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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Many internal ActionScript properties and methods describe the Flash movie envi-

ronment in Boolean terms. For example, if we ask, “Is the spacebar being pressed?”

the interpreter answers with a Boolean:

true (yes) or false (no):

// Key.isDown() is a function that returns either true or false

if (Key.isDown(Key.SPACE)) {

// Spacebar is being pressed, so make our spaceship fire

}

In Chapter 5, we’ll learn how to phrase complex logical expressions using Boolean

operators.

Using Boolean Values to Build a Preloader

Let’s consider an applied Boolean example. Suppose we have a document with 500

frames and lots of content. The beginning of our opening sequence, frame 20, is

labeled

intro. We put the following code on frame 2 of that movie’s main timeline:

if (this._framesloaded >= this._totalframes) {

this.gotoAndPlay("intro");

} else {

this.gotoAndPlay(1);

}

When the movie plays, the playhead passes frame 1 and enters frame 2. The Action-

Script interpreter reaches the conditional statement and evaluates the Boolean

expression within it: this._framesloaded >= this._totalframes. While the movie is still

loading,

this._framesloaded is less than the total number of frames in our movie

(

this._totalframes). If this._framesloaded is not greater than or equal to this.

_totalframes

, then the ...