objective-C中分类的实现

分类机制允许向一个类文件中添加新的方法声明，它不需要使用子类机制，并且在类实现的文件中的同一个名字下定义这些方法。

#import “ClassName.h”

@interface ClassName (CategoryName)

@end

Vector.h 代码
#import <Foundation/Foundation.h>

@interface Vector : NSObject
{
    double _vec1;
    double _vec2;
}
@property (nonatomic,assign) double vec1;
@property (nonatomic,assign) double vec2;
-(Vector *)add:(Vector *)v;
-(void)setVec1:(double)vec1 AndVec2:(double)vec2;
-(void)print;
@end

Vector.m 代码

#import "Vector.h"

@implementation Vector
@synthesize vec1=_vec1;
@synthesize vec2=_vec2;
-(void)print
{
    NSLog(@"v1 value is %f,v2 value is %f",self.vec1,self.vec2);
}

-(void)setVec1:(double)vec1 AndVec2:(double)vec2
{
    self.vec1=vec1;
    self.vec2=vec2;
}
-(Vector*)add:(Vector *)v
{
    Vector *vector=[[Vector alloc]init];
    vector.vec1=v.vec1+self.vec1;
    vector.vec2=v.vec2+self.vec2;
    return vector;
}

@end

vector+sub.h 代码

#import <Foundation/Foundation.h>
#import "Vector.h"
@interface Vector(sub)

-(Vector *)sub:(Vector *)v;
@end

vector+sub.m code

#import "Vector+sub.h"

@implementation Vector (sub)
-(Vector *)sub:(Vector *)v
{
    Vector *temp=[[Vector alloc ]init];
    temp.vec1=self.vec1-v.vec1;
    temp.vec2=self.vec2-v.vec2;
    return temp;
}

@end

main code:

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        Vector *test1=[[Vector alloc]init];
        [test1 setVec1:2.2 AndVec2:3.4];
        [test1 print];
        Vector *test2=[[Vector alloc]init];
        [test2 setVec1:1.1 AndVec2:1.2];
        Vector *ret=[test1 sub:test2];
        [ret print];
        [test1 release];
        [test2 release];
        
    }
    
    return 0;
}

result:

2013-05-06 17:38:34.751 Access[2057:303] v1 value is 2.200000,v2 value is 3.400000
2013-05-06 17:38:34.753 Access[2057:303] v1 value is 1.100000,v2 value is 2.200000

分类是C++没有的概念，分类的使用是通过Objective-C的动态绑定实现，通过分类能够实现比继承更好的效果