Now let’s look at the Flex service layer, which comprises the classes where we define the data services we’ll access, the definition of the service methods we’ll access, and the logic for calling those services and what to do when the services return.

Getting Organized with Cairngorm

The first, and certainly the most popular, framework for Flex applications is called Cairngorm. Cairngorm was created by Steven Webster and Alistair McLeod, who ran iteration::two, a consulting company which later became the EMIA RIA practice of Adobe Consulting. Cairngorm is now an open source product distributed by Adobe Labs (http://labs.adobe.com).

Let’s get this bit out of the way too, because a lot of people hear the name and reply with a quizzical look: Cairngorm is a funny name, yes. It’s named after a mountain in the Nevis mountain range in Scotland. iteration::two was using Scotland mountain ranges as code names for internal libraries, and Cairngorm stuck after it went public.

Cairngorm is a micro-architecture, which means that it’s more like a set of patterns to aid in architecting an application.

It also has nothing much to say about how you architect the view of your application either; it’s mostly about how you glue the interactions between the different pieces of your application with each other and with the services that support the application.

Cairngorm helps developers architect the application according to the Model-View-Controller (MVC) principle, which is common to many visual applications. MVC distributes responsibility of components over three types of classes: the model, which holds the data; the view, which displays that data; and the controller, which brokers the interactions on the view with the data in the model, keeping the view and model uncoupled.

Cairngorm gives developers a model in the Model Locator, and a controller, which is a collection of commands (we’ll discuss these shortly). The view is pure Flex and makes good use of Flex’s powerful binding framework.

Cairngorm employs a set of best-practice design patterns to help you architect your Flex application in the most flexible (no pun intended) way possible. Table 10 lists some of these patterns.

The best place to learn more about the interactions within Cairngorm is at http://www.cairngormdocs.org.

A typical interaction with Cairngorm goes as follows:

• User gesture
• CairngormEventDispatcher
• Command
• Delegate
• Service
• Command (as Responder)
• Model
• View changes (through binding)

Generating Cairngorm Classes

As I mentioned in the discussion about tools, Cairngorm projects go a lot smoother with some code generation. Cairngen helps out by providing utility Ant tasks and template files to fit your project’s needs. Some of the tasks include those for generating the common Cairngorm directories in your Flex package structure, and those for generating a ModelLocator, ServiceLocator, and FrontController. These tasks are especially helpful at the beginning of a project, but not much after that. I find Cairngen most useful in generating what it terms a “sequence”: a CairngormEvent, a command, and possibly a delegate with similar names and a string constant on the event as a unique identifier to put into the FrontController to register the event to the command.

If you download Cairngen yourself, you’ll get a build.xml and project.properties file, and a config and template directory. I’ve moved the contents of that build.xml to our ui project build.xml: feel free to look that over, but we won’t need to change anything there.

I also renamed the project.properties file to cairngen.properties, but left the config and template directories as is.

Notice in Figure 17 that the templates directory contains just the templates for the different types of generation of Cairngorm 2.2 classes. You can modify those templates to fit the needs of your project (e.g., match the brace style your team uses, add comments, etc.).

Figure 17. Cairngen Files

The only configuration you need to do is inside the cairngen.properties (formerly project.properties) configuration file:

############################### FLEX BUILDER PROPERTIES 
root.dir       =./src/main/flex

################################# PROJECT PROPERTIES 
project.name   =Bookie
com.dir        =lcds
domain.dir     =examples
project.dir    =bookie
namespace      =${com.dir}.${domain.dir}.${project.dir}
project-uri    =${root.dir}/${com.dir}/${domain.dir}/${project.dir}

################################## SOURCE MANAGEMENT 
overwrite.existing.files =false

################################ CAIRNGORM PROPERTIES 
cairngorm.version  =2.2

################################# CREATING SEQUENCES 
sequence.name      =BooksChosen

################################### CREATING VOs 
vo.name            =HelloWorld

Here we tell Cairngen where the source goes, the name of the project, and information about the package structure. Here’s a list of the Cairngen tasks:

Get your copy of Tony Hillerson's Enterprise Application Development with Flex.

• clean (remove all Cairngorm-standard directories and as well as the model, service locator, controller, sequence, and VO)


• create (create Cairngorm-standard directories; generate the model, controller, service locator, sequence, and VO)


• create-cairngorm-directories (Cairngorm-standard directories)


• create-front-controller


• create-model-locator


• create-sequence-exclude-delegate


• create-sequence-include-delegate


• create-service-locator


• create-value-object


• delete-cairngorm-directories

The tasks I end up using most are create-sequence-exclude-delegate and create-sequence-include-delegate. These tasks take the property called sequence.name from the properties file and generate an event called Event and a command called Command. The include-delegate version makes the command an IResponder (with a result and a fault method) and creates a Delegate class. This is for use with commands that are meant to call a service method. I usually move the generated delegate’s methods to a single consolidated delegate class.

Each time you want to generate a new sequence, you edit the properties file to add the name of the sequence you need, and then run the applicable Ant task.

Next time we'll continue looking at the components of Cairngorm as we finish looking at the Flex service layer. You can always find the entire series here.