Objective C 类别和继承

Objective-C 是一种面向对象的编程语言，它支持类别（category）和继承（inheritance）这两个重要的特性。类别是一种在已有类的基础上扩展功能的方式，而继承则是一种从已有类派生出新类的方式。在本文中，我们将详细介绍 Objective-C 中的类别和继承，并且通过案例代码来说明它们的使用。

objective-c
// NSString+Length.h
#import 
@interface NSString (Length)
- (NSUInteger)length;
@end
// NSString+Length.m
#import "NSString+Length.h"
@implementation NSString (Length)
- (NSUInteger)length {
    return [self length];
}
@end

objective-c
#import "NSString+Length.h"
NSString *str = @"Hello, world!";
NSUInteger len = [str length];
NSLog(@"The length of the string is %lu", len);

objective-c
// Animal.h
#import 
@interface Animal : NSObject
@property (nonatomic, copy) NSString *name;
- (void)speak;
@end
// Animal.m
#import "Animal.h"
@implementation Animal
- (void)speak {
    NSLog(@"I am an animal.");
}
@end
// Dog.h
#import "Animal.h"
@interface Dog : Animal
@property (nonatomic, assign) NSUInteger age;
- (void)bark;
@end
// Dog.m
#import "Dog.h"
@implementation Dog
- (void)bark {
    NSLog(@"Woof Woof!");
}
@end

objective-c
Animal *animal = [[Animal alloc] init];
animal.name = @"Tom";
[animal speak];
Dog *dog = [[Dog alloc] init];
dog.name = @"Max";
dog.age = 3;
[dog speak];
[dog bark];