Delegate Factories with Prana

I've been having fun with Prana lately. Prana is an IoC container framework for Flex under development by Christophe Herreman. Prana is sort of built with Cairngorm in mind, but it could work for any configuration and injection you wanted to do at runtime.

One of the benefits I can see is for rapidly prototyping an application with little to no knowledge of the service you may need to connect to for your data needs. If you can define the data model well enough, you could build your application with Cairngorm in such a way that all you'd need to do is change one file (or type of file): the Delegate.

That's the reason for the business delegate: to keep the application isolated from the implementation of the service layer.

I've written up an example of how I'm currently using this on a project and posted it at http://labs.effectiveui.com/examples/prana/delegates/. It's a pretty lame sample, but if you right click and select "View Source", it shows how I have created a DelegateFactory that gives my commands a Delegate that conforms to a certain interface. Then, using Prana, I can configure the DelegateFactory to build whichever implementation of the Delegate I wanted, without recompiling the application.

The benefit is that I can drive the application's data from dummy xml data, but the application doesn't care where that data comes from. As long as I'm write about the way the data looks, my Commands don't need to change once I switch over to a production ready Delegate.

First, look at the DelegateFactory. Notice that it contains a string, _delegateClassName which will contain the qualified name of the class I want the DelegateFactory to make. There's some type-checking in there once that string is set to make sure that points to a class that conforms to the interface. One last thing to notice is that I need to have the class of the delegate referenced at least once in the code so that it's compiled in. That happens on the line that says

private static var compileTheseClasses:Array = [DevDelegate]


So DevDelegate is the delegate I want to use at development time. That Delegate acts like a regular delegate that calls an HTTPService to get some xml. Instead of doing that, though, it just loads xml local to the swf and sends a ResultEvent to the LoadPeopleCommand as if a result had just returned from the HTTPService.

Once last thing to notice is the applicationConfig.xml which drives Prana. It's loaded by the InitializeCommand. In that first block there:

<object id="delegateFactory" class="com.effectiveui.examples.business.DelegateFactory" factory-method="getInstance">
<property name="delegateClassName" value="com.effectiveui.examples.business.DevDelegate" />
</object>


I tell Prana to configure my DelegateFactory with the delegate class I want to use. I can change this xml file at runtime, so as long as I make sure the Delegate is compiled in, I can change delegates whenever I need.

Of course that's just one of the uses of Prana, but I really like the ability to get up and running easily by making a development time delegate.

Flex needs a Custom Metadata Class

At MAX, I was really surprised to find out a sekret Flex compiler feature: You can keep custom metadata around in your Flex app. There's a tutorial with a really sweet proposed application for that feature at Christophe Coenraets' Blog.

The only thing about that example is that the entityManager needs to know to read the objects passed into its save() method for metadata. That's not a problem for that use case. BTW, you can read metadata with describeType()

What if I wanted to copy more of the JPA with Flex? Then I'd need the FPA (a mythical Flex Persistence API) to manage the instantiation of the EntityManager and pass in a reference at runtime. I'd need to inject the right EntityManager into any code that wanted it. Right now to do something like that we'd need to read every class, or intelligently read certain classes, to figure out if there were annotations to deal with.

It'd be nicer if we had a first-class Metadata class that got instantiated by the framework at runtime and knew about the class it decorated. That way it could do things like negotiating with the "FPA" to get the right EntityManager at runtime based on configuration data. It could then modify the object that had the metadata with no developer intervention. It'd look something like this, following Christophe's example:


[PersistenceContext(id='applicationPersistenceContext')]
public var entityManager:EntityManager;


That would mean that at runtime, the 'applicationPersistenceContext' persistence context, which could contain data about which database in SQLLite to use, maybe usernames and passwords or something like that... in short: configuration you don't want compiled into your code. That PersistenceContext object would know to inject the correct EntityManager into the variable 'entityManager'.

I think it'd be a great addition to the framework which would allow a lot more use of the "Dependency Injection Pattern" to help make easy to use frameworks for specific needs on top of Flex.

I've created an enhancement issue here: https://bugs.adobe.com/jira/browse/SDK-13002 If you agree, make sure you vote on the issue.

A Haiku for Jaiku

So I don't know if Jaiku is pronounced hai-ku or yai-ku, but here's a haiku anyway:

Google bought Jaiku
I really envy those guys
With all that money

RubyAMF makes me happy

I've been excited about RubyAMF for a while, and I finally got a chance to try it out after I worked it into my MAX presentation last week.

Aaron Smith was there at MAX too, and once we met and talked I weaseled my way onto the project. Score!

Anyhow, I've got a lot to figure out about how things work, but I really love these two technologies, Flex/Actionscript and Rails, and I'm really excited about what Aaron has already accomplished getting a very easy integration path between the two.

So, hopefully I can contribute to the stability and longevity of RubyAMF, and people will love it and it will achieve world peace or something.

eBay Wins!!

eBay Desktop, created by EffectiveUI and product managed by Alan Lewis of eBay, has just won a MAX award! Nice work!

Wait... this just in.. we won a MAX People's Choice award too!

Awesome!

MAX Day Thermo

We've been hearing about Thermo for a while now, and yup, it's pretty sweet :)

Basically it's the best "design view" ever made, and it works for Flex. Designers can import Photoshop files (!!!!) and turn graphic assets into skinned Flex components using metaphors that they're used to, like layers and graphics tools.

Have a look at Aral's blog, where he's just uploaded 3 videos of the keynote today - it's a better explanation than I could give.

MAX Day One

Internet connection is a bit spotty, and I was running all over the place yesterday, so I'm a day off, sorry.

Best session yesterday was "Flash Internals" by some guys from the Flash Player team. Those guys were geek's geeks. Good information about the pieces of the player and how separate the renderer is from the part that runs the code.

My talk on Flex with Rails went fairly well except RIGHT as I was about to show the fruits of my labor during the code walkthrough, my COMPUTER... my fancy MAC BOOK PRO CRASHED. So that was pretty annoying, but I have another shot at it on Wednesday. Hopefully that one goes better, but still, I think I was able to spread some good word about Flex with Rails and why Rails has the best development experience of the available back end languages.

Got to meet Aaron Smith of RubyAMF fame, who graciously came to my talk. Got to introduce him to a appreciative crowd. We talked about a few things afterwards, a few ideas and Rails performance. Really great guy.

After that some of the EffectiveUI crew hit the streets with some of the Flex team till late. Made it hard to make the Keynote this morning. I'll have a post about Thermo soon :)

Flex and Rails resources

Thanks for coming to my talk at MAX on Flex with Rails. I really wish my computer wouldn't have crashed right before the last part of my presentation, so I'm glad you actually found this post since I never got to show it up on the big screen.

Here are some of the resources that can point you in the right place when you're starting on integrating Flex with Rails:

Books:
Pragmatic Programmers has the definitive word on Rails.
Flexible Rails was the first book to start talking about Flex with Rails and what a great match they make.

Interweb:
Peter Armstrong - author of Flexible Rails.
Aaron Smith - RubyAMF is an AMF implementation for Ruby
Derek Wischusen - flexonrails.net
Daniel Wanja - onrails.org
The Midnight Coders - Creators of WebOrb for Rails.

Let the MAX announcements begin...

Adobe acquired Virtual Ubiquity! Grats to the Buzzword Peeps, grats to Adobe...

Now, what other big office suite names are out there? Hm.....