ActionScript for Flash MX: The Definitive Guide, Second Edition

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Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

Listener Events

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If the code were attached to the ball movie clip itself, you could instead write:

delete this.onEnterFrame;

For a list of event handlers offered by a specific class or object, see the appropriate

entry in the Language Reference. In particular, be sure to study the Button and

MovieClip classes, which define the majority of user-interaction events. For exam-

ple, to cause a submitForm( ) function to execute when a Submit button is pressed,

we use:

submit_btn.onRelease = submitForm;

function submitForm ( ) {

// Validate data and send it to the server...

}

where submit_btn is the button object, the onRelease event is invoked when the but-

ton is pressed and then released, and submitForm( ) is a custom function that sends

the form data to the server. For a complete form-submission example, see

Chapter 17.

Event handlers are convenient, but they also suffer from a shortcoming: only one call-

back function can be registered (assigned) to an event handler at a time. That is, only

one action can be performed for each event when using event handler properties.

We’ll learn how to overcome this limitation in the next section using listener events.

Listener Events

Conceptually, listener events are similar to event handler properties. Like event han-

dler properties, listener events ...