Flex best practices

Question

Im new to Flex but I have plenty of experience using traditional webdev technologies (HTML, CSS, JS/AJAX, PHP).  I know that when you build a web app using these technologies, it's considered best practice to use event listeners rather than event handlers in JS, and to place all your JS in an external file and reference it in your HTML page. I've been watching several videos on Lynda.com on Flash Builder 4 and Flex, and in all the videos, the author places most of the Actionscript in the MXML file while referencing a few custom Actionscript classes. With that said, what do Flex developers typically do?

Answer 1

In Flex 3, it is considered best practice to use the Presentation Model pattern (as advocated by Martin Fowler), where you extract the view states and view logic.
A PM is a simple ActionScript class that extends EventDispatcher (for Data Binding purposes).
[Bindable]
public class SalesProjectionPM extends EventDispatcher {
     // Collection of QuarterlySales objects
     public class quarterlySales:ArrayCollection;
     // Event handler
     public function viewSwitchHandler(event:MouseEvent):void {}
You can then inject this PM into an MXML view using an IoC container framework and bind your view to the corresponding PM for both your components dataProviders and events. If you have a central data model, you can inject it into your PM and bind to it.
In Flex 4, you already have the separation of view and logic that comes with the new Spark Architecture. You have an ActionScript component that contains the view states and view logic (including event handlers) on the one side. And you have a MXML skin that materializes the UI on the other.
You add/remove event handlers in the partAdded(), partRemoved() overriden methods. If you have a central data model, you can inject it into your ActionScript components.