My initial impression of Adobe AIR was that it was some sort of “Flash for the desktop” deal. Developing apps in Flash didn’t really appeal to me so I dismissed it (bad memories Flash development using early versions of Macromedia’s tools).
Fast forward to a few weeks ago, I started experimenting with Twitter (basically publicly broadcasted instant messages). In so doing I looked at a number of desktop clients, of which it turns out there are a several that run on the Adobe AIR runtime. One of the first AIR twitter clients I tried was Jonathan Snook’s Snitter. Being a Snook creation it looks great (and of course, lime green by default). It’s even got a little notification area (née systray) icon for when it’s sitting in the background minimised.
There’s nothing that belies the fact that this is really just an AJAX-y web application without the browser. It consists of just a bunch of HTML, CSS and JS files sitting in my Program Files directory (C:Program FilesSnitter to be exact). I had a bit of fun opening them up in a text editor and hack around with them and was pleased to see that Mr Snook is a also a jQuery fan.
So an AIR app is just a client-side web app: HTML and CSS for layout (oh and Flash if you want as well), JavaScript for your logic plus some platform interop library-type stuff provided by the AIR runtime all hosted in an implementation of WebKit, the standards-compliant rendering engine also used by Apple’s Safari. Oh and it’s cross-platform: running on Windows, Mac and Linux (eventually).
None of this is new though: Microsoft had the same idea about 10 years ago that you could develop desktop applications in DHTML, CSS and JavaScript/VBScript by hosting the Internet Explorer rendering engine in a bare window and allowing the script access to the host operating system. This technology was called HTML Applications, or HTAs. Many of the Control Panel applets in Windows XP (e.g. User Accounts, Help and Support Center) are HTAs and I think at some point even some versions of Microsoft Money were too. Interestingly, with HTAs, you can if you choose, package all the HTML, CSS, JS, images etc inside an EXE or DLL as resources (served up using the “res://” protocol) rather than having them lying around loose on the file system. To create an HTA: create a web page, rename it to have an *.hta file extension then double click it. It will be opened up by MSHTA.exe – essentially Internet Explorer without any menus or buttons and with a more relaxed security policy (insert cheap IE security jibe here). HTAs have been standard equipment on all versions of Windows since at least Windows 2000, so are a good choice for creating things like custom setup programs when you can’t be sure if the target system has something like .NET installed on it. Plenty of Microsoft’s product CDs use HTAs for their AutoRun launchers.
It transpires that Mozilla are also now getting in on the act with Prism, which makes sense as Firefox itself is a kind of an HTML application. Go to Program FilesMozilla Firefoxchrome crack open the browser.jar file with a ZIP utility and you’re presented with a bunch of markup (XUL rather than HTML), CSS and JavaScript.
AIR or HTAs give you HTML as your control surface which is so much more flexible than Windows Forms and without the learning curve and heavyweight runtime requirements of WPF. For the application logic: JavaScript is a great, flexible language which when coupled with something like jQuery is incredibly powerful for doing UI manipulation.
It seems that AIR really picks up from where HTAs left off with the added promise of cross-platform compatibility. The Adobe AIR runtime is impressively small (10MB), fast and easy to install. (This highlights a bugbear I have with the .NET Framework these days: it really needs to go on a diet, or become less monolithic. The .NET 3.5 runtime is over 100MB in total, whereas .NET 1.x was about 20MB.)
Anyway I digress. If you want to dig into creating AIR apps in more detail, Jonathan Snook has just written seasonal overview, which goes into topics such as data storage, file system access and application packaging.
Duncan Smart's Blog 
Nice article. I have done some pretty expansive programs (if you want to call them that) using HTML Applications in the past but was not aware of the ability to contain them all in an EXE or DLL. Web documentation is kind of all over the place on that subject. Do you know where you may have found info on that?
Will have to check out using AIR, sounds promising.