iOS Programming: The Big Nerd Ranch Guide, Second Edition

Using Instances

An instance of a class (an object) has a life span: it is created, sent messages, and then destroyed when it is no longer needed.

Creating objects

To create an object, you send an alloc message to a class. In response, that class creates an object in memory and gives you a pointer to it. Creating an object looks like this:

N​S​M​u​t​a​b​l​e​A​r​r​a​y​ ​*​a​r​r​a​y​I​n​s​t​a​n​c​e​ ​=​ ​[​N​S​M​u​t​a​b​l​e​A​r​r​a​y​ ​a​l​l​o​c​]​;​

Here an instance of type NSMutableArray is created, and you are returned a pointer to it in the variable arrayInstance. When you have a pointer to an instance, you can send messages to it. The first message you always send to a newly allocated instance is an initialization message. Although sending ...