User Guide

618 Chapter 6: Components Dictionary

The second usage example uses a dispatcher/listener event model. A component instance

(

pBarInstance) dispatches an event (in this case, progress) and the event is handled by a

function, also called a handler, on a listener object (

listenerObject) that you create. You define

a method with the same name as the event on the listener object; the method is called when the

event is triggered. When the event is triggered, it automatically passes an event object

(

eventObject) to the listener object method. Each event object has properties that contain

information about the event. You can use these properties to write code that handles the event.

Finally, you call the

EventDispatcher.addEventListener() method on the component

instance that broadcasts the event to register the listener with the instance. When the instance

dispatches the event, the listener is called.

For more information, see “EventDispatcher class” on page 415.

Example

This example creates a listener object, form, and defines a progress event handler on it. The

form listener is registered to the pBar instance in the last line of code. When the progress event

is triggered,

pBar broadcasts the event to the form listener, which calls the progress callback

function.

var form:Object = new Object();

form.progress = function(eventObj){

// eventObj.target is the component that generated the progress event,

// i.e., the progress bar.

trace("Current progress value = " + eventObj.target.value);

}

pBar.addEventListener("progress", form);