Objective-C Fundamentals

Subclassing
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the only class you can subclass: any class in Objective-C can be extended by subclassing.
NSObject is explored in more detail later in this chapter.
6.1.1 What is subclassing?
Subclassing is the act of taking a class, with all of its methods and instance variables,
and adding to it. A classic example of subclassing logic is used in taxonomy, when classifying
species. A human is a mammal; a tiger is a mammal as well. Tigers and humans
can both be thought of as subclasses of the mammal class because they share some
common features:
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■
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Warm blood
Vertebrae
Hair
While tigers and humans don’t share a ton of similarities, they do share these features
and, as a result, they’re both subclasses of the mammal class. This is exactly the idea
that’s applied when subclassing in an object-oriented programming language. You
subclass something when you want to keep everything about it and add to it. Let’s go
through an example of subclassing in Objective-C.
You’ll create a small iPhone application that utilizes some simple subclassing. First,
you create a class called Person that describes some general attributes of a person:
name, age, and gender.
1 Open Xcode and create a new View-based iPhone application called PersonClass.
2 Click File > New File and create a new Objective-C Class called Person as a subclass
of NSObject.
3 Fill in Person.h with the content of the following listing.
Listing 6.1
Creating the Person class
#import
typedef enum {
Male, Female
} Gender;
@interface Person : NSObject {
NSString *name;
NSNumber *age;
Gender gender;
}
- (id)initWithName:(NSString *)_name;
- (id)initWithAge:(NSNumber *)_age;
- (id)initWithGender:(Gender)_gender;
- (id)initWithName:(NSString *)_name
age:(NSNumber *)_age
gender:(Gender)_gender;
@end