ActionScript for Flash MX: The Definitive Guide, Second Edition

This is the Title of the Book, eMatter Edition

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

Event Handler Scope

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which the button resides. When attached to a movie clip, an on( ) handler is scoped

to the clip that bears the handler, as with an onClipEvent( ) handler. Prior to Flash

MX, movie clips did not support on( ) handlers (only Flash 5 buttons did).

For example, if we place a button on the main timeline and declare the variable

speed

in a handler on that button, speed will be scoped to the main timeline ( _root):

// CODE FOR BUTTON HANDLER

on (release) {

var speed = 10; // Defines speed on _root

}

In contrast, if we place an on( ) handler on a movie clip object named ball and

declare the variable

speed in the handler, speed is scoped to ball:

// CODE FOR ball HANDLER

on (release) {

var speed = 10; // Defines speed on ball, not _root

}

Inside an on( ) handler for a button object, the this keyword refers to the timeline on

which the button resides:

// CODE FOR BUTTON HANDLER

on (release) {

// Make the clip on which this button resides 50% transparent

this._alpha = 50;

// Move the clip on which this button resides 10 pixels to the right

this._x += 10;

}

But inside a movie clip’s on( ) handler, the this keyword refers to the clip that bears

the handler:

// CODE FOR MOVIE CLIP HANDLER

on (release) {

// Make the clip with the handler 50% transparent

this._alpha = 50;

// Move the ...