KVC + KVO

KVC

//KVC赋值对象的属性

[p1 setValue:@"" forKey:@"name"];

KVO

• (void)viewDidLoad {
  [super viewDidLoad];

  //1.初始化对象
  _p1 = [[Person alloc] init];

  //2.添加观察者对象
  //参数1：监听的对象
  //参数2：当前对象
  //参数3：新值和旧值
  //参数4：形参内容
  [_p1 addObserver:self forKeyPath:@”name” options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew context:@”hello”];
  }

• (void)changeValue
  {
  //3.通过kvc改修对象属性的值
  NSString *name = [NSString stringWithFormat:@”%d”,arc4random() % 100000];
  [_p1 setValue:name forKey:@”name”];
  }

//4.对象属性值修改时回调
- (void)observeValueForKeyPath:(NSString )keyPath ofObject:(id)object change:(NSDictionary )change context:(void *)context
{
//keyPath属性名字
if ([keyPath isEqualToString:@”name”]) {
//object被监听的对象 person的对象
Person p1 = (Person )object;
_label.text = p1.name;
}

//change新值 和 旧值//context 形参值

// NSLog(@”keyPath == %@”,keyPath);
// NSLog(@”object == %@”,object);
// NSLog(@”change == %@”,change);
// NSLog(@”context == %@”,context);
}

KVO反向传值

//VC1

• (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
  _label = [[UILabel alloc] initWithFrame:CGRectMake(100, 200, 200, 50)];
  _label.backgroundColor = [UIColor grayColor];
  _label.textColor = [UIColor redColor];
  [self.view addSubview:_label];

  //1.初始化被监听的对象
  self.second = [[SecondViewController alloc] init];

  //2.添加观察者对象
  [self.second addObserver:self forKeyPath:@”name” options:NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew context:nil];
  }

• (void)touchesBegan:(NSSet )touches withEvent:(UIEvent )event
  {
  [self presentViewController:self.second animated:YES completion:nil];
  }

//4.对象的属性被修改时的回调
- (void)observeValueForKeyPath:(NSString )keyPath ofObject:(SecondViewController )object change:(NSDictionary )change context:(void )context
{
if ([keyPath isEqualToString:@”name”]) {
_label.text = object.name;
}
}

//VC2

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event

{
//3.修改对象属性的值
[self setValue:@”KVO反向传值” forKey:@”name”];
[self dismissViewControllerAnimated:YES completion:nil];
}