how to I add a custom event handler to the a grid cell?
for some reason the below code is not working and i'm not sure why, or how do i create a custom event, i need to know when somebody expands the combobox or when the value changes ....

ComboBoxCell<String> comboBoxCell= new ComboBoxCell<String>(abc, new LabelProvider<String>() {
    public String getLabel(String item) {
        return item;

EventHandler handler = new ValueChangeHandler<String>() {    
    public void onValueChange( ValueChangeEvent<String> event ) {
        //TODO: implement

comboBoxCell.addHandler(handler, ValueChangeEvent.getType() );

Line 798: The method addHandler(H, GwtEvent.Type<H>) in the type AbstractEventInputCell<String,FieldCell.FieldViewData> is not applicable for the arguments (EventHandler, GwtEvent.Type<ValueChangeHandler<?>>)