iOS KVC(Key-Value Coding)

常见用法：

• 获取值
  • valueForKey: 依据属性名取值
  • valueForKeyPath: 依据路径取值(如：[person valueForKeyPath:@”car.price”])
  • valueForUndefinedKey 默认实现是抛出异常。能够重写这个函数做错误处理 ( 比較少用 )
• 改动值
  
  • setValue:forKey: 依据属性设值
  • setValue:forKeyPath: 依据路径设值
  • setValue:forUndefinedKey:
  • setNilValueForKey: 当对非类对象属性设置nil时。调用。默认抛出异常
• 字典转模型
  
  • setValuesForKeysWithDictionary: 字典转模型

上代码：

定义一个HSCar类

//
//  HSCar.h
//  KVC
//
//  Created by hans on 15/7/13.
//  Copyright © 2015年 hans. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface HSCar : NSObject

/** 名字 */
@property (nonatomic, copy) NSString *name;

/** 价格 */
@property (nonatomic, assign) double price;

@end

定义一个HSBook类

//
//  HSBook.h
//  KVC
//
//  Created by hans on 15/7/13.
//  Copyright © 2015年 hans. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface HSBook : NSObject
/** 书名 */
@property (nonatomic, copy) NSString *name;
/** 价格 */
@property (nonatomic, assign) double price;
@end

定义一个HSPerson类

//
//  HSPerson.h
//  KVC
//
//  Created by hans on 15/7/13.
//  Copyright © 2015年 hans. All rights reserved.
//

#import <Foundation/Foundation.h>
@class HSCar;

@interface HSPerson : NSObject

/** 名字 */
@property (nonatomic, copy) NSString *name;

/** 年龄 */
@property (nonatomic, copy) NSString *age;

/** 车 */
@property (nonatomic, strong) HSCar *car;

@end

---

//
//  HSPerson.m
//  KVC
//
//  Created by hans on 15/7/13.
//  Copyright © 2015年 hans. All rights reserved.
//

#import "HSPerson.h"

@implementation HSPerson
{
    // 体重
    double _weight;
}

- (void)showWeight
{
    NSLog(@"weight: %f", _weight);
}

@end

在ViewController实现

//
//  ViewController.m
//  KVC
//
//  Created by hans on 15/7/13.
//  Copyright © 2015年 hans. All rights reserved.
//

#import "ViewController.h"
#import "HSPerson.h"
#import "HSCar.h"
#import "HSBook.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    HSPerson *person = [HSPerson new];
    person.name = @"hans";
    person.age = 23;

    person.car = [HSCar new];
    person.car.name = @"兰博基尼";
    person.car.price = 10000000.0;

    /** valueForKey: */
    NSLog(@"name: %@ age: %@", [person valueForKey:@"name"], [person valueForKey:@"age"]);
    // 2015-07-13 22:32:02.356 KVC[54356:872650] name: hans age: 23

    /** valueForKeyPath: */
    NSLog(@"name：%@ price： %@", [person valueForKeyPath:@"car.name"], [person valueForKeyPath:@"car.price"]);
    // 2015-07-13 22:51:27.075 KVC[54669:885579] name：兰博基尼 price： 10000000

    /** setValue:forKey: */
    [person setValue:@"hanshhh" forKey:@"name"];
    [person setValue:@"100" forKey:@"age"];
    NSLog(@"name: %@ age: %@", [person valueForKey:@"name"], [person valueForKey:@"age"]);
    // 2015-07-13 22:53:54.876 KVC[54709:886954] name: hanshhh age: 100

    /** setValue:forKeyPath: */
    [person setValue:@"法拉利" forKeyPath:@"car.name"];
    [person setValue:@(9999999) forKeyPath:@"car.price"];
    NSLog(@"name：%@ price： %@", [person valueForKeyPath:@"car.name"], [person valueForKeyPath:@"car.price"]);
    // 2015-07-13 22:56:36.336 KVC[54767:888926] name：法拉利 price： 9999999

    /** 更改私有属性 */
    [person setValue:@(120) forKeyPath:@"_weight"];
    [person showWeight];
    // 2015-07-13 23:01:15.151 KVC[54847:892122] weight: 120.000000

    /** 字典转模型 */
    // 1.简单转换
    NSDictionary *dict1 = @{
                           @"name"  : @"汉斯",
                           @"age" : @"23",
                           };

    [person setValuesForKeysWithDictionary:dict1];
    NSLog(@"name : %@, age : %d", person.name, person.age);
    // 2015-07-13 23:04:20.298 KVC[54943:895092] name : 汉斯, age : 23

    // 2.复杂模型转换(注意：person.car不能转换。会变为字典对象，事实上就是简单的指针赋值而已)
    NSDictionary *dict2 = @{
                           @"name"  : @"汉斯哈哈哈",
                           @"age" : @"23",
                           @"car" : @{
                                   @"name" : @"兰博基尼",
                                   @"price" : @"10000000"
                                   },
                            };
    [person setValuesForKeysWithDictionary:dict2];
    NSLog(@"%@", person.car);
//    2015-07-13 23:10:32.310 KVC[55019:899474] {
//        name = "\U5170\U535a\U57fa\U5c3c";
//        price = 10000000;
//    }

    /** 其它运算 */
    HSBook *book1 = [HSBook new];
    book1.name = @"结网";
    book1.price = 51.0;

    HSBook *book2 = [HSBook new];
    book2.name = @"失控";
    book2.price = 40.0;

    HSBook *book3 = [HSBook new];
    book3.name = @"异类";
    book3.price = 60.0;

    person.books = @[book1, book2, book3];

    NSLog(@"%@", [person.books valueForKeyPath:@"@count"]);
    NSLog(@"%@", [person.books valueForKeyPath:@"@avg.price"]);
    NSLog(@"%@", [person.books valueForKeyPath:@"@min.price"]);
    NSLog(@"%@", [person.books valueForKeyPath:@"@max.price"]);

//    2015-07-13 23:20:43.434 KVC[55171:905643] 3
//    2015-07-13 23:20:43.434 KVC[55171:905643] 50.333333333333333333333333333333333333
//    2015-07-13 23:20:43.435 KVC[55171:905643] 40
//    2015-07-13 23:20:43.435 KVC[55171:905643] 60
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end