Cairngorm Modularity…

Using modules in Flex isn’t all that difficult to understand. But as I have read on many a blog, using Cairngorm with modules is giving people fits. Well, not me…

You use modules so that you can load a portion of your application (functional or visual) and unload it independent of the main application. You do this (using Flex Builder) by extending mx.modules.Module either in a different project or the same, making sure your component is registered as an application in the properties. This Module Component then can be loaded into your main application (shell app) by use of the ModuleLoader class. Simply set the attribute ‘url’ on the ModuleLoader (which is a DisplayObject) and YourModuleLoaderID.loadModule() and YourModuleLoaderID.unloadModule(). If the module is a visual component it will be loaded wherever you place it. Likewise you can place a non visual module anywhere and reference it by id. This is where the difficulty starts.

Now that you have a loaded module, unless it’s a trivial thing, you are going to want to interact with it. With Cairngorm this is very interesting. All sorts of things can happen when you get an application running with the FrontController and ServiceLocator patterns then you just up and load an entirely autonomous Cairngorm implementation in the same player. So don’t. The interaction between module and shell application is communicated by implementing interfaces. If you are going to be using Cairngorm in the base or shell app, then you need to use IoC (inversion of control) to plug a Cairngorm based module into the shell. Specifically, your module will more then likely be using the FrontController to register events/command pairs and it will need to use the shell app’s ServiceLocator to access services. You can easily create an interface that allows you to pass these two items to the module being loaded and if your like me, you can even extend the Module component to make a lot of things happen in the background.