This is the second part in the introductory series covering Robotlegs AS3 here on InsideRIA. In the first part in the series we learned what Robotlegs AS3 is and had a brief 'HelloWorld' introduction to the Robotlegs Context and Mediator classes. This article is going to expand on those concepts and introduce Models.
If you missed it, here is Part One: Context and Mediators
What is a Model?
Model classes encapsulate your application's data and provide an API to access and manipulate that data. The other classes in your application will make requests of models via this API. When data on the model is updated, the model dispatches events that the other classes within your application can react to. Models are appropriate for capturing the domain logic, such as performing calculations or other manipulations. An example of this might be a shopping cart. When an item is added to the shopping cart model, the new total for all of the items in the cart will be calculated. The new total will then be stored on the model for access by other classes within the application. By placing this logic within your models, you ensure that it isn't scattered across the entire application and know exactly where to look to see how and when your data is being manipulated.
In addition to controlling access to data, models maintain the state of your application. State, in the sense of the data model, is not the same concept as a Flex State, which relates to controlling the appearance of your application. They are certainly related, but with a model, consider a list of objects. You want to keep track of which of these objects is selected, so the data model has a selected property which is updated with the currently selected item. Other areas of your application can now access this property to discover which item is selected and react accordingly.
Models can be written to be portable. Along with Services this is something to keep in mind when you develop your models. There are many common sets of data that can easily transport between one application and the next. Think of, as an example, a UserLoginModel or a ShoppingCartModel. Portability takes a bit more thought and energy, but no more than writing the same code over again for each project does.
The model deserves a lot of attention. It is the core of your application. The visual components get all the ooos and aaahs, but as a developer you know that data is the man behind the curtain. It is our jobs, as developers, to curate the data and deliver it to those beautiful interface items accurately. This is why isolating domain logic in the model is so important. By isolating it you have made it easier to locate, update, and maintain. With the basic definition of the model in hand, let's look at a small example application.
On to the code!
This pure AS3 application is making use of Keith Peters's awesome Minimal Comps library. Don't worry, if you love Flex (and how could you not?) the next example will be a Flex app, but Minimal Comps makes it so easy to make quick examples with AS3, and Robotlegs is just as easy to use with a straight Actionscript application as it is with Flex. So let's take a look at the application and take it apart to examine its pieces.
Above is the application we will be examining. It is a simple list of authors with a quote displayed for the author that is selected in the list. Here is the archived Flash Builder project (zip 168k), which includes the Robotlegs 1.1 and MinimalComps SWC files as well[...]
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