Neuburg - Programming iOS 4

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With the advent of version 2 of the iPhone system, Apple proved they could do a remarkable thing adapt their existing Cocoa computer application programming framework to make applications for a touch-based device with limited memory and speed and a dauntingly tiny display. The resulting Cocoa Touch framework, in fact, turned out to be in many ways better than the original Cocoa.

A programming framework has a kind of personality, an overall flavor that provides an insight into the goals and mindset of those who created it. When I first encountered Cocoa Touch, my assessment of its personality was: Wow, the people who wrote this are really clever! On the one hand, the number of built-in interface widgets was severely and deliberately limited; on the other hand, the power and flexibility of some of those widgets, especially such things as UITableView, was greatly enhanced over their Mac OS X counterparts. Even more important, Apple created a particularly brilliant way (UIViewController) to help the programmer make entire blocks of interface come and go and supplant one another in a controlled, hierarchical manner, thus allowing that tiny iPhone display to unfold virtually into multiple interface worlds within a single app without the user becoming lost or confused.

Even more impressive, Apple took the opportunity to recreate and rationalize Cocoa from the ground up as Cocoa Touch. Cocoa itself is very old, having begun life as NeXTStep before Mac OS X even existed. It has grown by accretion and with a certain conservatism in order to maintain something like backward compatibility. With Cocoa Touch, on the other hand, Apple had the opportunity to throw out the baby with the bath water, and they seized this opportunity with both hands.

So, although Cocoa Touch is conceptually based on Mac OS X Cocoa, it is very clearly not Mac OS X Cocoa, nor is it limited or defined by Mac OS X Cocoa. Its an independent creature, a leaner, meaner, smarter Cocoa. I could praise Cocoa Touchs deliberate use of systematization (and its healthy respect for Occams Razor) through numerous examples. Where Mac OS Xs animation layers are glommed onto views as a kind of afterthought, a Cocoa Touch view always has an animation layer counterpart. Memory management policies, such as how top-level objects are managed when a nib loads, are simplified and clarified. And so on.

At the same time, Cocoa Touch is still a form of Cocoa. It still requires a knowledge of Objective-C. It is not a scripting language; it is certainly not aimed at nonprogrammers, like HyperCards HyperTalk or Apples AppleScript. It is still huge and complicated. In fact, its rather difficult.

Meanwhile, Cocoa Touch itself evolves and changes. The iPhone System 2 matured into the iPhone System 3. Then there was a sudden sally in a new direction when the iPad introduced a larger screen and iPhone System 3.2. The iPhone 4 and its double-resolution Retina display also ran on a major system increment, now dubbed iOS 4. Every one of these changes has brought new complexities for the programmer to deal with. To give just one simple example, users rightly complained that switching between apps on the iPhone meant quitting one app and launching another. So Apple gave the iPhone 4 the power of multitasking; the user can switch away from an app and then return to it later to find it still running and in the state it was left previously. All well and good, but now programmers must scurry to make their apps compatible with multitasking, which is not at all trivial.

The popularity of the iPhone, with its largely free or very inexpensive apps, and the subsequent popularity of the iPad, have brought and will continue to bring into the fold many new programmers who see programming for these devices as worthwhile and doable, even though they may not have felt the same way about Mac OS X. Apples own annual WWDC developer conventions have reflected this trend, with their emphasis shifted from Mac OS X to iOS instruction.

The widespread eagerness to program iOS, however, though delightful on the one hand, has also fostered a certain tendency to try to run without first learning to walk. iOS gives the programmer mighty powers that can seem as limitless as imagination itself, but it also has fundamentals. I often see questions online from programmers who are evidently deep into the creation of some interesting app, but who are stymied in a way that reveals quite clearly that they are unfamiliar with the basics of the very world in which they are so happily cavorting.

It is this state of affairs that has motivated me to write this book, which is intended to ground the reader in the fundamentals of iOS. I love Cocoa and have long wished to write about it, but it is iOS and its popularity that has given me a proximate excuse to do so. Indeed, my working title was Fundamentals of Cocoa Touch Programming. Here I have attempted to marshal and expound, in what I hope is a pedagogically helpful and instructive yet ruthlessly Euclidean and logical order, the principles on which sound iOS programming rests, including a good basic knowledge of Objective-C (starting with C itself) and the nature of object-oriented programming, advice on the use of the tools, the full story on how Cocoa objects are instantiated, referred to, put in communication with one another, and managed over their lifetimes, and a survey of the primary interface widgets and other common tasks. My hope, as with my previous books, is that you will both read this book cover to cover (learning something new often enough to keep you turning the pages) and keep it by you as a handy reference.