Developing Portable Mobile Web Applications
Mobile applications for iPhone and Android smartphones are where the excitement is today in application development. There are plenty of customers (Canalys says there were almost 8 million Android phones and more than 25 million iPhones sold in 2009), and those users regularly load applications on their phones (AdMob says Android and iPhone users average around nine downloads a month, and iTouch users average around 12). The demand for mobile applications is hot.
How can a Linux developer tackle this market? Native applications for the iPhone must be developed with the Apple iPhone SDK, which runs only on Mac OS X. Android development is supported on Linux with the Android SDK, but ideally, you'd like to develop apps on Linux that run on both iPhone and Android.
Browser security prevented the storage of local data.
Users had to start the browser to use a Web app, which then didn't match the native UI.
HTML5 and related specifications add features like canvas, video, local storage, Web workers, off-line applications and geolocation to HTML, and WebKit is rapidly integrating these into the layout engine.
iUi: a small extensible library that mimics the iPhone user interface.
iWebKit: another framework for iPhone-style applications.
Android and iPhone both use WebKit as their layout engine, but there are still differences, partly due to the selection of different WebKit releases:
Android 1.6 (HTC G1) uses WebKit 525.20 and implements only Canvas, Canvas Text and Geolocation.
Android 2.1 (Motorola Droid) uses WebKit 530.17 and adds the rest of HTML5 (video, audio, local storage, Web Workers and off-line applications).
iPhone 3GS and iTouch use WebKit 528.16 and .18 and include all features except for Web Workers (multithreading).
iPad uses WebKit 531.21 and includes all features.
Developing Web applications for smartphones is pretty straightforward, but there are some things you need to know:
It's not like C: if you're used to developing Linux applications in C or C++ or Java or Perl, this is different. Web application development is a little closer to the Android development environment, where screen layouts are in XML files, and functionality is written in Java, but mostly, it's like Web development.
Native apps require native SDKs: if you want users to be able to load your application from iTunes and Android Market, you have to enable that with the appropriate SDKs. There are workarounds that I talk about later.
Rick Rogers has been a professional embedded developer for more than 30 years. Now specializing in mobile application software, when Rick isn't writing software for a living, he's writing books and magazine articles like this one.