Vb navigation via AppModel

AppModel.as

/**
 * Created with IntelliJ IDEA.
 * User: WouterDS
 * Date: 19/11/12
 * Time: 23:43
 * To change this template use File | Settings | File Templates.
 */
package be.wouterds.cubetester.model {
import flash.events.Event;
import flash.events.EventDispatcher;

public class AppModel extends EventDispatcher {
    /************************************
     * Properties
     ************************************/
    private static var instance:AppModel;

    private var _showNavigation:Boolean = false;
    private var _navigationAnimation:Boolean = false;

    public static const NAVIGATION_VISIBILITY_CHANGED:String = "navigationVisibilityChanged";

    /************************************
     * Methods
     ************************************/
    public static function getInstance():AppModel {
        if(instance == null) {
            trace("[AppModel.getInstance] Creating AppModel instance");
            instance = new AppModel(new Enforcer());
        }

        return instance;
    }

    public function AppModel(e:Enforcer):void {
        if(e == null)
            throw new Error("AppModel is a Singleton.");
    }

    /************************************
     * Handlers
     ************************************/

    /************************************
     * Getters & Setters
     ************************************/
    public function get showNavigation():Boolean {
        return _showNavigation;
    }

    public function set showNavigation(value:Boolean):void {
        if(_showNavigation !== value && !navigationAnimation) {
            _showNavigation = value;
            navigationAnimation = true;
            dispatchEvent(new Event(NAVIGATION_VISIBILITY_CHANGED));
        }
    }

    public function get navigationAnimation():Boolean {
        return _navigationAnimation;
    }

    public function set navigationAnimation(value:Boolean):void {
        if(_navigationAnimation !== value)
            _navigationAnimation = value;
    }
}
}

// Trick for Singletons in AS3
internal class Enforcer {};