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December 17, 2007

Can Cairngorm and Modules play nice?

Let me say, first off, that my wife gave birth to a beautiful baby girl on Wednesday morning, and they are doing just fine. I've been relocated to the spare bedroom so that I can actually function during the day, however I'm missing about 30 hours of sleep this week that I'll never get back. Having said that, I am blogging today because even though I've sort of fixed my latest issues, I'm not entirely sure I've used the best approach.

This is really a sequel to my previous blog... I am still fighting with getting modules to load properly and independently of each other and the shell flex application. Here's the deal...

I have one complex flex module that is built on the Cairngorm 2.2 framework. In itself, the module works fine, and after the progress from the other day, loading multiple instances of the module into a simple shell works fine too. However, when I tried loading multiple instances of the module into the actual application, things died. Why? Because the shell is built on the Cairngorm framework as well. The minute I add in the line to my shell app, subsequent instances of the module don't load properly. I determined that the shell needed to use a different controller than the module, but that wasn't enough (though still necessary). There were funky things happening again when events were triggered - weird casting errors, events firing across multiple module instances, shared models, etc.

A couple of observations:
CairngormEventDispatcher basically returns a singleton. If the shell app gets an instance of this class, then any Modules that load will use the same instance. So, adding the appcontroller to the application will in fact get an instance of the dispatcher. Running through the debugger, I noticed that as I loaded each new instance of the same module, event listeners were added to the singleton's eventDispatcher. So, say your module was listening for the ContactEvent.LOAD_CONTACT event. If you loaded 3 instances of that module, your controller would execute 3 commands, once for each module.

When an event is received by a command, and you try to cast that event back to its origin, i.e. ContactEvent(event), it will only work in the module that actually originated the event. The other modules will throw the following exception:
" cannot convert com.crazedCoders.moduleTest.event::ContactEvent@4b23281 to com.crazedCoders.moduleTest.event.ContactEvent." Trying to test for it, i.e. if(event is ContactEvent) doesn't work since the event is in fact a ContactEvent. Very frustrating.

If you do not use any Caingorm in your shell application, you will not run into these issues, so for some that might be the quick solution. Sadly I was not afforded that luxury, so I had to find another way.

Since I was trying to treat each Module as an autonomous mini-application, I decided that I needed a CairngormEventDispatcher specifically for each Module and the Application. I created a Factory Class that would do just that. Here's the code:

package com.adobe.cairngorm.control{ import mx.modules.ModuleManager; public class CairngormEventDispatcherFactory { private static var instances : Array = new Array; public static function getDispatcher(obj:Object) : CairngormEventDispatcher { // in order for each module developed using cairngorm to be able // to work independently of the shell and other modules, // we need to create a hash map of cairngormeventdispatchers // that are keyed on module instance or application. // This prevents cross module listening for events, // which is beneficial especially when loading multiple instances // of the same module var ed:Object = ModuleManager.getAssociatedFactory(obj); var parent:String = "application"; if(ed != null){ trace(; parent =; } if(instances[parent] == null){ var cgDispatcher:CairngormEventDispatcher = new CairngormEventDispatcher(); instances[parent] = cgDispatcher; return cgDispatcher; } else{ return instances[parent]; } }}}It took me a while, but eventually I stumbled upon ModuleManager.getAssociatedFactory(object). This function *seems* to be able to figure out within the context of which Module (if any) the object was instantiated. If an object belongs to the shell, it returns null, if not, then it returns a ton of information, including a name property that contains a unique name i.e. instance77 for the loaded module. I create a new instance of the CairngormEventDispatcher for each instance and stuff it in the static associative array, then I replace the usual CairngormEventDispatcher.getInstance().dispatchEvent(...) with
Now the application shell and each module gets it's own singleton, and the overlap seems to be taken care of.

Again, I welcome any feedback. I'm not particularily fond of this solution, and I hope someone out there can offer a better one.

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