KVC –key value Coding，可以让我们通过键值编码的形式进行属性值的赋值

参考苹果官网的图。。

1.KVC

定义一个Person类

.h文件

   1:  #import <Foundation/Foundation.h>

   2:  

   3:  @interface Person : NSObject

   4:  {

   5:     NSString *name;

   6:  }

   7:   

   8:  @end

.m文件

   1:  #import "Person.h"

   2:   

   3:  @implementation Person

   4:   

   5:  @end

通过普通的获取属性的方法是无法对name进行赋值和取值操作的，这种情况可以通过KVC来进行设置和取值

   1:  - (void)viewDidLoad {

   2:      [super viewDidLoad];

   3:      // Do any additional setup after loading the view, typically from a nib.

   4:     Person  person=[[Person alloc]init];

   5:      [person setValue:@"keith" forKey:@"name"];

   6:      NSLog(@"name is %@",[person valueForKey:@"name"]);

   7:  }

赋值用setValue:forKey:

取值用 valueForKey:

2.键路径

如果类中包含其他的类怎么办呢，访问这个类的属性怎么办呢。可以使用setValue: forKeyPath: 和valueForKeyPath设置和获取

如定义一个car

.h文件

#import <Foundation/Foundation.h>

@interface Car : NSObject
{
    NSString *carname;
}
@end

将Person的.h改成

#import <Foundation/Foundation.h>
@class Car;
@interface Person : NSObject
{
    NSString *name;
    Car *hiscar;
}
-(id)init;
@end

.m为

#import "Person.h"
#import "Car.h"
@implementation Person
-(id)init{
    if (self=[super init]) {
        hiscar=[[Car alloc]init];
    }
    return self;
}
@end

这里实现了car的实例化，如果不这么做在键值编程时候hiscar因为没有初始化而出现无法赋值的情况

调用:

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    Person *person=[[Person alloc]init];
    [person setValue:@"keith" forKey:@"name"];

    [person setValue:@"QQ" forKeyPath:@"hiscar.carname"];
    NSLog(@"name is %@,hiscar is %@",[person valueForKey:@"name"],[person valueForKeyPath:@"hiscar.carname"]);
    
    /*或者这样*/
     Car *car=[[Car alloc]init];
     [car setValue:@"BeiKy" forKey:@"carname"];
     [person setValue:car forKey:@"hiscar"];
    NSLog(@"name is %@,hiscar is %@",[person valueForKey:@"name"],[person valueForKeyPath:@"hiscar.carname"]);

}

输出结果

2014-11-26 22:45:47.392 KVCtest[1031:25564] name is keith,hiscar is QQ
2014-11-26 22:45:47.394 KVCtest[1031:25564] name is keith,hiscar is BeiKy

3.类型封装和转换

再次修改Person.h文件

#import <Foundation/Foundation.h>
@class Car;
@interface Person : NSObject
{
    NSString *name;
    Car *hiscar;
    NSInteger age;//增加一个年龄类型是NSInteger
}
-(id)init;
@end

那么如何在设置的时候会发生什么呢？

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    Person *person=[[Person alloc]init];
    [person setValue:@"keith" forKey:@"name"];
    [person setValue:@"QQ" forKeyPath:@"hiscar.carname"];
    [person setValue:@"24" forKeyPath:@"age"];//为年龄赋值
    NSLog(@"name is %@, is %@ old ,hiscar is %@",[person valueForKey:@"name"],[person valueForKey:@"age"],[person valueForKeyPath:@"hiscar.carname"]);

}

结果是:

2014-11-26 22:56:08.873 KVCtest[1086:27956] name is keith, is 24 old ,hiscar is QQ

4.操作集合

在Person中添加一个otherPerson

#import <Foundation/Foundation.h>
@class Car;
@interface Person : NSObject
{
    NSString *name;
    Car *hiscar;
    NSInteger age;
    NSMutableArray *otherPerson;
}
-(id)init;
@end

属性.@sum.属性，还有@count,@avg,@max.@min

-(void)kvcCollection{
    Person *person=[[Person alloc]init];
    [person setValue:@"keith" forKey:@"name"];
    Person *person1=[[Person alloc]init];
    Person *person2=[[Person alloc]init];
    Person *person3=[[Person alloc]init];
    Person *person4=[[Person alloc]init];
    NSMutableArray *others=[[NSMutableArray alloc]initWithObjects:person1,person2,person3,person4, nil];
    NSInteger agenum=20;
    for (Person *p in others) {
        [self setage:p age:[[NSString alloc]initWithFormat:@"%ld",agenum++]];
    }
    [person setValue:others forKey:@"otherPerson"];
    NSLog(@"other's age is %@",[person valueForKeyPath:@"otherPerson.age"]);
    NSLog(@"the avg age is %@",[person valueForKeyPath:@"[email protected]"]);
    NSLog(@"the sum age is %@",[person valueForKeyPath:@"[email protected]"]);
    NSLog(@"the count person is %@",[person valueForKeyPath:@"[email protected]"]);
    NSLog(@"the min age is %@",[person valueForKeyPath:@"[email protected]"]);
    NSLog(@"the max age is %@",[person valueForKeyPath:@"[email protected]"]);
    
}
-(void)setage:(Person *)person age:(NSString *)age{
    [person setValue: age forKey:@"age"];
}

输出

2014-11-26 23:51:00.180 KVCtest[1346:42300] other's age is (
    20,
    21,
    22,
    23
)
2014-11-26 23:51:00.183 KVCtest[1346:42300] the avg age is 21.5
2014-11-26 23:51:00.183 KVCtest[1346:42300] the sum age is 86
2014-11-26 23:51:00.184 KVCtest[1346:42300] the count person is 4
2014-11-26 23:51:00.184 KVCtest[1346:42300] the min age is 20
2014-11-26 23:51:00.184 KVCtest[1346:42300] the max age is 23

本文参考 容芳志博客，感谢这位博友

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