Learning the iOS 4 SDK for JavaScript Programmers

Enumerated Types

In your tour of Cocoa Touch frameworks, you will encounter many collections of values known as enumerated types. Defined in C with the enum statement, the construction is a collection of convenient names representing integer values. It’s easier to show you than explain it.

You are probably familiar with the Maps app, which lets you select from three different map styles: standard, satellite, and hybrid. If you add a map view to your app, your code can change the style by sending the setMapType: message to an instance of MKMapView. Acceptable values are integers: 0, 1, and 2 to denote standard, satellite, and hybrid, respectively. To help make your code more readable, these values have been assigned to names that act as constants for their designated data type (i.e., they can’t be used in other places). Because the values are all related, they are grouped into an enumerated list and assigned a type definition. The three map style values are defined in the mapping framework as follows:

enum {
   MKMapTypeStandard,
   MKMapTypeSatellite,
   MKMapTypeHybrid
};
typedef NSUInteger MKMapType;

By default, an enum type assigns integer values (beginning with 0) to the constant names in the group. It is also possible to assign explicit numbers to each constant name or assign a different starting point for the items by assigning a nonzero value to one item (in which case, subsequent items have incremental integer values). For your coding, you don’t concern yourself with the integer values, ...