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Developing Portable Mobile Web Applications
What if you could write iPhone and iPad applications on Linux? And, what if those applications also ran on Android phones? Well, you can, by writing your application as a portable mobile Web application. Take advantage of HTML5 and JavaScript libraries to write rich Web applications that users can't tell from native applications. You even can have them install from iTunes and Android Market. Plus,
If you want to package a Web application for distribution on iTunes or Android Market, one way is to use the appropriate SDK and write a small wrapper application. The application creates a browser Intent (Android) or a UIWebView (iPhone) and gives it the location of index.html. We don't have room to go into the SDKs here, but the applications are literally a few lines of code.
Or, for iTunes, you can let a package like PhoneGap do the work for you. You still need the iPhone SDK, so you have to create the package on a Mac, but PhoneGap makes the process simpler. Once it's created, you can upload it to iTunes like any other iPhone app.
If you don't care about iTunes or Android Market, there's another way—package your application as an HTML5 Offline Application. Listing 3 is a manifest file, webnotes.manifest, that you put in the home directory of your application. You also need to add an attribute to the <html> element in index.html:
manifest="webnotes.manifest"
One more thing—if you're serving the files from an Apache Web server, the .htaccess file in your Web directory needs a line like:
AddType text/cache-manifest .manifest
This tells Apache to serve .manifest files with the correct MIME type. When a user first goes to the Web site, the server will download the files listed in the manifest and keep them on the device. On subsequent visits, the file will be reloaded if the manifest changes—even if the change is in a comment field.
On Apple devices, when users go to your Web site, they can touch + at the bottom of the browser to put an icon for that URL on their homescreen (remember that .icon attribute when we initialized jQTouch?). If you've created an off-line application, it loads and executes from local storage, much like a native application.
We defined Webnotes to be similar to an example application that comes with the Android SDK called NotePad. See Table 1 for a comparison of lines of code.
Table 1. Comparing Lines of Code
| NotePad | Webnotes | |
|---|---|---|
| Java | 672 | |
| XML | 50 | |
| HTML | 62 | |
| JavaScript | 121 | |
| Source Lines | 722 | 183 |
If the effort to write a line of code is about the same in any language, it would take about a fourth of the time to write the application as a Web application—and it runs on most mobile WebKit-based browsers. That's worth considering as you plan your next mobile application development.
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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.
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Comments
Android compatibility.
I'm getting my feet wet with mobile development and am trying to get this working. I'm developing on an HTC Droid Eris with Android 2.1. All I'm getting is a black screen. Any one have any ideas if it should work? Or where I should be looking?
"well documented elsewhere"
"Installation of the tools is well documented elsewhere. The Resources section for this article gives pointers to the download URLs."
The resources indeed gives the pointers to the download URLs.
Is there also a link available for "well documented elsewhere"?
Is there also a pointer to the installation of the tools?
Regards,
M. Moon