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

AddressCard.h

 #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

AddressCard.m

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

@end

AddressCard(category)分类声明文件

 #import "AddressCardCategory.h"

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

 @end

AddressCard(Category)实现文件

 #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 ;
 }

main 函数如下：

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