KVO

通过kvc的方式修改被观察者的属性时 主动通知观察者

注册observing对象addObserver:forKeyPath:options:context:委托代理

观察者类必须重写方法 observeValueForKeyPath:ofObject:change:context:

kvo是同步的

应用场景:

MVC模型中，数据库（dataModal）发生变化时，引起view改变，用这种方式实现非常方便

代码:

新建model person

 

@interface Person : NSObject
@property (nonatomic, assign) int age;
+(instancetype)personWithDict:(NSDictionary *)dict;
@end
+(instancetype)personWithDict:(NSDictionary *)dict
{
id obj = [[self alloc]init];
[obj setValuesForKeysWithDictionary:dict];
return obj;
}

　　

 
- (void)viewDidLoad {
[super viewDidLoad];
self.person = [Person personWithDict:@{@"age":@(100)}];
/*
1.谁进行观察
2.观察哪个属性
3.观察者的选项
4.场景 可以根据监听时来判断
*/
[self.person addObserver:self forKeyPath:@"age" options:NSKeyValueObservingOptionNew context:nil];
}

　　

 
//添加监听后 一旦监听到更改会调用此方法
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
{
NSLog(@"keypath:%@ obj:%@ change:%@ context:%@",keyPath,object,change,context);
}
-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
self.person.age = self.person.age -1;
NSLog(@"%d",self.person.age);
}