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.

Creating and Invoking the Subclass Constructor

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377

Creating and Invoking

the Subclass Constructor

For now, our Ball constructor (from Example 14-1) is defined on the main timeline

of our .fla file. Later, we’ll see how to move the constructor to our ballSymbol

Library symbol. The Ball constructor looks very much like the constructor functions

we saw in Chapter 12, with the added feature that it is defined in a global namespace

corresponding to the domain name,

moock.org (your classes should be defined in

your domain’s namespace, as in

com.yoursite.YourClass):

/*

* Ball Class Constructor.

*/

org.moock.Ball = function ( ) {

// Create Instance properties.

// ...

// Initialize instance.

// ...

};

However, you’ll notice that our class constructor does not define any parameters!

Remember that we’re creating a MovieClip subclass, and movie clip instances are not

created with the standard new Object() instantiation, which facilitates parameters.

Instead, movie clip instances are created with the functions attachMovie() or

duplicateMovieClip(), which generate the instance and invoke its class constructor (if

one is defined). Hence, to supply arguments to our Ball constructor function, we

have to pass them through either attachMovie() or duplicateMovieClip(). But we can’t

pass the arguments directly, ...