Dynamically Changing States | 311is sent to all subscribers via the Observer design pattern. Each of the windows show-
ing the results represents different languages understood by the combatants. When a
combatant is knocked out, it is automatically unsubscribed and no longer receives
information, even though it can sustain further hits recorded by the surviving com-
batants. (The Android is invulnerable, and so can keep firing and receiving informa-
tion even if all the others are knocked out.)
TheChangeHandlerclass is divided into several functions. The constructor function
instantiates the concrete subjects and concrete observers. Each of the observers is
given a name (nomDeGuerre) for keeping track of subscribers who are pushed into a
subscriber array (warrior). A second array (battleUpdate) stores the battle names for
each combatant placed in the text fields representing each combatant’s “damage infor-
mation center.” To simulate the different languages receiving the message from the
concrete subject, each combatant has a different font and border color for the text
field representing its information display. ThecreateTextWindow( ) andgetFont( )
functions handle the viewing objects.
All the objects in the Library panel are placed on the stage along with firing and dam-
age information in a rather large function,getParts( ). These visible objects are coor-
dinated with the instances of the concrete observers.
ThesetScore( )method can be invoked by instances of theConcreteSubjectclass.
Whenever, thesetScore( )method is called, the subscribing observers are notified
via thepassOn( )method, which returns the current score through theupdate( )
method. ThekillWarrior( )function invokes theunsubscribeObserver( )method so
that when a spaceship is knocked out of the game, it no longer receives messages.
Example 8-19 is a fairly large class, and you may want to break it down into smaller
classes or abstract some of the functions. However, it’s designed to show off the
ways in which the Observer design pattern can be used in a context where informa-
tion rapidly changes. Save the script asChangeHandler.asin the same folder as the
other files.
Example 8-19. ChangeHandler.as
package
{
import flash.events.Event;
import flash.events.MouseEvent;
import flash.text.TextField;
import flash.text.TextFormat;
import flash.display.Sprite;
public class ChangeHandler extends Sprite
{
private var eKiller:uint;
private var aKiller:uint;
private var aFlag:Number;
private var aeFlag:Number;