GWT Custom Event Handler

Question

Can someone give me an example of creating a custom set of an Event and a Handler. Say you have a Person object that you want your widgets to know if it got updated.

Answer 1

Here's a pretty comprehensive example of creating a custom event, taken verbatim from the GwtEventSystem Wiki (when the event system was still in GWT's incubator).

This is an event that is triggered when the user becomes happy.

Define a new event class. You can add arbitrary metadata in the event class. For simplicity, we will not include any here though.

public class HappyEvent extends GwtEvent {
  ...
}

Define a new handler and marker interface for the event class.

interface HappyHandler extends EventHandler {
  public void onHappiness(HappyEvent event);
}

interface HasHappyEvents {
  public HandlerRegistration addHappyHandler(HappyHandler handler);
}

Add a unique event type

class HappyEvent extends AbstractEvent{
  public static AbstractEvent.Key KEY = new AbstractEvent.Key(){...}

  public GwtEvent.Key getKey(){
    return KEY; 
  }
  ...
}

Wire up the handler's fire method

class HappyEvent extends GwtEvent {
  static Key KEY = new Key(){
    protected void fire(HappyHandler handler, HappyEvent event) {
       handler.onHappiness(event);
    };
   ...
}