[原创]obj-c编程16:键值编码(KVC)

原文链接:obj-c编程16:键值编码(KVC)

 

我们可以借助obj-c中的键值编码(以后简称KVC,Key-Value Coding)来存取类的属性,通过指定所要访问的属性名字符串标示符,可以使用存取器方法来获取或设置类的属性。下面的例子,借助于KVC的功能读取和设置了类Son实例的属性i:

 1 #import <Foundation/Foundation.h>
 2 
 3 #define msg(...) NSLog(__VA_ARGS__)
 4 #define mki(x) [NSNumber numberWithInt:x]
 5 
 6 @interface Son:NSObject{
 7     NSArray *ary;
 8     NSNumber *i;
 9 }
10     @property NSArray *ary;
11     @property NSNumber *i;
12 @end
13 
14 @implementation Son
15     @synthesize ary,i;
16 
17     -(id)init{
18         return [self init:0];
19     }
20 
21     -(id)init:(int)i_v{
22         self = [super init];
23         if(self){
24             ary = [NSArray arrayWithObjects:mki(1),mki(2),mki(10),\
25                 mki(100),nil];
26             i = [NSNumber numberWithInt:i_v];
27         }
28         return self;
29     }
30 @end
31 
32 int main(int argc,char *argv[])
33 {
34     @autoreleasepool{
35         Son *son = [[Son alloc] init];
36         [son setValue:mki(1001) forKey:@"i"];
37         msg(@"%@",[son valueForKey:@"i"]);
38         msg(@"%@",[son valueForKeyPath:@"ary.@count"]);

运行结果如下:

apple@kissAir: objc_src$clang -fobjc-arc -framework Foundation k.m -o k

apple@kissAir: objc_src$./k

2014-07-06 15:51:56.098 k[1386:507] 1001

 

KVC其中有KeyPath的概念,比如类Baba中有一个属性名为son,其是Son的对象;而类Son中也有属性NSString name,这时我们可以使用KeyPath的语法,像遍历树一样找到最终的属性name:

[baba valueForKeyPath:@"son.name"];

[baba setValue:@"tom" forKeyPath:@"son.name"];

除了遍历对象关系以外,我们还可以访问一些操作对象集合的函数,比如求平均数等等:

下面实际看一个例子

 1 #import <Foundation/Foundation.h>
 2 
 3 #define msg(...) NSLog(__VA_ARGS__)
 4 #define mki(x) [NSNumber numberWithInt:x]
 5 
 6 @interface Son:NSObject{
 7     NSArray *ary;
 8     NSNumber *i;
 9 }
10     @property NSArray *ary;
11     @property NSNumber *i;
12 @end
13 
14 @implementation Son
15     @synthesize ary,i;
16 
17     -(id)init{
18         return [self init:0];
19     }
20 
21     -(id)init:(int)i_v{
22         self = [super init];
23         if(self){
24             ary = [NSArray arrayWithObjects:mki(1),mki(2),mki(10),\
25                 mki(100),nil];
26             i = [NSNumber numberWithInt:i_v];
27         }
28         return self;
29     }
30 @end
31 
32 int main(int argc,char *argv[])
33 {
34     @autoreleasepool{
35         Son *son = [[Son alloc] init];
36         [son setValue:mki(1001) forKey:@"i"];
37         msg(@"%@",[son valueForKey:@"i"]);
38         msg(@"%@",[son valueForKeyPath:@"ary.@count"]);
39 
40         Son *son0 = [[Son alloc] init:11];
41         Son *son1 = [[Son alloc] init:200];
42         Son *son2 = [[Son alloc] init:25];
43 
44         NSArray *ary = [NSArray arrayWithObjects:son,son0,son1,son2,nil];
45         msg(@"avg:%@",[ary valueForKeyPath:@"@avg.i"]);
46         msg(@"sum:%@",[ary valueForKeyPath:@"@sum.i"]);
47 
48     }
49     return 0;
50 }

运行结果如下:

apple@kissAir: objc_src$./k

2014-07-06 15:51:56.098 k[1386:507] 1001

2014-07-06 15:51:56.100 k[1386:507] 4

2014-07-06 15:51:56.100 k[1386:507] avg:309.25

2014-07-06 15:51:56.101 k[1386:507] sum:1237

 

posted on 2014-07-07 10:40  大熊猫侯佩  阅读(303)  评论(0编辑  收藏  举报

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