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.

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Chapter 14

CHAPTER 14

Movie Clip Subclasses

and Components

In Chapter 12 we created a custom Ball class and used it to instantiate individual Ball

objects. When it came time to display the ball objects, we were faced with several

options. A separate Room class might contain balls and be responsible for drawing

them on screen with the Drawing API. Or, a Ball object might have a property,

mc,

that contains a movie clip used to represent the ball. In some cases, it’s redundant to

have one object that represents a thing (such as a ball) and a separate movie clip

object that displays it on screen. Movie clips, themselves, are already objects, so it

often makes sense to use a movie clip to both describe an object and display that

object on screen. In Flash MX, we can do so by creating a subclass based on the

MovieClip class, thus creating a specialized type of object that provides built-in

screen display.

In Flash 5, creating a MovieClip subclass involved an arduous series of

workarounds that proved impractical for most developers. Flash MX

introduces a formal MovieClip subclassing architecture that involves

the following new features:

#initclip, new MovieClip(), Object.

registerClass(), and attachMovie()’s

initObj parameter.

To see how MovieClip subclasses are created, we’ll implement our Ball ...