Eclipse4/RCP/Modeled UI/Listening to Model Changes

When the model changes and it is not a no-op (for example, setting its label to its current label), an event will be dispatched to all interested event handlers. Eclipse 4 uses a global listener pattern so all handler subscriptions are done through the event broker.

Subscribing to model changes

Topics for event subscriptions can be generated from the UIEvents class.

// subscribe to all events generated from MUILabels
eventBroker.subscribe(UIEvents.buildTopic(UIEvents.UILabel.TOPIC),
    labelEventHandler);
 
// subscribe only to events generated from MItems's selected attribute being switched
eventBroker.subscribe(UIEvents.buildTopic(UIEvents.Item.TOPIC, UIEvents,Item.SELECTED),
    itemSelectionEventHandler);

Retrieving information from the events

// subscribe to events generated from MUILabels having their labels changed
eventBroker.subscribe(UIEvents.buildTopic(UIEvents.UILabel.TOPIC, UIEvents.UILabel.LABEL),
    new EventHandler() {
      public void handleEvent(Event event) {
        Object element = event.getProperty(UIEvents.EventTags.ELEMENT);
        if (element instanceof MToolItem) {
          ToolItem item = (ToolItem) ((MToolItem) element).getWidget();
          String value = (String) event.getProperty(UIEvents.EventTags.NEW_VALUE);
          if (value == null) {
            item.setText(""); //$NON-NLS-1$
          } else {
            item.setText(value);
          }
        }
      }
    }
);