ACTIONSCRIPT 3 Developer’s Guide en

Chapter 8: Handling events
Flash Player 9 and later, Adobe AIR 1.0 and later
An event-handling system allows programmers to respond to user input and system events in a convenient way. The
ActionScript 3.0 event model is not only convenient, but also standards-compliant, and well integrated with the
display list. Based on the Document Object Model (DOM) Level 3 Events Specification, an industry-standard eventhandling
architecture, the new event model provides a powerful yet intuitive event-handling tool for ActionScript
programmers.
The ActionScript 3.0 event-handling system interacts closely with the display list. To gain a basic understanding of the
display list, read “Display programming” on page 151.
More Help topics
flash.events package
Document Object Model (DOM) Level 3 Events Specification
Basics of handling events
Flash Player 9 and later, Adobe AIR 1.0 and later
You can think of events as occurrences of any kind in your SWF file that are of interest to you as a programmer. For
example, most SWF files support user interaction of some sort—whether it's something as simple as responding to a
mouse click or something more complex, such as accepting and processing data entered into a form. Any such user
interaction with your SWF file is considered an event. Events can also occur without any direct user interaction, such
as when data has finished loading from a server or when an attached camera has become active.
In ActionScript 3.0, each event is represented by an event object, which is an instance of the Event class or one of its
subclasses. An event object not only stores information about a specific event, but also contains methods that facilitate
manipulation of the event object. For example, when Flash Player or AIR detects a mouse click, it creates an event
object (an instance of the MouseEvent class) to represent that particular mouse click event.
After creating an event object, Flash Player or AIR dispatches it, which means that the event object is passed to the
object that is the target of the event. An object that serves as the destination for a dispatched event object is called an
event target. For example, when an attached camera becomes active, Flash Player dispatches an event object directly to
the event target, which in this case is the object that represents the camera. If the event target is on the display list,
however, the event object is passed down through the display list hierarchy until it reaches the event target. In some
cases, the event object then “bubbles” back up the display list hierarchy along the same route. This traversal of the
display list hierarchy is called the event flow.
You can “listen” for event objects in your code using event listeners. Event listeners are the functions or methods that
you write to respond to specific events. To ensure that your program responds to events, you must add event listeners
either to the event target or to any display list object that is part of an event object’s event flow.
Any time you write event listener code, it follows this basic structure (elements in bold are placeholders you’d fill in
for your specific case):
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