Cross-Application Interactions in UcompOS Implementations

One of my primary goals in the design of the UcompOS Rich Productivity Framework was to create a flexible environment for the deployment of multiple Rich Internet Applications that needed to work either separately, or discretely to create a singular overall rich experience.

UcompOS Applications launched by the UcompOS Portal are sandboxed in such a way that they exist as isolated entities that can operate independently from the environment they’ve been loaded into.

As I touched upon in my posting on Building Drag and Drop Experiences in the UcompOS RPF, UcompOS applications should not attempt to access other UcompOS entities directly through direct ActionScript or JavaScript class/method interaction.

This is not to say that you cannot do this, but if you were going to, say, load two separate UcompOS entities into a n0n-sandboxed configuration, and have each entity access the other’s classes, you would obviously be tightly coupling the entities in such a way that if two different developers were working on each entity, one could very easily break the implementation unintentionally.

If you have a very compelling reason to do this, I have not prevented you from doing this.

In this posting, I will touch upon some of the numerous models for achieving cross-application interactivity in the UcompOS RPF.

Proxy Components and Services Dictionaries

The model for interactivity across the boundaries of UcompOS entities and applications is to use the framework that’s built into the UcompOS SDK, mainly Services Dictionaries and Proxy Components.  These are two extremely important concepts to understand, which is why I touch upon them so frequently.

In review, a Services Dictionary publishes a list of the “Public API” methods that an entity exposes to other entities.  A Proxy Component is a client apparatus in one entity that is built to connect to the Public API method sponsored by some other entity.

As I’ve also explained numerous times, and particularly in this posting, the UcompOS SDK has a number of Proxy Components built into it that are client apparatus’ to the Public API methods of the UcompOS Portal.  After all, the UcompOS Portal is simply one entity in the overall context of the UcompOS Continuum.

Numerous postings and tutorials I’ve posted give examples of building Services Dictionaries and Proxy Components so I won’t go into the details of this in this posting, but again, understanding their mechanics is crucial.

UcompOS SDK Events

Another crucial concept to understand in the UcompOS RPF is its Event-based implementation.

By strict convention, all Proxy Components extend a class in the UcompOS SDK named AbstractProxyComponent.

As the name implies, it is an abstract class and should never be instantiated directly, only extended.  (Unfortunately, ActionScript 3 doesn’t give us a true foolproof way to enforce abstractness.)

AbstractProxyComponent extends EventDispatcher so thus all Proxy Components inherit an addEventListener(); method.

So essentially, in one UcompOS entity, you can build a Proxy Component that talks to the Public API method in another entity.  And you can register an event listener to receive event notices from that Proxy Component.

That’s why I call these things “Proxy” Components.

You are creating a virtual representation in one entity of a physical implementation in another entity, so essentially, your Proxy Component is a “Proxy” to the true implementation that is actually located in an entirely different entity.

So when you do something like the following:

var w:UcompOSWindowProxy = new UcompOSWindowProxy();
w.add("http://blog.ucompass.com","UcompOS",800,600);
w.addEventListener(UcompOSWindowProxy.CLOSE,closeHandler);

w in the above scenario is an instance of the Proxy Component UcompOSWindowProxy that is built into the UcompOS SDK.

w is not REALLY the window that gets created on the UcompOS Portal, but it is a virtual representation of it.

But when you add an event listener on the CLOSE event of the window, it is as if you are attaching an event listener to the actual window itself.

I am hopeful that the concept of Proxy Components is making more and more sense to the dedicated readers of this blog.

The event handlers implemented with any Proxy Component are exclusively dispatched an instance of the SDKEvent class.

The SDKEvent class is worth studying.

If you look at the AS3 docs for the SDKEvent class, you’ll notice it has a collection of read-only properties.  One of which is data and another is proxyComponent.

By strict convention, any Public API method in a UcompOS entity returns an item of type Object.  This data is carried back to the Proxy Component that invoked the Public API Method in the form of an SDKEvent instance.

So for instance, building to our simple example above, I could do something like this:

w.addEventListener(UcompOSWindowProxy.WINDOW_INFO,windowInfoHandler);
w.getWindowInfo();
 
private function windowInfoHandler(event:SDKEvent):void
{
 
 // this will be the Object returned by the Public API method I contacted
 var data:Object = event.data;
 
 trace("Window size is "+data.width+" x "+data.height);
 
}

Let’s talk a bit about the proxyComponent property of SDKEvent instances.

It is of type IProxyComponent.

The AbstractProxyComponent event implements the interface IProxyComponent from the SDK, so any Proxy Component can be cast as an item of type IProxyComponent.

Dispatching an Event to a Proxy Component from a Public API Method

So you have built your Public API method and you have set up a Proxy Component in another entity to connect to this Public API Method.

As I have explained, the Object your Public API Method MUST return will be returned to your Proxy Component packaged in an SDKEvent instance.

But what if you asynchronously want to dispatch an SDKEvent to a Proxy Component?

The key to this is the BroadcastEvent class in the SDK and its static dispatchEvent(); method.

As an example of when we might use this capability, suppose we have a UcompOS AIR application that sponsors a Public API Method that allows us to asynchronously return the list of files in a directory.

The implementation of this might look something like this:

private var _uuid:String;
 
public function getFilesInDirectory(data:Object):Object
{
 _uuid = data._dataPackage.uuid;
 var directory:File = new File(data.directory);
 directory.addEventListener(FileListEvent.DIRECTORY_LISTING,getFilesInDirectory_handler);
 directory.getDirectoryListingAsync();
 return SDKEvent.VOID;
}
 
private function getFilesInDirectory_handler(event:FileListEvent):void
{
 var files:Array = [];
 for(var i:uint = 0;i<event.files.length;i++)
 {
 files.push((event.files[i] as File).name);
 }
 BroadcastEvent.dispatchEvent(_uuid,"fileListing",{files:files});    
}

As a brief aside, notice in the Public API method, I am returning SDKEvent.VOID.  This actually suppresses the return altogether of any data to the calling Proxy Component.  This is the best practice when your Public API method doesn’t return anything of value to the calling Proxy Component.

When the UcompOS SDK passes the input Object to a Public API method, it adds a property to the Object called _dataPackage which itself is an Object.

This Object has a property, uuid, which is the same value of the uuid property on the Proxy Component that originated the transaction with the Public API method.

The BroadcastEvent.dispatchEvent(); method expects this uuid value as the first input parameter.

A Proxy Component that invoked this Public API method could have an event listener listening for events of type “fileListing”.  In this scenario, the event handler would be dispatched an SDKEvent with the data dispatched to the BroadcastEvent.dispatchEvent(); method.

Dispatching Continuum Events

The UcompOSGlobalManagerProxy class in the UcompOS SDK has a method named dispatchContinuumEvent();.

It accepts two parameters – the type of event, and a data Object.

When you call this method, you are dispatching an event to every entity in the UcompOS Continuum and the event can be listened for on the UcompOSGlobalManagerProxy Singleton.

So for instance, you could say something like:

UcompOSGlobalManagerProxy.getInstance().dispatchContinuumEvent("myEvent",{name:Ed});

And in an entirely different entity, you could do something like this:

UcompOSGlobalManagerProxy.getInstance().addEventListener("myEvent",eventHandler);

and your event handler could look something like:

private function eventHandler(event:SDKEvent):void 
{
 
 trace("Your name is "+event.data.name);
 
}

The dispatchContinuumEvent(); method doesn’t need to target a specific entity as the BroadcastEvent.dispatchEvent(); method does – it simply dispatches an event to EVERY entity.

Launching one UcompOS Application from Another Entity

The UcompOSGlobalManagerProxy class has a launchApplication(); method which accepts as input an Application Manifest URL as a String.

This enables you to launch a UcompOS Application from another entity.  Similarly, there is a quitApplication(); method as well as a getConnectionId(); method which can be used to find the connectionId of an already running UcompOS Application.

UcompOS Shared Objects

As I posted here, the UcompOS RPF now has a Shared Object implementation where an entity can house Objects of specific names on an Object on the UcompOS Portal that is available to all other entities.

When any Shared Object is created or its properties are updated, a Continuum Event is dispatched.

This creates an environment where the Shared Object itself can become a useful medium for achieving inter-application and inter-entity communication.

The UcompOS Event Propagation Model

The other day, I wrote a blog posting describing how the UcompOS RPF implements the MVC design pattern.

This implies that there is an event-driven architecture that has been facilitated in the UcompOS Continuum and that is indeed the case.

In this blog posting, we have to roll our sleeves up and really dig into the UcompOS SDK so that I can help you understand how the UcompOS RPF Event Architecture works.  If you have full command of the UcompOS RPF’s event architecture, it will help you build the most engaging and interactive rich experiences for your Rich Portal Applications.

The architecture at first glance is necessarily complex and involved and this will probably likely be just one of many blog postings I’ll make in reference to this topic and as time passes, I am going to work hard to make the event architecture simpler, more transparent, and as close as possible to best practice.  Of course developer feedback will be a crucial part of that mission.

CommandObject Transactions

If you’ve read my other postings, you have a very basic understanding of Proxy Components and Services Dictionaries.

Simply put, a UcompOS entity exposes its internal functionality to other UcompOS entities by publishing a Services Dictionary and a UcompOS entity contacts functionality in another entity by using a Proxy Component.

By strict convention, ALL communication between entities in the UcompOS Continuum should occur via the SDK class SDKClient and its send(); method.  (NOTE: There is a very esoteric exception to this that is handled behind the scenes by the UcompOS RPF that would involve two UcompOS entities participating in drag and drop interactions but that is beyond the scope of my article here and will be covered in an upcoming tutorial.)

The UcompOS SDK has both client and server infrastructure implemented.  Therefore, each UcompOS entity is capable of serving both as a server capable of receiving commands from other entities as well as a client capable of sending commands to other entities simultaneously.

The UcompOS RPF implements an asynchronous event dispatchment model.

When an entity needs to access a public API command in another entity, it (usually with the assistance of a Proxy Component) creates a CommandObject instance that is packaged into a DataPackage instance and sends it to the target entity via the SDKClient send(); method.  All these details are masked by the call(); method of AbstractProxyComponent which all Proxy Components must inherit from.

The server(); method of the SDKServer class is the first spot in the target entity to come in contact with the DataPackage.

DataPackages sent across the SDK Tunnel are encoded into compressed ByteArrays.

The server implementation in the SDK decodes the DataPackage and passes it to one of a couple different polymorphic constructs in the SDK:  CommandObjectHandler or EventObjectHandler

In the scenario where one entity is contacting the public API method of another entity, the DataPackage will contain a CommandObject and thus the DataPackage will be passed to the CommandObjectHandler in the SDK.

This will pass the data Object to the internal implementation code in the target entity.

By strict convention, any method that is capable of being targeted by another entity must accept exactly one parameter of type Object and return an item of type Object.

In order to understand the full event cycle in the UcompOS RPF, we must study what happens when this public API method returns this Object.  Where does this Object go from here?  How does it get back to the calling entity?

CommandObjectHandler passed the DataPackage to the internal implementation method and is returned the Object return from the method.

At this point, CommandObjectHandler turns from a server implementation to a client implementation and it creates a new DataPackage, puts an EventObject instance into it, and then sends the DataPackage back to the original entity.  So the original entity then becomes a server.

When the DataPackage with the EventObject packaged into it gets back to the SDKServer implementation in the calling entity, it is passed to the EventObjectHandler class.

The EventObjectHandler class then passes it to any event handlers that have been attached to the Proxy Component that made the initial public API call in the first place.

This is in fact why AbstractProxyComponent, which all Proxy Components extend from, inherits from EventDispatcher – so we can implement addEventListener(); thus implementing a paradigm many Flex and Flash coders are much more accustomed to.

When a public API method returns its required Object, an eventType property can be set to it.  If you do not explicitly set this, then CommandObjectHandler will set this for you as the constant SDKEvent.COMPLETE.

This eventType property is important as it has implications as far as how events get passed to a Proxy Component’s event handlers.

Suppose I have the following Services Dictionary class in a UcompOS application:

package
{
 
  import com.ucompass.ucompos.sdk.server.AbstractServicesDictionary;
 
  public class ServicesDictionary extends AbstractServicesDictionary
  {
    _map =
    {
      'Greeting.sayHello':
      {
 
        static:true,
        classRef:api,
        method:'sayHello',
        description:'Returns a greeting'
      }
 
    };
 
  }
 
}

Let’s suppose I have the following public API method that maps to Greeting.sayHello in my Services Dictionary example above:

public static function sayHello(data:Object):Object
{
  return {eventType:"Hello",greeting:"Hello there, "+data.name+"!"};
}

Now let’s suppose my Proxy Component located in another entity that will contact the Greeting.sayHello method above looks something like this:

package
{
 
  import com.ucompass.ucompos.sdk.client.AbstractProxyComponent;
  import com.ucompass.ucompos.sdk.model.SDKModel;
 
  public class Greeting extends AbstractProxyComponent
  {
 
    public function Greeting()
    {
      super._destination = SDKModel.getInstance().parent;
    }
 
    public function getGreeting(name:String):void
    {
      call("Greeting.sayHello",{name:name});
    }
 
  }
 
}
}

In my entity that will call Greeting.sayHello, I may see the following:

var g:Greeting = new Greeting();
g.getGreeting("Edward");

Now how do I get the greeting back from the entity that is exposing the public API method Greeting.sayHello?

Because AbstractProxyComponent extends EventDispatcher, and because my Greeting Proxy Component extends AbstractProxyComponent (a strict requirement of all Proxy Components), I can add an event listener to it.

g.addEventListener("Hello",greetingHandler);
 
private function greetingHandler(event:SDKEvent):void
{
  var greeting:String = event.data.greeting;
}

Notice my event handler is passed an instance of SDKEvent.  This is universal for all Proxy Components.

The SDKEvent instance will have a data property which will be the data Object returned by the remote public API method in the contacted entity.

Therefore, the eventType property in the return Object of a public API method determines which Proxy Component event handlers are passed an SDKEvent instance.

UcompOS Continuum Events

The above example shows a very simple example of an asynchronous request-response phase of a Proxy Component – public API method transaction.

There is another type of event in the UcompOS RPF called a Continuum Event.

The UcompOS Portal sponsors a public API method named GlobalManager.dispatchEvent.  This is accessed through the UcompOSGlobalManagerProxy Singleton class in the UcompOS SDK and its dispatchContinuumEvent(); method which accepts as input two parameters: type:String, and data:Object

When this method is accessed, every entity in the entire UcompOS Continuum is dispatched the event.

The implications of this is that you can monitor activity across the boundaries of different applications.  For instance, maybe you have a UcompOS Chat Application and when you receive an instant message from an individual user, you automatically want a separate UcompOS Address Book Application to open to that user’s Address Book entry.

Targeted EventObject Instances

The BroadcastEvent Singleton class in the UcompOS SDK has a dispatchEvent(); method.  This lets you send an EventObject on the fly to a single target entity.

For instance, the UcompOS SDK has a Proxy Component, that is the interface to various public API methods in the UcompOS Portal, called UcompOSWindowProxy.  The UcompOSWindowProxy‘s add(); method attaches an MDI window to the UcompOS Portal.

Internal to the UcompOS Portal implementation, it wants to notify the entity that created the UcompOS Window instance when certain user-driven activities occur such as when the window is moved, closed, minimized, maximized, etc.

Let’s look at a very simple example with some code.

Let’s suppose I have a UcompOS Application and I want to create a UcompOS Window, then I want to know when the user has closed the window.

In my application, the code I’d use to form the UcompOS Window could look like this:

var w:UcompOSWindowProxy = new UcompOSWindowProxy();
w.add("http://desktop.ucompass.com/MySubApp.swf","My Sub Application",500,500,100,100);

This will load the content at http://desktop.ucompass.com/MySubApp.swf into a UcompOS Window of dimensions 500 x 500 positioned at (100,100) from the upper-left origin point of the UcompOS Portal.

Now suppose I want to know when that window has closed.

No problem:

w.addEventListener(UcompOSWindowProxy.CLOSE,closeHandler);
private function closeHandler(event:SDKEvent):void
{
 // the window has closed
}

The reason why this works this way is that internal to the UcompOS Portal, there is a call to the UcompOS SDK static method BroadcastEvent.dispatchEvent(); that dispatches an EventObject (encapsulated in a DataPackage of course) to the entity that created the UcompOS Window.

As another example, consider the UcompOSMenuBarProxy class.  I haven’t covered the UcompOS Menu Bar in any tutorials quite yet, but the UcompOSMenuBarProxy class has a setMenuBar(); method that lets you attach an XML model that will be used as the dataProvider for the Menu Bar on the UcompOS Portal while the application in scope is in focus.

You could do something like this:

var menuModel:XML = new XML("<menu><menuitem label='File'><menuitem label='Open' data='1'/><menuitem label='Close' data='2'/></menuitem></menu>");
var m:UcompOSMenuBarProxy = UcompOSMenuBarProxy.getInstance();
m.setMenuBar(menuModel);
m.addEventListener(UcompOSMenuBarProxy.CHANGE,menuBarHandler);
 
private function menuBarHandler(event:SDKEvent):void
{
 var chooseString:String = "User chose "+event.data.label+" whose data property is "+event.data.data;
}

Summary

The event architecture in the UcompOS RPF is indeed complex at first glance.  There is no getting around that.  I am going to continue to work to simplify it, improve the documentation surrounding it, and get the implementation details as close as possible to a true best practice MVC implementation.

A Simple HTML Digital Camera Browser

In this tutorial, we will look at a variety of core UcompOS Rich Productivity Framework concepts, and in particular we will explore the mechanics of adding a desktop component to your UcompOS Rich Portal Application.

It is recommended you download the source of the application we’ll build in this tutorial at the link below so you can follow along and there is also a video demonstration of the application we are going to build in this tutorial.

Download the Simple HTML Digital Camera Browser Source Code

This tutorial assumes you have at least a basic working knowledge of:

  • Adobe AIR 2.0
  • Adobe Flash Builder
  • ActionScript 3.0
  • HTML
  • JavaScript
  • You should have read my blog posts or watched my video tutorials about UcompOS Proxy Components and Services Dictionaries

The goals for our application are as follows:

We want to build a simple digital camera browser that lets the user browse through and view images from their digital camera in a Rich Portal Application implementation.

We are going to keep the application as deliberately simple as possible and we are not going to address its cosmetics or aesthetics so that we can focus on providing instruction on specific UcompOS concepts and principles.

To further define the specifications for our application, we want to build a UcompOS Application that prompts the user to connect their digital camera to their computer.  We want our application to be able to know when their digital camera has been connected.  Then when the digital camera has been connected, we want to display the contents of their camera to them.  The user should be able to easily browse through their camera’s contents and they should be able to click on a file on the camera to view it.  Also, the file should be opened in the native photo-viewing application on their computer versus simply displayed in the browser.

Again, we are going to focus on a very simple implementation and will not focus on aesthetics or presentation so that we can focus more on the core UcompOS mechanics we are leveraging to build our application.

Our UcompOS application is comprised of the following components:

  • An AIR 2.0 UcompOS Application built with Adobe Flash Builder 4
  • An HTML UcompOS Sub Application

We’ll walk through the process of setting up and building the different pieces of the application fairly linearly and then tie it all together at the end with a screenshot of our application.

Implementation Details

The way I want to design our program, I want a UcompOS Application to load on the UcompOS Application Dock entitled “My Camera”.  When this application is opened, we want it to launch our UcompOS AIR 2.0 application.  I want that application to prompt the user to connect their digital camera.

When the user connects their digital camera, I want to instantly launch a UcompOS Window instance in the UcompOS Portal that displays the contents of the camera to the end user and allows them to browse through any folder structures housed on the camera and then I want to allow them to select a file to be viewed in their default photo viewing application on their computer.

When the camera is disconnected, I want to shut down the application.

Setting up the AIR 2.0 Application

While I could use a number of different technologies to build our AIR application, I am going to use Adobe Flash Builder 4.   The minimum required version for a UcompOS AIR application is AIR 2.0.  You can learn more about AIR 2.0 and access its run-time and SDK at http://labs.adobe.com/technologies/air2/.

The first step is to set up a Flash Builder project for my AIR application.

My project is called Camera_Example.  Pictured at left is the fully expanded project in Flash Builder with all its files. flash_builder_project

Our main class in our AIR application is Camera_Example.mxml.

Notice in my libs folder is the file UcompOSAIRSDK.swc.  This is the UcompOS SDK file for AIR applications.  This file is found in the UcompOS Developers Package in the sdk/air folder that is created when you unzip the UcompOSSDK.zip file contained in the package.

Simply drag and drop that file into the libs folder of any Flash Builder (or Flex) based UcompOS AIR application.

You can also incorporate the UcompOS AIR SDK into Flash-based and HTML-based AIR applications (the SDK has no Flex dependencies) but the techniques for doing so are outside the scope of this tutorial.

Ideally, my goal is for the end user to not even have any knowledge that an AIR application is involved other than the initial install process.  I want the user to operate entirely within the web browser here and my rationale for this in this tutorial is with the goal in mind of showing how multiple technologies are fusing together to create a seamless rich experience.

Of course, AIR needs to be involved because AIR is what we use to do most of the heavy lifting in our application including detecting the camera attachment/detachment, browsing through the camera’s contents, and opening individual pictures on the desktop.

From an implementation point of view, an AIR application can only be launched from the web browser following a user-initiated event such as a mouse click.

When an AIR application is configured as the base source code for a UcompOS Application, and this application appears on the UcompOS Application Dock, when the user clicks the icon in the application dock, that user event is what triggers the launching of the AIR application.

I’ll add that it is possible to implement UcompOS AIR sub-applications and the best practice for doing this is to leverage the UcompOSArtifactProxy class.  This topic will be covered in a future tutorial in the near future.

Our AIR Application’s Descriptor File

Our Camera_Example-app.xml file needs a very crucial adjustment.

By default, you’ll see this XML element commented out:

<!-- <allowBrowserInvocation></allowBrowserInvocation> -->

This needs to be uncommented and issued a true value:

<allowBrowserInvocation>true</allowBrowserInvocation>

This tells the AIR runtime that your application is allowed to be launched from the web browser.

If you try to instantiate the UcompOS AIR SDK in an AIR application that does not have its descriptor set up in this manner, you’ll get a compile-time error and you won’t be able to package your application.

cameraEven though we do want our AIR application to be as innocuous as possible, if a user does stumble upon it on their main OS’ dock or in the folder on their computer where it’s been installed, I want them to see the custom icon at left and this icon and other varieties in different sizes are in the assets_embed/png folder.

Therefore in my app-descriptor file, I have implemented the following:

<icon>
 <image16x16>assets_embed/png/image16x16.png</image16x16>
 <image32x32>assets_embed/png/image32x32.png</image32x32>
 <image48x48>assets_embed/png/image48x48.png</image48x48>
 <image128x128>assets_embed/png/image128x128.png</image128x128>
 </icon>

AIR Application Code

Since I want the user to know as little as possible, if anything, about the presence of the AIR application, I want it to be invisible.  Therefore, I’ll give the visible property in the root WindowedApplication tag a value of false.  This will suppress any windows from being displayed.

Next, I want to instantiate the UcompOS SDK.

This should happen once the main application dispatches its applicationComplete event.

My root MXML tag looks like this:

<s:WindowedApplication xmlns:fx="http://ns.adobe.com/mxml/2009"
   xmlns:s="library://ns.adobe.com/flex/spark"
   xmlns:mx="library://ns.adobe.com/flex/halo"
   applicationComplete="start();"
 visible="false">

Now let’s take a look at the private variables I am declaring in my main class.  We’ll cover the purpose of each of these variables further in the tutorial:

private static var _cameraRoot:String;
private var _h:UcompOSHTMLProxy;
private var _d:UcompOSDockProxy;

Now let’s take a look at my start(); method:

private function start():void
{
 AIRSDKClient.getInstance(this,new ServicesDictionary());
 AIRSDKClient.getInstance().addEventListener(SDKClient.SDK_READY,ucompos_init);
 implementStorageVolumeListeners();
}

The instantiation of the UcompOS AIR SDK is very similar to the instantiation of the UcompOS Flex/Flash SDK that targets browser-based content with a few key exceptions:

  • The Singleton class AIRSDKClient is leveraged versus the SDKClient class
  • We pass this as the first parameter to the getInstance(); method and an optional Services Dictionary as the second parameter.  We’ll look at the Services Dictionary for this application below.
  • Internal to the AIRSDKClient class, the SDKClient class is instantiated.  Once it is instantiated, it dispatches an Event of type SDKClient.SDK_READY and only then can you safely instantiate and use any of the Proxy Components built into the SDK so you must listen for this event and implement any Proxy Component-related startup code in the event handler for this event

In our start(); method, we have a call to implementStorageVolumeListeners();

Let’s take a look at the implementStorageVolumeListeners(); method:

private function implementStorageVolumeListeners():void
{
 StorageVolumeInfo.storageVolumeInfo.addEventListener(StorageVolumeChangeEvent.STORAGE_VOLUME_MOUNT,mountHandler);
 StorageVolumeInfo.storageVolumeInfo.addEventListener(StorageVolumeChangeEvent.STORAGE_VOLUME_UNMOUNT,unmountHandler);
}

This method leverages AIR 2.0 capabilities.  StorageVolumeInfo is a Singleton class in AIR 2.0 that can have an event listener attached to it to handle StorageVolumeChangeEvent.STORAGE_VOLUME_MOUNT and StorageVolumeChangeEvent.STORAGE_VOLUME_UNMOUNT events.  These events are dispatched whenever a new mount point is introduced to the base Operating System or whenever a mount point is removed.  Our handlers for these events are mountHandler(); and unmountHandler(); respectively.

Before we take a look at mountHandler(); and unmountHandler();, let’s take a look at the ucompos_init(); method that is invoked once our UcompOS AIR SDK has been fully initialized and we are ready to interact with it fully:

private function ucompos_init(event:Event):void
 {
  _h = new UcompOSHTMLProxy();
  _h.alert("Please connect your digital camera to your computer");
  _d = UcompOSDockProxy.getInstance();
 }

In this method, we are creating an instance of UcompOSHTMLProxy.  This class has a number of methods that let us execute common JavaScript methods such as alert();, prompt();, and confirm(); in the UcompOS Portal’s HTML wrapper file.

I am choosing to use a regular JavaScript alert to prompt the user to connect their digital camera to their computer.

I am also going to create a reference to the UcompOSDockProxy Singleton and my reasons for doing this will become clear below.

Now, let’s take a look at the mountHandler(); method.

private function mountHandler(event:StorageVolumeChangeEvent):void
{
 _d.setAlert(true);
 _cameraRoot = event.rootDirectory.nativePath;
 w = new UcompOSWindowProxy();
 w.add("http://desktop.ucompass.com/Camera_Example/Camera_Browser.html",event.rootDirectory.name,400,400);
 var object:Object = API.getFiles({});
 }

This method is invoked when the user attaches a new storage volume to their computer.  It is worth mentioning at this time that the simple example being developed here could be used to browse any type of removable storage.  We just happen to be focusing on a scenario that would involve a digital camera.

The implementation details of mountHandler(); are straightforward.  First, we want to call the setAlert(); method of the UcompOSDockProxy instance and pass a value of true to it.  This makes the icon associated with this application on the UcompOS Portal Application Dock “Chirp” and glow drawing the user’s attention to it.

Then, we want to set the _cameraRoot property to event.rootDirectory.nativePath.  The StorageVolumeChangeEvent contains a rootDirectory property which is of type File and represents the file location on the file system where the base of the mount point is located.

Next we create an instance of UcompOSWindowProxy of 400 x 400 and load our HTML sub-application into it.  Our HTML sub-application will be the actual camera browser that the end user interacts with and we’ll review that later.

Our unmountHandler(); method is extremely simple:

private function unmountHandler(event:StorageVolumeChangeEvent):void
{
 w.close();
 UcompOSGlobalManagerProxy.getInstance().quitApplication();
}

This calls the close(); method on our UcompOSWindowProxy instance and then quits out of the application once the camera is removed.

Way back when we instantiated the UcompOS AIR SDK, we passed a new instance of ServicesDictionary to the instantiation method.

There are two public API methods we need our AIR application to sponsor and we are calling them Camera.getFiles and Camera.openFile.

Camera.getFiles will take the path to a given folder on the file system and return a list of the contents of that folder.

Camera.openFile will take the path to a given file on the file system and open it up with the application on the computer that the file is associated with.

First, let’s take a look at our ServicesDictionary:

package cameraexample
{
  import com.ucompass.ucompos.sdk.server.AbstractServicesDictionary;
  public class ServicesDictionary extends AbstractServicesDictionary
  {
    public function ServicesDictionary()
    {
      _map =
      {
        'Camera.getFiles':
        {
          static:true,
          classRef:API,
          method:'getFiles',
          description:'Lists files in a folder'
        },
 
        'Camera.openFile':
        {
          static:true,
          classRef:API,
          method:'openFile',
          description:'Opens a file in its native application'
        }
      }
    }
  }
}

As you can see, both of our public API methods are housed as static methods in an API class.

Here is the method that corresponds to the Camera.getFiles public API method:

public static function getFiles(data:Object):Object
{
  var folder:String = data.folder;
  if(!folder)
  {
    folder = Camera_Example.cameraRoot;
  }
 
  var file:File = new File(folder);
  var files:Array = [];
 
  for(var i:uint = 0;i<file.getDirectoryListing().length;i++)
  {
    var _file:File = file.getDirectoryListing()[i] as File;
    files.push({name:_file.name,isDirectory:_file.isDirectory});
  }
 
  return {eventType:"files",files:files,folder:folder};
 
}

The Camera.getFiles public API method expects a folder property to be on the Object parameter passed to the method.  If it’s not, it retrieves the contents at the base of the camera.

Back in our base application, we have a static getter function that retrieves the value of cameraRoot (which is why we established the value of _cameraRoot in the mountHandler(); method).

Our method simply builds an Array of Objects each having a name property and a Boolean to indicate if the item is a directory.

In our return Object, we return the eventType property set to files as well as our Array of files and a reference to the folder whose contents were retrieved.  We’ll learn more about the purpose of this eventType property when we look at our HTML sub-application.

Our public API method Camera.openFile is extremely simple:

public static function openFile(data:Object):Object
{
 var file:File = new File(data.file);
 file.openWithDefaultApplication();
 return {};
}

That’s it for our AIR application.  We are ready to package it with adt or the compiler built into Flash Builder.

I am packaging it into a file named Camera_Example.air and it will be reachable at a network URL of http://desktop.ucompass.com/Camera_Example/Camera_Example.air

Our HTML Sub-Application

Now we are ready to build our HTML sub-application which will be the interface the end-user actually interacts with.

The URL of our application will be at http://desktop.ucompass.com/Camera_Example/Camera_Browser.html.  This is the URL passed to the add(); method of our UcompOSWindowProxy instance of our mountHandler(); method in our AIR application.

We want this application to be extremely simple.

We just want it to list out the contents of our digital camera and present them as files or folders.

When the user clicks on a folder resource, we want to display the items in that folder.  When they click on a file resource, we want to open that file in the application that the file is associated with on their computer.

From an implementation point of view, when we click a folder, we are going to call our AIR application’s public API method Camera.getFiles and when we click a file we are going to call Camera.openFile.

The first thing we are going to do in our HTML sub-application is implement the UcompOS JavaScript SDK:

<script type="text/javascript" src="/UcompOSSDK.js"></script>

While it is not a requirement, best practice recommends you place the UcompOS JavaScript SDK and SWF files in the root directory of your webserver.

Here are two variables we initialize:

var camera;
var d;

When the UcompOS JavaScript SDK has initialized, it looks for a start(); method in the application its implemented into.

Our start(); method is as follows:

function start()
 {
   d = new UcompOSDockProxy();
   camera = new Camera();
   camera.addEventListener("files",filesHandler);
   camera.getFiles();
 }

We are creating an instance of UcompOSDockProxy which we’ll use to suspend the Dock alert we set in our AIR application.

More importantly, we are creating an instance of Camera, and adding an event listener to it and calling its getFiles(); method.

Camera is a Proxy Component we have built in our HTML sub-application.  A Proxy Component is an interface to the public API methods located in other entities.

In our case, the Proxy Component Camera in our sub-application is the interface to the Camera.getFiles and Camera.openFile public API methods sponsored by our AIR application.

Let’s take a look at our Proxy Component Camera and walk through it as the mechanics of Proxy Components are very important to understand:

function Camera()
{
  this.setDestination(parentConnectionId);
  this.getFiles = function(folder)
  {
    this.call("Camera.getFiles",{folder:folder});
  }
 
  this.openFile = function(file)
  {
    this.call("Camera.openFile",{file:file});
  }
}
 
Camera.prototype = new AbstractProxyComponent();
Camera.prototype.constructor = Camera;

The last two lines of the class would be analogous to saying Camera extends AbstractProxyComponent in ActionScript 3.0.  Any Proxy Component must extend AbstractProxyComponent (in ActionScript as well as JavaScript).

In our class implementation, we pass the parentConnectionId property to the setDestination method of our class (which is a method inherited from AbstractProxyComponent).

Since our sub-application was launched by our AIR application, in the context of the UcompOS Continuum, we know that our AIR application is the parent of the sub-application in scope and we can safely use the UcompOS JavaScript SDK global variable parentConnectionId (this is analogous to the public property SDKModel.getInstance().parent in the UcompOS AIR/Flash/Flex SDK).

Our Camera class also implements two methods: getFiles(); and openFile();.  As you can see by referring to the class code, both of these call the public API methods in our AIR application Camera.getFiles and Camera.openFile by using the call(); method in our class that is inherited from AbstractProxyComponent.

Another very important point, in our start(); method, refer again to this command:

camera.addEventListener("files",filesHandler);

This tells our instance of our Camera class to pass any SDKEvent’s of type “files” to the method filesHandler.

If you refer to our AIR application public API method Camera.getFiles, you’ll recall its return Object sets an eventType property to “files“.

The return Object of the public API method Camera.getFiles is passed to our filesHandler(); method.

Here is the code of our filesHandler(); method:

function filesHandler(data)
{
  var e = document.getElementById('files');
  e.innerHTML = '<p><a href="javascript:void(0);" onclick="getFiles();">Camera Root</a><p/><hr/><p/><u>Current folder: '+data.folder+'</u>';
  for(var i = 0;i<data.files.length;i++)
  {
    if(data.files[i].isDirectory)
    {
      e.innerHTML+='<p/><img src="icons/folder.gif"/> <a href="javascript:void(0);" onclick="getFiles(\''+data.folder+'/'+data.files[i].name+'\');">'+data.files[i].name+'</a>';
    }
    else
    {
      e.innerHTML+='<p/><img src="icons/file.gif"/> <a href="javascript:void(0);" onclick="openFile(\''+data.folder+'/'+data.files[i].name+'\');">'+data.files[i].name+'</a>';
    }
  }
}

Notice we are referencing the files and folder properties of the Object passed to filesHandler();.  We iterate on the files property which we know from our inspection of our AIR application’s public API method Camera.getFiles is an Array and we further know that each Object in this Array has a name:String and isDirectory:Boolean property.

We create simple HTML that displays the name of the files and folders with the appropriate icons and calls the methods getFiles(); for folders and openFile(); for files.

These methods appear below:

function getFiles(folder)
{
 d.setAlert(false);
 camera.getFiles(folder);
}
 
function openFile(file)
{
 camera.openFile(file);
}

In getFiles(); as well as openFile();, notice we are calling the setAlert(); method of the UcompOSDockProxy and passing it a value of false.  This is to cancel the Dock alert we set on the UcompOS Portal’s Application Dock that we set in the AIR application the first time the user clicks on a resource.

That’s all there is to our HTML sub-application.

Configuring Everything as a UcompOS Application

Now we need to set up our application manifest for our simple Digital Camera browser application.

This should be very straightforward if you’ve reviewed some of my other UcompOS tutorials but for AIR applications, there are some special configurations you need to make:

<application>
  <source>
    <base>http://desktop.ucompass.com/Camera_Example/Camera_Example.air</base>
    <params>
      <param>
        <name>appId</name>
        <value>Camera-Example</value>
      </param>
      <param>
        <name>publisherId</name>
        <value>0E5CA255707A7E3F70F12D38B16B8D2A4C17413C.1</value>
      </param>
    </params>
  </source>
  <titles>
    <title locale="en_US" default="true">My Camera</title>
  </titles>
  <icons>
    <icon locale="en_US" default="true">http://desktop.ucompass.com/Camera_Example/icons/camera.png</icon>
  </icons>
</application>

Notice the appId and publisherId parameters you must include in the <params/> element of the manifest.

IMPORTANT: At the time I am authoring this tutorial, the evening of December 27, 2009, the publisherId field faces an uncertain future in AIR 2.0 and may be deprecated.  At present, you can find your publisherId by looking in the $APP/Contents/Resources/META-INF/AIR/publisherid file in the application installation directory for your installed application.  The appId and publisherId parameters must be included otherwise, the UcompOS Portal will not be able to successfully launch your UcompOS AIR application.  Any changes to the AIR 2.0 implementation specifics for publisherId will be blogged about here and updates will immediately be made to the UcompOS RPF accordingly.

Next we’ll take a very quick peak at my Dock Manifest:

<applications>
  <application>
    http://desktop.ucompass.com/Camera_Example/manifest.xml
  </application>
</applications>

In this case, I obviously just have a single application I am loading into my UcompOS Portal implementation that is our simple Digital Camera browser example.

Screenshot of the Application

demo

Conclusion

In this tutorial, we created a deliberately simple application to demonstrate a number of core UcompOS RPF concepts and principles – particularly integrating the desktop into a UcompOS Rich Portal Application implementation.

Proxy Components are Client Interfaces to Public API Methods

In my blog posting yesterday entitled A Services Dictionary Publishes a UcompOS Entity’s Public API Methods we learned that a UcompOS entity exposes functionality to other entities by publishing a Services Dictionary at the time the UcompOS SDK is instantiated.

The Services Dictionary can be thought of as a map that maps the name of a public API method to its internal implementation within that entity so as to not have to divulge the internal implementation details of the entity and its class structure.

This is the same concept as in a webserver configuration file.  You generally do not expose the internal absolute path of a virtual host, rather translate a domain or subdomain to resolve to an internal path on the local file system.

In the entity that originates a call to the public API method of another entity, the UcompOS SDK’s client infrastructure is leveraged.

Any data that is to be sent is packaged in an instance of an SDK class called a CommandObject which is then packaged into an instance of an SDK class called DataPackage which is the exclusive format of data that travels between entities in the UcompOS Continuum.

While it is certainly permissible to manually construct CommandObjects and DataPackages and then send them to the send(); method of the SDKClient Singleton (AS3 SDK documentation is available to help with this), it is far more convenient to set up a Proxy Component to handle this.

In advanced cases, you may find the need to call up functionality in a remote entity that is NOT exposed in the ServicesDictionary.  You can still do this but of course it requires knowledge of the remote entity’s internal implementation details and you have to specify the class path and associated method in the target entity.  This scenario does require the manual construction of a CommandObject and DataPackage and then a call to the SDKClient Singleton send(); method.

Proxy Components allow you to add more practical interfaces to the functionality exposed by a remote entity.

For instance, by strict convention, all methods that participate in UcompOS Continuum activity must receive one parameter of type Object.

You could create a Proxy Component however that masks this implementation requirement.

As I explained in my posting yesterday, the UcompOS SDK is packaged with a number of Proxy Components that represent the client interfaces to the public API methods exposed by the UcompOS Portal.

The UcompOS Portal is just another entity with the SDK installed in the context of the UcompOS Continuum.

As an example, we looked at the UcompOSWindowProxy class and specifically, its add(); method.

Let’s look at a simple example here to help explain this.

Suppose we have two UcompOS entities loaded into the UcompOS Portal.  One will expose a public API method, the other will call that public API method.

In the Services Dictionary of the entity being contacted, we may see a property that looks something like this:

'API.someMethod':{ static:true, classRef:APIClass,method:'testMethod',description:'A test API method'}

The classRef is the internal class path that houses the target implementation method, testMethod.  Notice there is also a requirement to articulate whether the method is static or not.

Let’s suppose our internal testMethod(); implementation looks like this:

public static function testMethod(data:Object):Object
{
 return {value:data.value*data.value};
}

Again, by strict convention, any public API method must receive exactly one parameter of type Object as input and return a value of type Object.  In this extremely simple method, we return the square of the value property of the Object passed to the API method.

In the entity that will call this public API method, we could create a Proxy Component.

All Proxy Components by strict convention MUST extend the SDK class AbstractProxyComponent.

Our Proxy Component class may look something like this:

package
{
 
 import com.ucompass.ucompos.sdk.client.AbstractProxyComponent;
 
 public class TestProxyComponent extends AbstractProxyComponent
 {
 
   public function TextProxyComponent()
   {
     super();
     super._destination = _sdkModel.parent;
   }
 
   public function squareNumber(value:Number):void
   {
     call("API.someMethod",{value:value});
   }
 
 }
 
}

Some things to point out:

  • The call method in our Proxy Component requires exactly two parameters – the public API method name in the remote entity and the Object instance to be passed to the method – this is the strict convention to be employed in Proxy Components
  • In the constructor of our Proxy Component, we are setting the value of the protected property _destination – this concept will be covered in a follow-up posting in the near future but for now I’ll point out that all entities have a universally unique identifier associated with them (UUID) that can easily be determined dynamically
  • In this case, since the _destination property is being sent to _sdkModel.parent, the implementation scenario would involve the entity that is publishing the public API method ‘API.testMethod‘ has launched the sub-application that will call the public API method – thus the target entity is the parent in this context and its UUID is accessible on the public property parent on the _sdkModel instance that is inherited from AbstractProxyComponent

And then to invoke the squareNumber(); method, you’d see something like this:

var p:TextProxyComponent = new TestProxyComponent();
p.squareNumber(5);

The call(); method of the AbstractProxyComponent class that all Proxy Components extend masks the implementation details of CommandObjects and DataPackages from the developer.  call(); provides a direct interface to the SDKClient Singleton send(); method that sends a DataPackage instance into the UcompOS Continuum bound for the target entity.

In tomorrow’s posting, I’ll talk about how you actually get data back from the public API method.  In other words, how we actually get the result from the squareNumber(); method in our Proxy Component.

This has to do with the asynchronous event handling implementation model in the UcompOS RPF that is modeled after the MVC (Model-View-Controller) design pattern.  (Is MVC really a Design Pattern?  Lott and Patterson seem to think so in their book Advanced ActionScript 3 with Design Patterns).

A Services Dictionary Publishes a UcompOS Entity’s Public API Methods

As I discussed in my posting yesterday, each application, sub-application, and the UcompOS Portal itself is considered an entity in the context of the UcompOS Continuum.

For an entity to play a meaningful role in the Continuum, it must have the UcompOS SDK installed and there is an SDK for Flash/Flex, AIR, and JavaScript UcompOS applications.

The SDK enables each entity to serve as both a client as well as a server as far as its ability to send requests to and receive requests from other entities.

The implementation details of the UcompOS SDK are well hidden from the developer, however, to build the most engaging and interactive experiences with the UcompOS RPF, a command of the core mechanics of the UcompOS SDK will serve you very well.

Before I continue, I recommend you take a look at the Video Tutorials entitled Services Dictionaries and Proxy Components that will provide a foundation for the client-server paradigm of a UcompOS entity.

Messages are sent back and forth between entities in the UcompOS Continuum in a format called a DataPackageDataPackage is a class in the UcompOS SDK.  Full SDK documentation is online for ActionScript and JavaScript developers.

The SDK class SDKClient is the interface to the UcompOS Continuum for outbound DataPackage instances and the class SDKServer is the interface to the UcompOS Continuum for inbound DataPackage instances.

The functionality an entity makes publicly available to other entities are considered that entities Public API Methods.  The list of Public API Methods that an entity sponsors are published in an instance of a class known as a Services Dictonary.

A Services Dictionary by strict convention will extend the abstract class AbstractServicesDictionary which is built into the SDK.

AbstractServicesDictionary furnishes a protected variable _map, which will be overridden in the extending Services Dictionary class instance.

_map is a simple Object where each property is an Object whose key is the name of a public API method and whose value is an Object that points to the internal implementation location of the functionality.

For instance, in the UcompOS Portal Services Dictionary, you’ll see the following property in the _map Object:

'MDI.addWindow':{
  static:false,
  classRef:com.ucompass.ucompos.controller.api.commands.MDI,
  method:'add',
  description:'Forms a new MDI window on the UcompOS Main Container'
}

MDI.addWindow is then considered a Public API Method sponsored by the UcompOS Portal.

You can sort of think of a Services Dictionary as being analogous to a web server configuration file where virtual hosts are analogous to public API method names and the local directory they resolve to are analogous to the mapping to the internal functionality that is leveraged when the public API method is contacted.

When the UcompOS SDK is instantiated, the static getInstance() method of the SDKClient class is passed a reference to the main application class (an extension of MovieClip or Sprite in a Flash application or an implementation of Application or WindowedApplication in a Flex application).

The syntax to instantiate the UcompOS SDK client is as follows:

SDKClient.getInstance(this);

and this command is generally going to be in the application’s main class either in the constructor of the main Document class in a Flash application, or in a private event handler in the main MXML document of a Flex application being called AFTER the applicationComplete event is fired.

The instantiation of the UcompOS SDK Client can accept a second parameter as well which would be a new instance of a Services Dictionary.  So suppose in my entity my Services Dictionary was a class named ServicesDictionary.  I would instantiate the UcompOS SDK as follows:

SDKClient.getInstance(this,new ServicesDictionary());

Once I do this, any other entity can easily target my entity’s public API methods.

I will add at this point that by strict convention, any public API method must be configured to accept exactly one parameter of type Object and return a value of type Object.  Any data that needs to be sent to a particular public API method must be encapsulated within the single Object parameter passed to it.

Also, the UcompOS SDK has been kept deliberately as simple as possible.  There are no Flex dependencies in it which is why you can use the SDK interchangeably in Flash as well as Flex applications so keep this in mind when packaging data for transmission across the UcompOS Continuum.  For instance, sending an ArrayCollection from a Flex application to the public API method of a Flash application will obviously not work.

An entity can target functionality in another entity even if that functionality is not exposed in the target entity’s Services Dictionary.  However in this case, obviously, the calling entity requires intimate knowledge of the internal implementation details of the target entity.

In my blog posting tomorrow, I’ll focus on the other side of a UcompOS transaction between two entities and I’ll introduce Proxy Components.  A Proxy Component is a client to the public API method in another entity.  As a brief foreshadowing, the UcompOSWindowProxy’s add(); method in the UcompOS SDK can be considered a client to the example UcompOS Portal public API method above, MDI.addWindow.

Further, packaged into the UcompOS SDK are a host of Proxy Components that represent the client interface to all the public API methods that are exposed by the UcompOS Portal.

More on this crucial topic tomorrow.