ActionScript for Flash MX: The Definitive Guide, Second Edition

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Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

Classes and Object-Oriented Programming

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numbered array elements, with a for-in loop used to access an object’s properties.

For more information on for-in loops, including how to prevent an object’s proper-

ties from being exposed to for-in, see Chapter 8.

Object Methods

Methods are functions that are associated with objects and are typically used to per-

form an object-related task or access an object’s data (i.e., set and retrieve its proper-

ties). We invoke methods with the function call operator,

(), using the dot operator

to separate the method name from its object:

objectName.methodName()

For example:

ball.getArea( ); // Call the getArea( ) method of ball

As with properties, methods are defined by a class and then used with individual

object instances. For example, the MovieClip class defines a play( ) method that we

use on a particular movie clip instance (such as the main timeline of a movie):

_root.play( );

Methods can take parameters, return values, and otherwise behave exactly like

functions, with the added feature that they can access and operate on the object

through which they are invoked. For example, here we invoke gotoAndPlay( ) as a

method of the

_root movie clip object, passing the destination frame number, 5, as

an argument:

_root.gotoAndPlay(5);

And here we invoke the ...