Form with combo and querycontainer

Hi,

I have a form with ComboBox, I 've loaded as this

mycombo.setContainerDataSource(app.storage.getPeopleQueryContainer());
mycombo.setItemCaptionPropertyId("fullname"); //app.storage.getPeopleQueryContainer() returns  id and fullname fields;


public Field createField(Item item, Object propertyId,
            Component uiContext) {
....
....
....
}

The question :

How to know the id when the user change combo value???

Thank you so much

Xavier

Use a ValueChangeListener on the ComboBox.