iOS 6 Programming Cookbook

1.23. Allocating and Making Use of Arrays

Problem

You want to store a series of objects into another object for later use.

Solution

Use NSArray and NSMutableArray classes to store objects into arrays that are fixed and that you can change, respectively.

Discussion

An object of type NSArray or any of its subclasses has the capability to store n number of other objects, where n will be determined by the runtime and is influenced by how much memory is available at the time. These objects can then be accessed using their index. For instance, let’s say you have 10 pairs of socks. Now imagine placing them all on a flat surface from left to right and calling them socks 1, socks 2, socks 3, and so on. So the leftmost pair of socks is now addressed as socks 1, the pair next to it is called socks 2, and the rightmost pair is called socks 10. Isn’t that easier than saying something like “the blue socks next to my red socks”? That’s exactly what arrays do: they make arranging items much easier.

Note

You can place any object of type NSObject or any of its subclasses into an array of type NSArray (or subclasses of that type). An array can contain a mix of different types of objects. Not all objects have to be of the same type. In other words, you can have one array with strings, numbers, dictionaries, or even other arrays inside it. Arrays can contain any object as long as those objects can be wrapped in the id data type wrapper.

The primary difference between NSArray and NSMutableArray is that a mutable ...