[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