ActionScript for Flash MX: The Definitive Guide, Second Edition

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Chapter 12: Objects and Classes

Built-in Objects

Like built-in classes, built-in objects let us control the movie environment. The Key

object, for example, defines a series of properties and methods that tell us about the

state of a computer’s keyboard. To use these properties and methods, we don’t

instantiate a Key object, we simply use the Key object directly. Built-in objects are

made automatically by the interpreter when the Flash Player starts, and they are glo-

bally available throughout a movie.

Here, for example, we display the keycode of the currently depressed key by invok-

ing the Key object’s getCode( ) method:

trace(Key.getCode());

And here, we check whether the spacebar is depressed, using the isDown( ) method

and supplying the spacebar’s keycode as an argument:

trace(Key.isDown(Key.SPACE));

In the Language Reference, you’ll learn about the other built-in objects.

Learning the Ropes

Learning to write valid ActionScript code is only half the job of learning to program

in Flash. The other half comes with learning the available built-in classes and objects

and their many wonderful properties and methods. We’ll undertake that task in the

Language Reference. However, it’s not necessary to study all the classes and objects

in one sitting. Learn about movie clips to start, and ...