Cocoa in a Nutshell

Memory Management

To properly manage memory, Cocoa provides a reference counting mechanism, supported by the NSObject and NSAutoreleasePool classes. As its name suggests, reference counting maintains a count of how many references there are to an object—indicating how many other objects are interested in keeping the object around. Reference counting is not automatic; the compiler has no way to determine an object’s lifetime. Therefore, the following NSObject reference counting methods must be called to indicate the level of interest in an object to the memory management system:

retain

Increments the object’s reference count by 1. When you want to register interest in an object that you did not create or copy, indicate interest in it by calling this method.

release

Decrements the object’s reference count by 1. This message is sent to objects created with the alloc method or sent a retain message when you are no longer interested in using them. If this causes the retain count to reach 0, the runtime deallocates the object.

autorelease

Adds the object to the current autorelease pool . This allows you to release your interest in an object without immediately causing the retain count to reach 0. When the autorelease pool is itself released, it sends the release message to every object it contains. This is most useful when you want to pass the object to another object as a return value and won’t have the opportunity to release the object later by yourself.

The following set of rules will ...