What I ended up arriving at was the ability to load and render a HTML file with it's own resources imported such as CSS, Javascript and images. The real magic in Objective C is this:
NSURL *url = [NSURL fileURLWithPath:[ [ NSBundle mainBundle ] pathForResource: @"index" ofType:@"html" ]];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
[webView loadRequest:request];
What this is doing is creating a URL with a resource on the path called 'index' with the file extension 'html'. Build a request from this URL and pass the request into the instance of UIWebView.
From that point, as long as all of the resources that the index page requires are bundled into the project, you can load the page and have that actually be the application.
So that's all nice if you have a certain type of application which doesn't require any device interaction. For example, if you had a blog/news site and wanted to make it into an application, you could just get the content and display. You can also change a few settings in a file called info.plist to set the icon image and application name.
That template project is available on GitHub, http://github.com/robb1e/iWeb
However, if you want device interaction you'll need a richer framework, and that's where something like PhoneGap.com comes in. With the abstracted Javascript file that works for iPhone, Blackberry and Android, functions are available to get access to the contact list, audio playback and other device features.
To play an embedded audio resource for example, you can write the following Javascript, provided you've included the PhoneGap.js file.
new Media('beep.wav').play();
With both of these projects there is one caveat with Xcode in that it wants to compile Javascript files. You have to make sure you set those files as resources to copy, not to compile. This can be done in the target list on the left hand side.
To extend the idea of using standard web technologies whilst not building web sites, this next example uses Adobe's AIR run time and the HTML, CSS, Javascript and image from the first example. This is also available on GitHub: http://github.com/robb1e/AirWeb
By creating the application.xml file, you can tell Air to launch a file as the initial content and that will be rendered using it's WebKit engine.
<content>www/index.html</content>
To run the desktop app, install the Adobe AIR SDK then run the command:
adl application.xml
This launches the application in debug mode. To create an Air file, you need to compile using ADT.
This has shown that using the same technologies and languages you'd use to build a web page can be used for both mobile devices with and without device interaction and client applications that are installed on a computer.
There are other ways of achieving the same result using Apple's web namespace tags in the markup with HTML5 tricks like offline storage. There's also other libraries like jQTouch, so check out what else is around too.
The "write once, run anywhere" idea may just be coming into reality .
