Introduction

When Apple introduced the iPhone Software Development Kit (SDK) in 2008, the iPhone and iPod touch suddenly became the handheld computers they were meant to be. Interest in the SDK exceeded Apple's expectations — in fact, Apple's servers supplying the beta for the first SDK download were overwhelmed.

Since then, the App Store has grown to become the repository of over 140,000 applications, which collectively are driving innovation beyond the reach of other mobile devices. The success of the App Store — over three billion downloads — has turned the iPhone into the premier mobile device for publishing software. All the leading mobile applications typically appear on the iPhone first, and as a reader of this book, you may be creating the next one.

As I continue to explore the iPhone as a new platform, I keep finding more possibilities for applications that never existed before. The iPhone or iPod touch is a mobile computer, but not like a mobile desktop. Its hardware and software make it possible to wander the world, or your own neighborhood, and stay connected to whomever and whatever you want to. It enables a new class of here-and-now applications that give you access to content-rich services and let you view information about what's going on around you and where you are, and interact with those services or with others on the Internet.

One of the hallmarks of a great iPhone application is that it leverages the iPhone's unique hardware, especially its ability to know where ...

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