Programming iOS 6, 3rd Edition

Memory Management

It comes as a surprise to many beginning Cocoa coders that the programmer has an important role to play in the explicit management of memory. What’s more, managing memory incorrectly is probably the most frequent cause of crashes — or, inversely, of memory leakage, whereby your app’s use of memory increases relentlessly until, in the worst-case scenario, there’s no memory left.

Fortunately, if your app uses ARC, your explicit memory management responsibilities can be greatly reduced, which is a tremendous relief, as you are far less likely to make a mistake, and more of your time is liberated to concentrate on what your app actually does instead of dealing with memory management concerns. But even with ARC it is still possible to make a memory management mistake (I speak from personal experience), so you still need to understand Cocoa memory management, so that you know what ARC is doing for you, and so that you know how to interface with ARC in situations where it needs your assistance. Do not, therefore, suppose that you don’t need to read this section on the grounds that you’re going to be using ARC.

Principles of Cocoa Memory Management

The reason why memory must be managed at all is that object references are pointers. As I explained in Chapter 1, the pointers themselves are simple C values (basically they are just integers) and are managed automatically, whereas what an object pointer points to is a hunk of memory that must explicitly be set aside when the ...