Mac OS X Leopard - ARCAism

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CHAPTER 26 MAC OS X DEVELOPMENT: OBJECTIVE-C
Object-Oriented Programming
with Objective-C
Projects written with procedural languages, such as C, become very difficult to understand as
they grow larger. Object-oriented programming languages, such as Objective-C, offer a way to
organize code into structured units called classes. From a C perspective, a class is like a struct, a
typedef, and a library of functions all rolled into one. An object is an individual instance of
a class.
Other than that broad review, the tenets of object-oriented programming are beyond the
scope of this book. Fortunately, it’s something most developers should already be familiar with.
What’s important to the topic at hand are the ways Objective-C implements those tenets and the
advantages Objective-C offers, compared to other object-oriented languages.
Declaring an Interface
Let’s look at the header of a simple Objective-C class:
#import
@interface BMPerson : NSObject {
NSString *name;
NSUInteger age;
}
+ (BMPerson *)personWithName:(NSString *)aName age:(NSUInteger)anAge;
- (NSString *)name;
- (void)setName:(NSString *)aName;
- (NSUInteger)age;
- (void)setAge:(NSUInteger)anAge;
@end
The first thing you need to do is import your application frameworks. For convenience, you
can just import the entirety of Cocoa:
#import
The #import directive is an improved version of C’s #include directive that will add the
header files only if they have not already been defined.
You begin the interface with the declaration @interface, name the class BMPerson, and use the
: operator to set its superclass to NSObject:
@interface BMPerson : NSObject {
NOTE Objective-C does not use namespaces, so class names start with a (usually two-letter)
prefix to reduce the chance of overlap. Since we’re going beyond the manual, we’ll go with BM,
but you should choose something appropriate, such as your initials, the initials of your company,
or something germaine to your project.
The brace opens the composition section, where we declare instance variables, also known
as ivars. We can use object types by declaring a pointer to the type.
NSString *name;