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.

Assigning the MovieClip Superclass

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// Attach movie call

var initObj = new Object( );

initObj.radius = 10;

initObj.velocity = {x:44, y:2};

initObj.ballColor = 0xFF0000;

initObj._x = 30;

initObj._y = 12;

this.attachMovie("ballSymbol", "redBall", 1, initObj);

While setting object properties directly on the initObj works, it poses two problems:

• Code is not properly centralized: the attachMovie() function takes on the respon-

sibility of creating instance properties, which should be the role of the construc-

tor function.

• Constructor parameters (which should be temporary) are left as permanent

properties of the new instance. The property

ballColor, for example, is no longer

needed after construction, yet it remains defined for as long as the instance

exists.

To centralize our code and ensure that our instance is not unnecessarily cluttered

with constructor-parameter properties, we define all our parameters on a single

params property of the initObject. When the constructor finishes executing, it then

deletes the

params property:

// Remove constructor params object from the instance.

delete this.params;

Assigning the MovieClip Superclass

We’ve created our Ball class constructor, and we have seen how to instantiate Ball

objects with attachMovie(). Now we have to make our Ball class a subclass ...