IOS开发之KVC与KVO简述

KVC:Key-Value Coding

KVO:Key-Value Observing

 

Person.m

#import <Foundation/Foundation.h>



@interface Person : NSObject{

    //该访问修饰符用于说明即使私有成员变量也可以通过kvc方式访问和赋值

    @private

    NSString *_name;

    NSArray *_dogs;

}

@end



@implementation Person

@end

Dog.m

#import <Foundation/Foundation.h>



@class Person;



@interface Dog : NSObject

{

    @private

    NSInteger _age;

    Person *_owner;

}

@end



@implementation Dog

@end

PersonObserve.m

#import <Foundation/Foundation.h>

#import "Person.h"



@interface PersonObserve : NSObject

@end



@implementation PersonObserve

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{

    Person *p = (Person *)object;

    //使用kvc方式获取成员变量keypath的值

    NSLog(@"%@",[p valueForKey:keyPath]);

}

@end

main.m

#import <Foundation/Foundation.h>

#import "Person.h"

#import "PersonObserve.h"

#import "Dog.h"



int main(int argc, const char * argv[]) {

    //观察者类

    PersonObserve *po = [[PersonObserve alloc] init];

    Person *p = [[Person alloc] init];

    //使用kvo方式对成员变量“name”的属性值变化增加观察者po

    //po将在该属性值发生变化时执行- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context方法

    [p addObserver:po forKeyPath:@"name" options:NSKeyValueObservingOptionNew context:nil];

    

    //通过kvc方式设置成员变量“name”的属性值

    //出发观察者执行对应方法

    [p setValue:@"zhangsan" forKey:@"name"];

    

    

    //kvc中forKeyPath的用法

    Dog *d = [[Dog alloc] init];

    [d setValue:p forKey:@"owner"];

    [d setValue:@"lisi" forKeyPath:@"owner.name"];

    

    //移除对私有成员变量“name”的观察

    [p removeObserver:po forKeyPath:@"name"];

    

    

    Dog *d1 = [[Dog alloc] init];

    [d1 setValue:@10 forKey:@"age"];

    Dog *d2 = [[Dog alloc] init];

    [d2 setValue:@20 forKey:@"age"];

    

    

    NSArray *array = [NSArray arrayWithObjects:d1,d2, nil];

    [p setValue:array forKey:@"dogs"];

    

    

    //kvc中valueForKeyPath数组内置表达式的用法

    NSLog(@"dogs.age = %@",[p valueForKeyPath:@"dogs.age"]);

    NSLog(@"dogs.age.sum = %@",[p valueForKeyPath:@"[email protected]"]);//dogs数组中age的总和

    NSLog(@"dogs.age.avg = %@",[p valueForKeyPath:@"[email protected]"]);//dogs数组中age的平均值

    NSLog(@"dogs.age.max = %@",[p valueForKeyPath:@"[email protected]"]);//dogs数组中age的最大值

    NSLog(@"dogs.age.min = %@",[p valueForKeyPath:@"[email protected]"]);//dogs数组中age的最小值

    

    

    return 0;

}

结果：

2015-03-07 21:09:34.611 KVC&KOC[3079:122638] zhangsan

2015-03-07 21:09:34.612 KVC&KOC[3079:122638] lisi

2015-03-07 21:09:34.613 KVC&KOC[3079:122638] dogs.age = (

    10,

    20

)

2015-03-07 21:09:34.613 KVC&KOC[3079:122638] dogs.age.sum = 30

2015-03-07 21:09:34.613 KVC&KOC[3079:122638] dogs.age.avg = 15

2015-03-07 21:09:34.613 KVC&KOC[3079:122638] dogs.age.max = 20

2015-03-07 21:09:34.613 KVC&KOC[3079:122638] dogs.age.min = 10

Program ended with exit code: 0