItem(lineas);
       selectorarticulo.setValue(null);

}

After this line: selectorarticulo.setValue(null);

i need to call a Service to claculated amount in the table.
How can i send the correct LinesDS to the service class to make the working Service?

Now, i testet to send LinesDs.GetItem() but i received a null value.

Nothing, i passed " lineas " and worked fine!