7.11 KVC和KVO

KVC

• 定义：键值编码

• 使用

     //1.直接存键值
     [p1 setValue:@"lisi"forKey:@"name"];
     //2.通过path存键值
     [p1 setValue:@"随便"forKeyPath:@"book.bookName"];
     //3.字典转模型
     NSDictionary *dict =@{@"name":@"wangwu",@"age":@"40"};
     [p1 setValuesForKeysWithDictionary:dict];
     //kvc 和数组
     Person *p2 = [[Personalloc] init];
      p2.name = @"yellow Mokey";
  
      Person *p3 = [[Personalloc] init];
      p3.name = @"red dog";
  
      Person *p4 = [[Personalloc] init];
      p4.name =@"green chicken";
  
      NSArray *array = @[p2,p3,p4];
  
      // 把三个对象中的name 取出来
  
      NSArray *nameArray = [array valueForKeyPath:@"name"];
  
      NSLog(@"%@",nameArray);
  

• 赋值过程

  
  5aad7573.jpg

• 取值过程

  
  13a6261e.jpg

面试题

• 通过KVC修改属性会触发KVO么？
  • 会触发KVO

KVO

• 定义：键值监听

  #import "MJPerson.h"
  
  @interface ViewController ()
  @property (strong, nonatomic) MJPerson *person1;
  @property (strong, nonatomic) MJPerson *person2;
  @end
  
  @implementation ViewController
  
  - (void)viewDidLoad {
    [super viewDidLoad];
  
    self.person1 = [[MJPerson alloc] init];
    self.person1.age = 1;
    self.person1.height = 11;
  
  
    // 给person1对象添加KVO监听
    NSKeyValueObservingOptions options = NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld;
    [self.person1 addObserver:self forKeyPath:@"age" options:options context:@"123"];
    [self.person1 addObserver:self forKeyPath:@"height" options:options context:@"456"];
  }
  
  - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
  {
    self.person1.age = 20;
   
    self.person1.height = 30;
    
  }
  
  - (void)dealloc {
    [self.person1 removeObserver:self forKeyPath:@"age"];
    [self.person1 removeObserver:self forKeyPath:@"height"];
  }
  
  // 当监听对象的属性值发生改变时，就会调用
  - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context
  {
    NSLog(@"监听到%@的%@属性值改变了 - %@ - %@", object, keyPath, change, context);
  }
  
  

面试题

• iOS用什么方式实现对一个对象的KVO？(KVO的本质是什么？)
  • 利用RuntimeAPI动态生成一个子类，并且让instance对象的isa指向这个全新的子类（NSKVONotifying_xxx）
  • 当修改instance对象的属性时，会调用Foundation的_NSSetXXXValueAndNotify函数
    • willChangeValueForKey:
    • 父类原来的setter
    • didChangeValueForKey:
    • 内部会触发监听器（Oberser）的监听方法( observeValueForKeyPath:ofObject:change:context:）
• 如何手动触发KVO？
  • 手动调用willChangeValueForKey:和didChangeValueForKey:

    [self.person1 willChangeValueForKey:@"age"];
    [self.person1 didChangeValueForKey:@"age"];
    

• 直接修改成员变量会触发KVO么？
  • 不会触发KVO