Thanks to mobile phones, we have moved from virtually no one having access to information to virtually everyone having access to the vast resources of the Web. This is arguably the most important achievement of our generation. Despite its overarching importance, mobile computing is in its infancy. Technical, financial, and political forces have created platform fragmentation like never before, and it's going to get worse before it gets better.

Developers who need to engage large and diverse groups of people are faced with a seemingly impossible challenge: "How do we implement our mobile vision in a way that is feasible, affordable, and reaches the greatest number of participants?" In many cases, the answer is web technologies. The combination of advances in HTML5 and mobile devices has created an environment in which even novice developers can build mobile apps that improve people's lives on a global scale.

Google's Android operating system is a compelling addition to the mobile computing space. In true Google fashion, the platform is open, free, and highly interoperable. The development tools are full-featured and powerful, if a bit geeky, and run on a variety of platforms.

Carriers and handset manufacturers have jumped on the Android bandwagon. The market is beginning to flood with Android devices of all shapes and sizes. This is a double-edged sword for developers. On one hand, more devices means a bigger market. On the other hand, more devices means more fragmentation. As with the fragmentation in the general mobile market, fragmentation on Android can often be addressed by building apps with HTML, CSS, and JavaScript.

I'm the first to admit that not all apps are a good fit for development with web technologies. That said, I see a lot of apps written with native code that could have just as easily been done with HTML. When speaking to developers who aren't sure which approach to take, I say this:

If you can build your app with HTML, CSS, and JavaScript, you probably should.

Using open source, standards-based web technologies gives you the greatest flexibility, the broadest reach, and the lowest cost. You can easily release it as a web app, then debug and test it under load with thousands of real users. Once you are ready to rock, you can use PhoneGap to convert your web app to a native Android app, add a few device-specific features if you like, and submit to the Android Market—or offer it for download from your website. Sounds good, right?

I'm going to assume you have some basic experience reading and writing HTML, CSS, and JavaScript (jQuery in particular). Chapter 5 includes some basic SQL code, so a passing familiarity with SQL syntax would be helpful but is not required.

This book avoids the Android SDK wherever possible. All you need to follow along with the vast majority of examples is a text editor and the most recent version of Google Chrome (a cutting-edge web browser that's available for both Mac and Windows at You do need to have the Android SDK for the Phone-Gap material in Chapter 7, where I explain how to convert your web app into a native app that you can submit to the Android Market.

The following typographical conventions are used in this book: Italic

Indicates new terms, URLs, email addresses, filenames, and file extensions. Constant width

Used for program listings, as well as within paragraphs to refer to program elements such as variable or function names, databases, data types, environment variables, statements, and keywords. Constant width bold

Shows commands or other text that should be typed literally by the user.

Constant width italic

Shows text that should be replaced with user-supplied values or by values determined by context.

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