ADOBE® FLEX® 3: PROGRAMMING ACTIONSCRIPT™ 3.0

ADOBE FLEX 3

Developer Guide

232

If a user clicks on Child1 Node, Flash Player or AIR dispatches an event object into the event flow. As the following

image shows, the object’s journey starts at

Stage, moves down to Parent Node, then moves to Child1 Node, and

then “bubbles” back up to

Stage, moving through Parent Node again on its journey back to Stage.

In this example, the capture phase comprises

Stage and Parent Node during the initial downward journey. The

target phase comprises the time spent at

Child1 Node. The bubbling phase comprises Parent Node and Stage as

they are encountered during the upward journey back to the root node.

The event flow contributes to a more powerful event-handling system than that previously available to ActionScript

programmers. In previous versions of ActionScript, the event flow does not exist, which means that event listeners

can be added only to the object that generates the event. In ActionScript 3.0, you can add event listeners not only to

a target node, but also to any node along the event flow.

The ability to add event listeners along the event flow is useful when a user interface component comprises more

than one object. For example, a button object often contains a text object that serves as the button’s label. Without

the ability to add a listener to the event flow, you would have to add a listener to both the button object and the text

object to ensure that you receive notification about click events that occur anywhere on the button. The existence of

the event flow, however, allows you to place a single event listener on the button object that handles click events that

occur either on the text object or on the areas of the button object that are not obscured by the text object.

Not every event object, however, participates in all three phases of the event flow. Some types of events, such as the

enterFrame and init event types, are dispatched directly to the target node and participate in neither the capture

phase nor the bubbling phase. Other events may target objects that are not on the display list, such as events

dispatched to an instance of the Socket class. These event objects will also flow directly to the target object, without

participating in the capture and bubbling phases.

To find out how a particular event type behaves, you can either check the API documentation or examine the event

object's properties. Examining the event object’s properties is described in the following section.

Event objects

Event objects serve two main purposes in the new event-handling system. First, event objects represent actual events

by storing information about specific events in a set of properties. Second, event objects contain a set of methods

that allow you to manipulate event objects and affect the behavior of the event-handling system.

To facilitate access to these properties and methods, the Flash Player API defines an Event class that serves as the

base class for all event objects. The Event class defines a fundamental set of properties and methods that are common

to all event objects.

Stage

Parent Node

Child1 Node

Child2 Node

Capture

Phase

Bubbling

Phase

Target Phase