GWT SelectBox ChangeHandler event doesn't work

Sample:

private Widget getSelectBox() {
  HorizontalPanel hPanel = new HorizontalPanel();
  hPanel.setSpacing(20);
  final ListBox dropBox = new ListBox(false);
  String[] listTypes = {"1", "2", "3"};
  for (int i = 0; i < listTypes.length; i++) {
    dropBox.addItem(listTypes[i]);
  }
  dropBox.ensureDebugId("cwListBox-dropBox");
  dropBox.getElement().setId("cms-dropBox");
  VerticalPanel dropBoxPanel = new VerticalPanel();
  dropBoxPanel.setSpacing(4);
  dropBoxPanel.add(dropBox);
  hPanel.add(dropBoxPanel);
  dropBox.addChangeHandler(new ChangeHandler() {
    public void onChange(ChangeEvent event) {
      Window.alert("change fired");
      dropBox.addItem("else");
      consoleLog("selected: "+ dropBox.getSelectedIndex());
    }
  });  
  return hPanel;
}

ChangeHandler isn't working. Although in the official example it works fine (http://samples.gwtproject.org/samples/Showcase/Showcase.html#!CwListBox ). But it isn't working in this code. There are no errors.

DOM.sinkEvents((com.google.gwt.user.client.Element) dropBox.getElement(), Event.ONCHANGE );
DOM.setEventListener((com.google.gwt.user.client.Element) dropBox.getElement(), new EventListener() {
    @Override
    public void onBrowserEvent(Event event) {
        if (DOM.eventGetType(event) == Event.ONCHANGE) {
              Window.alert("change fired");
              dropBox.addItem("who");
              consoleLog("selected: "+ dropBox.getSelectedIndex());                                        
        }                                             
    }
}); 

This way doesn't work neither.

upd: all works in MainEntryPoint class, but need panel.add(new SomeClass().getWidget()), and this isn't work

the reason for not working eventListener: inattention.

don't override html content of ready DOM like container.getElement().setInnerHTML(container.getElement().getInnerHTML()+"<div>somehtml</div>"); after adding any widget with a eventListener