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.

380

|

Chapter 14: Movie Clip Subclasses and Components

In plain English, this tells the interpreter, “when a ballSymbol instance is created,

invoke the org.moock.Ball() constructor, with the

this keyword pointing to the new

ballSymbol instance.”

The new MovieClip() statement only establishes a class as a subclass of

the MovieClip class (i.e., it merely establishes inheritance). It cannot be

used to create new movie clips for use in a movie! Use attachMovie(),

duplicateMovieClip(),orcreateEmptyMovieClip() to create new

instances of movie clips or movie clip subclasses, such as Ball.

For more information on Object.registerClass(), see the Language Reference.

Packaging Subclass Code and Library

Symbols Together

With our superclass assigned, we’ve created a fully functioning MovieClip subclass,

Ball. We can add methods and properties to it via

Ball.prototype, just as we would

with any class (as shown in Example 14-1). However, suppose we wanted to share

our Ball class with another developer. We might sensibly put our class in an external

.as file and tell the developer to

#include the file. But we’d also have to tell her to

make a Library symbol for the class and export that symbol as “

ballSymbol”. If the

developer doesn’t export the symbol, or if she exports it with the wrong linkage iden-

tifier, ...