// Logical attach.
getChildren().insert(child, beforeIndex);
GroupingHandlerRegistration g = ensureGroupingHandlerRegistration(child);
if (child instanceof HasShowHandlers) {
g.add(((HasShowHandlers) child).addShowHandler(new ShowHandler() {
@Override
public void onShow(ShowEvent event) {
onWidgetShow(event.getSource());
}
}));