[置顶] Objective-C,/,ios,/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）

 1 #import <Foundation/Foundation.h>
 2
 3 @interface AddressCard : NSObject<NSCoding>{
 4     NSString* name;
 5     NSString* email;
 6 }
 7 @property (nonatomic,retain)NSString* name;
 8 @property (nonatomic,retain)NSString* email;
 9 -(id)initWithName:(NSString*)_name andEmail:(NSString*)_email;
10
11 @end

 1 #import "AddressCard.h"
 2
 3 @implementation AddressCard
 4 @synthesize name,email;
 5 -(id)initWithName:(NSString*)_name andEmail:(NSString*)_email{
 6     if(self= [super init])
 7     {
 8         self.name=_name;
 9         self.email=_email;
10     }
11     return self;
12 }
13 -(void)encodeWithCoder:(NSCoder *)aCoder{
14     [aCoder encodeObject:name forKey:@"_name"];
15     [aCoder encodeObject:email forKey:@"_email"];
16 }
17
18 -(id)initWithCoder:(NSCoder*)aDecoder{
19     if(self=[super init])
20     {
21         self.name=[aDecoder decodeObjectForKey:@"_name"];
22         self.email=[aDecoder decodeObjectForKey:@"_email"];
23     }
24     return self;
25 }
26 -(void)dealloc{
27     [name release];
28     [email release];
29     [super dealloc];
30 }
31 @end

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

@end

1 #import "AddressCardCategory.h"
2
3 @implementation AddressCard(Category)
4 -(void)uppercaseName{
5     self.name= [name uppercaseString];
6 }
7
8 @end

 1 #import <Foundation/Foundation.h>
 2 #import "AddressCardCategory.h"
 3 int main (int argc, const char * argv[])
 4 {
 5
 6     @autoreleasepool {
 7         AddressCard* card1=[[AddressCard alloc]initWithName:@"shou" andEmail:@"abc@126.com"];
 8         [NSKeyedArchiver archiveRootObject:card1 toFile:@"/tmp/AddressCard.txt"];
 9         AddressCard* card4=[NSKeyedUnarchiver unarchiveObjectWithFile:@"/tmp/AddressCard.txt"];
10         NSLog(@"card 4 %@ ,%@",card4.name,card4.email);
11         [card4 uppercaseName];
12          NSLog(@"card 4 %@ ,%@",card4.name,card4.email);
13         [card1 release];
14         //[card4 release];
15
16
17     }
18     return 0;
19 }

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