Parsley Model-View-Mediator Architecture

For those who have used Parsley as their application framework knows just how powerful it can be. However, there is something that has annoyed me slightly over time.

When I’m designing a system, I always try to use proper Flex practices. Practices like using MVC to separate components and business logic, making components truly encapsulated and reusable, etc. The problem that I find with Parsley is that it only allows you to use Injection based views for its MVC architecture; the View knows something, either a Presenter or a Model, and it’s always injected in by the Context.  The problem is, if you have several projects that need the same components but different frameworks, you can’t freely interchange those components between projects since the view is tightly intertwined with the Parsley injection.

A way to solve this by using the Mediator pattern (The View knows nothing, but the Mediator knows about the View) because it makes your view extremely portable between projects and forces the developers to use better practices since the only way to communicate with the Mediator is through events.

Luckily, Parsley has several extension points which you can insert custom classes to change or add functionality.  This gave me an opportunity to create my own parsley tag aptly named ‘Mediator’.  What this allowed me to do is to create a Mediator class that is controlled by Parsley and when the view is created; an event would get dispatched from the View and Parsley would then create a Mediator class and inject the view into it.  This way, the view never knows anything about the framework which leaves the components to be freely interchangeable between projects.

WARNING: The following code only works with Parsley 2.3 and higher.  I made it this way because some major changes have been made to the extension points in 2.3.

You can download the sample application I made and look at the files. All you really need is the Mediator library swc and put it in your project.  Then you need to specify that you Parsley context will use this Mediator extension by doing the following.

<!-- Initialize Parsley like you would normally -->
<spicefactory:ContextBuilder config="{Config}">
	<!-- Except add the mediator configuration within it -->
	<!-- Alternatively, you can use Mediator.initialize(); instead of the mxml tag -->
	<mediator:Mediator />
</spicefactory:ContextBuilder>

And that’s it. By including the Mediator class within your Context, Parsley knows how to change the extension point for it to work.

UPDATE: Instead of giving you the raw files, I’ve packaged them in an easy to use library.  You can now find the source for the library here.

UPDATE 2: I’ve updated the files for the latest 2.3M3 changes in Parsley.

UPDATE 3: Parsley 2.3 came out recently and I’m happy to say that my Mediator still works.