1、类别(category)和扩展

类别:OC动态特征许使用类别添加新的方法，不需要创建子类

扩展：和类别相似，扩展相对于匿名类别

2、使用格式

@interface 已有类(类别名)…@end

@implmentaion 已有类(类别名)…@end

@imterface 也有类()
{实例变量
}
//方法...@end

3、哪些功能

1)、给一个现成的类增加类别，然后实现其方法

2)、模块化设计

3)、调用私有方法（没有在接口部分定义而是在类实现部分定义的方法相对于私有方法，不许调用），通过定义向前引用，实现对私有方法调用

4、测试类别Demo

#ifndef NSNumber_fk_h
#define NSNumber_fk_h
#import <Foundation/Foundation.h>
@interface NSNumber(fk)
-(NSNumber *)add:(double)num2;
-(NSNumber *)sub:(double)num2;
@end#endif /* NSNumber_fk_h */

NSNumer+fk.m

#import <Foundation/Foundation.h>
#import "NSNumber+fk.h"@implementation NSNumber(fk)
-(NSNumber *)add:(double)num2
{return [NSNumber numberWithDouble:([self doubleValue] + num2)];
}
-(NSNumber *)sub:(double)num2
{return [NSNumber numberWithDouble:([self doubleValue] - num2)];
}
@end

MyApple.h

#import <Foundation/Foundation.h>#ifndef MyApple_h
#define MyApple_h
@interface MyApple : NSObject
@property (nonatomic, assign) double weight;
@property (nonatomic, copy) NSString *color;
//java方法构造方法一般没有返回，oc这里需要返回id,记住
-(id)initWithColor:(NSString *)color weight:(double)weight;
@end

MyApple.m

#import "MyApple.h"
//#import "MyApple+fk.h"#import <Foundation/Foundation.h>
@implementation MyApple
@synthesize color = _color;
@synthesize weight = _weight;
-(id)initWithColor:(NSString *)color weight:(double)weight
{if (self = [super init]){self.color = color;self.weight = weight;}return self;
}-(NSString *) description
{return [NSString stringWithFormat:@"<MyApple[color=%@, weight=%g]>", self.color, self.weight];
}
-(void)test
{NSLog(@"this is test method");
}
@end

MyApple+fk.h

#import "MyApple.h"#ifndef MyApple_fk_h
#define MyApple_fk_h
@interface MyApple(fk)
-(void)test;
@end
#endif /* MyApple_fk_h */

main.h

#import "MyApple.h"
#import "NSNumber+fk.h"
#import "MyApple+fk.h"int main(int argc, char * argv[]) {@autoreleasepool {NSNumber *num = [NSNumber numberWithDouble:3.5];NSLog(@"3.5 - 2 is %@", [num sub:2]);NSLog(@"3.5 + 2 is %@", [num add:2]);MyApple *apple = [[MyApple alloc] initWithColor:@"red" weight:5.6];NSLog(@"%@", apple);//No visible @interface for 'MyApple' declares the selector 'test'[apple test];}
}

5、运行类别结果

3.5 - 2 is 1.5
3.5 + 2 is 5.5
<MyApple[color=red, weight=5.6]>
this is test method

#ifndef Car_h
#define Car_h#import <Foundation/Foundation.h>
@interface Car : NSObject
@property (nonatomic, copy) NSString *brand;
@property (nonatomic, copy) NSString *model;
-(void)drive;
@end
#endif /* Car_h */

#import "Car.h"
#ifndef Car_drive_h
#define Car_drive_h@interface Car()
@property (nonatomic, copy) NSString *color;
-(void)drive:(NSString *)owner;
@end#endif /* Car_drive_h */

#import <Foundation/Foundation.h>
#import "Car+drive.h"@implementation Car
@synthesize brand;
@synthesize model;
@synthesize color;-(void)drive
{NSLog(@"%@汽车正在路上奔驰",self);
}
-(void)drive:(NSString *)owner
{NSLog(@"%@正驾驶%@汽车在路上奔驰", owner, self);
}
-(NSString *)description
{return [NSString stringWithFormat:@"<Car [brand=%@, model=%@, color=%@]>", self.brand, self.model, self.color];
}
@end

#import "Car+drive.h"
int main(int argc, char * argv[]) {@autoreleasepool {Car *car = [Car new];car.brand = @"奔驰";car.model = @"S300";car.color = @"red";[car drive];[car drive:@"chenyu"];}
}

<Car [brand=奔驰, model=S300, color=red]>汽车正在路上奔驰
chenyu正驾驶<Car [brand=奔驰, model=S300, color=red]>汽车在路上奔驰