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.

Using Standalone Object Instances as Associative Arrays

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var obj = new Object( );

obj.x = 10;

obj.y = 20;

Assigning properties and methods to individual objects is, of course, bad OOP prac-

tice. But in ActionScript, it is also a completely legitimate way to store a group of

named values (much like a hash or associative array). In fact, many of ActionScript’s

built-in methods take generic objects as parameters. For example, MovieClip.

globalToLocal( ) takes a point object parameter that must supply an

x property and a

y property. The x and y properties represent a global position that will be converted

to a movie clip’s local coordinate system.

pt = new Object( ); // Create generic object to hold our point

pt.x = 0; // Left border of main Stage

pt.y = 0; // Top border of main Stage

this.globalToLocal(pt); // Convert pt to local coordinates

trace("From the current clip, the top-left corner of the main Stage is at ");

trace("x: " + pt.x + "y: " + pt.y);

Similarly, MovieClip.attachMovie( ) takes an initObj parameter used to transfer an

object’s properties to a new movie clip instance,

car_mc, as follows:

// Create an object

var initObj = new Object( );

// Create properties on the object

initObj.speed = 3;

initObj.onEnterFrame = function ( ) {

this._x += this.speed;

};

// Transfer the object's properties ...