Question

I have this code:

DOM.setEventListener(row.getElement(), new ClickListener(){

    @Override
    public void onClick(Widget sender) {
    // TODO Auto-generated method stub

    }});

I think the code is fine and ClickListener extends EventListener, but it gives error saying: The method setEventListener(Element, EventListener) in the type DOM is not applicable for the arguments (Element, new ClickListener(){})

Answer 1

The real answer is that you probably don’t. While this is available to attach listeners to events, you may only attach a single listener per element – that listen then gets all dom events that have been configured (see DOM.sinkEvents) – and you are responsible for making sure to detach all listeners before the page unloads, else some browsers will leak memory.

Instead, strongly consider using a Widget (and subclasses) to manage events. RootPanel, the base widget that others should be added to, will manage detaching all other widgets from the page to prevent memory leaks.

Additionally, you are able to listen to the events that happen within there based on the kind of event you are after. For example, even on a widget like a Label that doesnt’ normally fire mouseover events, you can still attach handlers and get notification:

Label label = new Label();
label.addDomHandler(new MouseOverHandler() {
  @Override
  public void onMouseOver(MouseOverEvent event) {
    // do something
  }
}, MouseOverEvent.getType());
RootPanel.get().add(label);

In most cases, you’ll be using existing support methods, like Button to get a click event – there are convinience methods already there for you, thanks to interfaces like HasClickHandlers:

Button button = new Button();
button.addClickHandler(new ClickHandler() {
  @Override
  public void onClick(ClickEvent event) {
    // do something
  }
});
panel.add(button);

More on GWT, Widget, and Memory leaks:

• https://developers.google.com/web-toolkit/articles/dom_events_memory_leaks_and_you
• http://code.google.com/p/google-web-toolkit/wiki/UnderstandingMemoryLeaks