Objective-C /iphone开发基础：分类（category,又称类别）

在c++中我们可以多继承来实现代码复用和封装使程序更加简练。在objective-c中只能单继承，不能多继承，那么除了协议protocol之外，我们可以实现类似多继承的一个方法就是，分类（category,又称类别）。类别可以不修改原来的类（父类），和派生类的情况下，为原有的类增加新的方法，但是分类不能增加实例变量。

格式（format）：

@interface class_name(category_name)<protocol,....>

method _declaration;

....

@end

@implementation class_name(category_name)

method_implementation;

...

@end

新建一个AddressCard类，然后再新建一个文件 AddressCardCategory 用来声明和实现分类（category）

#import <Foundation/Foundation.h>

@interface AddressCard : NSObject<NSCoding>{
    NSString* name;
    NSString* email;
}
@property (nonatomic,retain)NSString* name;
@property (nonatomic,retain)NSString* email;
-(id)initWithName:(NSString*)_name andEmail:(NSString*)_email;

@end

 

#import "AddressCard.h"

@implementation AddressCard
@synthesize name,email;
-(id)initWithName:(NSString*)_name andEmail:(NSString*)_email{
    if(self= [super init])
    {
        self.name=_name;
        self.email=_email;
    }
    return self;
}
-(void)encodeWithCoder:(NSCoder *)aCoder{
    [aCoder encodeObject:name forKey:@"_name"];
    [aCoder encodeObject:email forKey:@"_email"];
}

-(id)initWithCoder:(NSCoder*)aDecoder{
    if(self=[super init])
    {
        self.name=[aDecoder decodeObjectForKey:@"_name"];
        self.email=[aDecoder decodeObjectForKey:@"_email"];
    }
    return self;
}
-(void)dealloc{
    [name release];
    [email release];
    [super dealloc];
}
@end

 

#import <Foundation/Foundation.h>
#import "AddressCard.h"
@interface AddressCard(category)
-(void)uppercaseName;

@end

 

#import "AddressCardCategory.h"

@implementation AddressCard(Category)
-(void)uppercaseName{
    self.name= [name uppercaseString];
}

@end

#import <Foundation/Foundation.h>
#import "AddressCardCategory.h"
int main (int argc, const char * argv[])
{

    @autoreleasepool {
        AddressCard* card1=[[AddressCard alloc]initWithName:@"shou" andEmail:@"abc@126.com"];
        [NSKeyedArchiver archiveRootObject:card1 toFile:@"/tmp/AddressCard.txt"];
        AddressCard* card4=[NSKeyedUnarchiver unarchiveObjectWithFile:@"/tmp/AddressCard.txt"];
        NSLog(@"card 4 %@ ,%@",card4.name,card4.email);
        [card4 uppercaseName];
         NSLog(@"card 4 %@ ,%@",card4.name,card4.email);
        [card1 release];
        //[card4 release];
        
        
    }
    return 0;
}

执行结果：

2013-08-20 17:12:04.751 AddressCard[1079:707] card 4 shou ,abc@126.com
2013-08-20 17:12:04.758 AddressCard[1079:707] card 4 SHOU ,abc@126.com