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. It’s an independent creature, a leaner, meaner, smarter Cocoa. I could praise Cocoa Touch’s deliberate use of systematization (and its healthy respect for Occam’s Razor) through numerous examples. Where Mac OS X’s animation layers are glommed onto views as a kind of afterthought, a Cocoa Touch view always has an animation layer counterpart.
