These apply to Flex 2.0.1 with any version of Cairngorm. Since people’s programming background varies in Flex, these are not facts, just my opinions based on my experiences using ARP & Cairngorm for over 2 years. Furthermore, there are alternatives to Cairngorm, I just cannot try them as much as I like. Now that I’m doing product work, I can’t just “try this framework on this new project”. I live in the same code base longer supporting existing clients, and can’t do dramatic re-factoring without getting fired.
1. If Cairngorm looks complicated, don’t worry, it is, and you’re not alone
“Bunch of code on _root vs. all of these classes and conventions? This’ll take forever!”. It takes getting used to. I felt “comfortable with Cairngorm” on my 4th project with it. To this day, I still mod it though, and try different things. As more people come into Flex, there are more cool ideas and techniques floating around.
2. If it feels like it’s taking a long time just to do something in Cairngorm, it does.
“OMFG… 3 classes just to execute what would take me 1 line in Flash? Lamesauce!”. Code gen can help here, at least at the beginning of the project.
3. Only Commands set data on the Model; you can break this, just don’t if you can help it.
In Model View Controller, only the Controller sets data on the Model. In this case, the Commands are the Controller (usually), and as such, setting ModelLocator data is their job, and their job alone. If data is getting f’d up, you immediately know it’s in the Command. You never have to question “who’s setting my data, where, and when?”.
4. Delegates make the server call and parse the data (sometimes in a Factory)
This has only happened once in my career: I was hitting PHP for the back-end, parsing XML, and in the middle of the project, we switched to OpenAMF and Java where I had to parse objects. Using Delegates means you only have to re-code your Delegates, not the rest of your app. The Commands still get the same data.
The only reason I use Factories is because A) parsing can be a lot of code and you don’t want to make your Delegates look more complicated than they are and B) you can share parsing routines easily in the same Factory class.
5. If you see a Command parsing data, it’s coded wrong.
Parsing is differently from filtering, modifying, and assembling. IE, making Value Objects from XML should be done in the Delegate, not the Command. Making associations between ArrayCollections, injecting default values are both ok. Remember, the key here is if the Command is touching raw server data, you’re either not using Delegates correctly, or have AMFPHP/FDS/WebOrb working correctly, hehe.
6. There are 3 ways to use Commands & Delegates. I prefer A because it’s consistent, leads to short class files, and is very explicit.
A) For every use case, you make 1 Command and 1 Event. This can sometimes also mean 1 Delegate. (ie, LoginEvent, LoginCommand, LoginDelegate)
B) For every use case that’s related, you can consolidate them into a package path. So, Login, ChangePassword, and ForgotPassword would all be in the same class. You’d then use constants to determine which one to run. (ie, LoginEvent has LOGIN, CHANGE_PASSWORD, and FORGOT_PASSWORD as String constants. Your LoginCommand has a switch statement which determines which one to run. Your LoginDelegate has 3 methods; login, changePassword, and forgotPassword that your Command can use.
C) Variances on B. Maybe 1 Event and 1 Command, but multiple Delegates. This is not a cop-out bullet item, rather, I’ve seem many derivatives that can all be traced back to “B with mods”.
7. ViewLocators are considered bad practice.
That said, there are developers who still love and use them. The use case, however, is valid: Having a View “know” when something in a Command has occurred. I use callbacks, some set data on the Model to trigger callbacks on the Views (maybe via a setter function), and some use addEventListener in tandem with CairngormEventDispatcher.
8. ViewHelpers are considered bad practice.
That said, there are developers who love the idea of “code behind”. I’ve yet to see a consistent theme on the blogs and mailing lists. There are 2 reasons that are common:
A) They don’t like mixing ActionScript & MXML.
B) They want to separate their View’s from their “View controller code”
Some use the script tag to point to an external file (lame in my opinion; you have to define your controls as member variables and you end up with twice as many View classes). Some use inheritance where you extend your GUI MXML. Others take the reverse, and have the GUI MXML extend the ActionScript ViewHelper. Some will even take the Composition over extending MovieClip approach I’ve seen a lot of coders do in Flash. Instead of their ViewHelper extending a view class, it’ll instead take a UIComponent as a parameter, say in an init method, and use that UIComponent via composition.
To me, you’ll get over it as you get more comfortable with Flex. Code your components in MXML with code up top in a script tag. If you really need efficiency, or start doing some really low-level, abstract type classes, then you can start coding your components in ActionScript. If you want to get stuff done today, use MXML.
9. Don’t use flash.net.Responder, use mx.rpc.Responder instead.
Yes, it’s frustrating because Flex 2.0.1 doesn’t give you the source, but in my opinion, Flex Builder doesn’t handle same-named classes very well. Just go with what Flex uses, and call it a day. If someone requires flash.net.Responder, code a wrapper to bring him into Flex land. “Sir… you need a tie to get into this restaurant. We have one in the back, one moment.”
10.Try not to have View’s use CairngormEventDispatcher (or Events that extend CairngormEvent use event.disaptch()).
Instead, have those deeply nested views dispatch events. Either bubble them up so a master controller View can then fire off Cairngorm events, or bucket-brigade them up. The most common scenario is itemRenderers that are a custom class in DataGrids.
- make the itemRenderer class. If you have something in it that is clickable, dispatch a custom click event. Make it bubble.
- extend the DataGrid that uses your custom itemRenderer, and put the custom event in the metadata up top. Otherwise, the class that houses the DataGrid will only be allowed to subscribe to the event via MXML, only ActionScript. If you use MXML, it’ll fail to compile because the DataGrid doesn’t have that event in it’s source code.
It may feel cool at first to have a LoginForm for example dispatch the LoginEvent, but if you need to use it for a different purpose elsewhere, you’re screwed; it’s hard-coded to use a specific CairngormEvent. This applies to all components. Encapsulate your components and do your best to do what BT does: “bubble it up”.