Tcoz Tech Wire

Discoursing on trends and technologies interesting to Tim Consolazio, sole proprietor of Tcoz Tech Services, specializing in Flash/Flex/Air, iPhone, Facebook, Twitter, and related technologies.

"Technology from an indie software developer's perspective".

Monday, May 25, 2009

TcozTwitter: A Twitter Client using Adobe Air and the Flex Mate Framework - Day 1

QuickStart: This subject of this article is a project that satisfies three goals:

- To complete a practical exercise of using the Twitter API.
- To create complete a practical exercise of using the Flex Mate framework.
- To have a Twitter desktop client that works *exactly* the way I want it to.

To that end, I decided to build a Twitter client, using Adobe Air and the Mate Framework.

Onto the discourse...

Why this group of technologies?

Twitter: If you're reading this article, I don't have to tell you why it's important, as a developer, to do more than dabble with it.

Air: I really like building Air apps. At it's most basic level, you could say that Air is Flash running on your desktop in a native dedicated runtime manager (called "Air"). Freed of the browser sandbox, Air has a lot of capability Flash doesn't, like real local file access and data storage, and doesn't suffer from some of the general performance issues of the browser-based Flash player. The NY Times has dumped Microsoft Silverlight in favor of Air, as has the Major League Baseball tech organization. It's a pretty exciting technology, and if you're already good with AS3/Flex, the learning curve is more a speed bump than a hill; write one Air app, run it on any machine with it's OS-specific runtime installed.

Mate: I'm predisposed to being dubious of Mate, because I prefer frameworks and patterns that translate to as many technologies as possible, and I prefer to avoid markup for UI layers whenever possible, because it tends to create scripted spaghetti. PureMVC, for example, is easy to implement in just about anything, and inclines the developer to some level of genuine C-style OOP. Mate, on the other hand, is inherently Flex targeted; it makes heavy use of Flex MXML and databinding. But, love it or hate it, I realized a while back that avoiding MXML isn't good for my business, so I skilled up, and these days a lot of people are loving Mate, so I should get a working knowledge--though I will say, this is often the case of things that make a complex technology seem easy, and it all collapses once you hit big apps.

If you want to know more about the Mate Framework, go to the Mate Flex Framework Home Page. There you can find the SVN and/or SWC downloads, tutorials, etc. etc.

Add these three things up, and it'd seem that, if I put in the time, I'll have a pretty cutting edge Twitter desktop client, insofar as the technologies involved to make it work are concerned.

Anyway, down to the bits 'n bytes of Day 1, TcozTwitter. I'll assume you know about things like Flex, working with APIs, and so on.

As I said, I have mixed feelings about Mate; it's true that it's pretty easy to learn and get working, which no doubt contributes to it's popularity. People talk about it like the second coming, and say that it doesn't prescribe a particular kind of development, your app isn't tied to it, etc. But from what I can see initially--granted I'm no Mate expert, but I've worked with other frameworks pretty deeply--this isn't true. Your app is VERY tied to it.

For example, Mate prescribes how you use events in a VERY particular way. Events dispatched directly from non-views (typically "managers" in Mate parlance) don't hit the all-important EventMap (essentially a clearing house for event handling), because in Mate, you bubble all your events up to the top-level application for handling, and bubbling is a function of the DisplayList; non-views need not apply.

There is a workaround; in the non-view, create an instance of a GlobalEventDispatcher and use that to dispatch the event so that it immediately hits the top level app, which contains the main EventMap, but that's not at all what I'd typically do; usually I'd just have the non-view extend EventDispatcher, either directly or in a base class, and dispatch away. I was surprised by this; in Cairngorm or PureMVC, the basis of how you dispatch an event isn't prescribed by the framework; what you do with that event once you catch it is. I guess this is a matter of perspective, and no doubt this statement will annoy the Mate advocate, but there it is.

Note: I don't dislike Mate. It's growing on me. But at this point I still prefer PureMVC. This may change over time, we'll see.

If you'd like to try some Mate twittering yourself, for your first Twitter call, here's a simple MXML fragment showing what to put in your MainEventMap (which is essentially a manager for handling bubbled-up events in the Mate framework):


<mate:EventHandlers type="{Event_GetLatest20Public.GET}" debug="true">
<mate:HTTPServiceInvoker url="http://twitter.com/statuses/public_timeline.xml" resultFormat="xml">
<mate:resultHandlers>
<mate:MethodInvoker generator="{Manager_Tweets}" method="storePublicTweets" arguments="{resultObject}" />
</mate:resultHandlers>
</mate:HTTPServiceInvoker>
</mate:EventHandlers>


Notice in there we have an HTTPServiceInvoker pointing to the twitter endpoint that dumps out the latest 20 public timeline tweets. You can grab them in a variety of formats just by changing the extension of the public_timeline call (instead of .xml, use .json for example). This is strictly preference; I like XML, so that's what I'm using. In addition to this, you'd have to write your Manager_Tweets class, with the "storePublicTweets" method, and dump it onto a model for binding and so on. If you need a primer that shows you how to set this all up (it's very easy), go through this tutorial. I used this as as starting point for my Mate explorations a while back and it was very helpful. While there's certainly a lot more to learn about Mate, understanding how the EventMap works in conjunction with Managers is the most important part, and this tutorial makes it very clear.

With all that understood, my first effort was to take that XML and bind it into a TileList, which has an itemRenderer that receives the individual data objects, which have properties that map to the original XML elements. So, in the itemRenderer, just by setting the image component's source to "data.profile_image_url", and the top text components text property to "data.name", I get the expected result; a scrolling TileList of the latest 20 public posts, with profile images and names.

It's not pretty; I didn't work out the sizing or layout, or scrolling, etc. This is entirely the first step. But hey...I've got an Air client, using the Mate framework, hitting the Twitter API and displaying user data. I'm on the way to achieving the three goals I mentioned at the top of this article.

So far so good. Next step; clean up that UI to display the scrolling list more neatly, and add in the message and metadata to that display of public posts.

As usual, thanks for stopping by. Pic of in-progress client below:




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