#technical 2

[sharonjordan]

Before I begin the process of reworking the technical architecture, I am considering whether to build specifically for Android so that I could demonstrate my apps working on a device. This page - and other pages linking from it provide useful information about screen res and android build environment.

[sharonjordan]

A useful bank of information relating to modular application development.

I understand the principles of modular application development, but am not sure how best to plan out and document my modules.

[sharonjordan]

Singleton and Global Hooks

I have looked that the information about Singleton Design Patterns and subsequently at the GlobalHooks class Ian gave to me, with a little help from a Java-Programmer friend to explain how the Singleton works in principle.

From what I can gather, the GlobalHooks class that Ian has written, is basically a kind of wrapper. By adding the PagesDB to the GlobalHooks as a global property it enables me to then call the database via GlobalHooks, and ensures there is only one database.

However, in the current file structure it is not a true singleton because it doesn't prevent PagesDB from being called directly from elsewhere. If the PagesDB class was implemented as a Singleton, this would prevent it being called from anywhere else, and it could only ever exist as one instance.

I thought I would first try to implement the PagesDB as a Singleton, however, this led to numerous errors, one after another, some of which related to the current file structure and the fact that there is a circular reference between PagesDB and PagesXMLProcessor. It started to become very complex and so I reverted to using the GlobalHooks class as the singleton, and importing the database via the GlobalHooks class.

I added the following code to the main timeline in ebooks to make PagesDB a property of the GlobalHooks class.

//import the database as before to the main timeline var db:PagesDB = new PagesDB();

//get it to load data db.loadData(xmlMan.getRoot());

//store database in as property of GlobalHooks var sys:GlobalHooks = GlobalHooks.getInstance(); sys.addProp("pagesDatabase", db);

Then I added the following code into the pageviewer timeline to call the database stored in the global hooks instance:

var sys:GlobalHooks = GlobalHooks.getInstance(); var db:PagesDB = sys.getProp("pagesDatabase");

I also added a trace to make sure the correct database was loading.

Eureka....it worked!!

The only negative at the moment is that I removed other code so that the separate swfs don't work on their own because they need to reference the main timeline of the framework. However, I should be able to overcome this with an if statment to direct the db to load directly if it is being played outside the main timeline, but to load global hooks if played from within.

Next steps...modular application design framework, then begin construction all over again.

[sharonjordan]

This tutorial explains really well how to build and use a Singleton in ActionScript, with very easy to understand descriptions and sample code. It uses this basic structure for the class:

package{     public class Singleton{         private static var _instance:Singleton=null;         public function Singleton(){             trace(‘new instance of singleton created’);         }         public static function getInstance():Singleton{             if(_instance==null){                 _instance=new Singleton();             }             return _instance;         }     } }

This class controls that instantiation internally of whatever components are contained within the constructor function so that only one instance of the component ever exists, but there is public access to that single instance through the getInstance() method.

www.swinburne.edu.au/design/tutorials/P-flash/T-How-to-build-a-Singleton-in-Actionscript-3/ID-143/

[sharonjordan]

…the singleton pattern is a design pattern that is used to restrict instantiation of a class to one object… This is useful when exactly one object is needed to coordinate actions across the system.

www.swinburne.edu.au/design/tutorials/P-flash/T-How-to-build-a-Singleton-in-Actionscript-3/ID-143/

[sharonjordan]

Technical restructure needed

Earlier in the week I was having some issues with my script because the way it was structured was resulting in my database being created twice. In addition, I had also realised that I had approached the build 'backwards' - by starting at the application and then trying to add the framework around it - and that this was not going to work effectively to produce the full solution.

I need to restructure the technical architecture, starting with the portal and then loading all the assets into the framework. Ian suggested I plan this out by doing a modular application design to figure out where all the bits of functionality will sit.

Ian nalso suggested that I needed to start using more advanced application design techniques in order to centralise important application components, such as the database. The suggested I look at using a static class as part of a Singleton design pattern to do this, and then to use a GlobalHooks class that he had written to manage the process.

[sharonjordan]

Controlling sound between swfs

I have now added sound to the booksmenu swf and in order to be able to control the sound I have added a reference to the root swf (the one the menuswf is loaded into) by applying the following sample code from kb2.adobe.com/community/publishing/918/cpsid_91887.html

// create a variable to reference swf1's main timeline // this assumes that swf1 is a movieclip. var swf1Main_mc:MovieClip; // create your listener to ensure this loaded swf has been added //to the display list and can therefore obtain a reference to its //main timeline (which is always the main timeline of the loading swf). this.addEventListener(Event.ADDED_TO_STAGE, initF); function initF(e:Event):void{     swf1Main_mc = MovieClip(this.root); }

The sounds load within the books menu swf, but are played through the soundChannel loaded in the root swf. This enable me to also stop the sound when other events occur.

[sharonjordan]

This example is a pre-cursor to the record and save example, so I think would be worth looking at first to fully understand how it works.