KVO

添加

addObserver:forKeyPath: options:context:

- (void)addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(nullable void *)context;

• observer - 监听器
• keyPath - key
• options

typedef NS_OPTIONS(NSUInteger, NSKeyValueObservingOptions) {
    NSKeyValueObservingOptionNew = 0x01,
    NSKeyValueObservingOptionOld = 0x02,
    NSKeyValueObservingOptionInitial = 0x04,
    NSKeyValueObservingOptionPrior = 0x08
};

• context - Arbitrary data that is passed to observer in [observeValueForKeyPath:ofObject:change:context:]

移除

- (void)removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath 
context:(nullable void *)context
- (void)removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath

监听方法

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

应用

@interface NSPerson : NSObject

@property(nonatomic,assign)int  age;
@property(nonatomic,assign)double  height;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.person = [NSPerson new];
    self.person.age = 10;
    self.person.height = 180;
    
    NSKeyValueObservingOptions options = NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld;
    
    [self.person addObserver:self forKeyPath:@"age" options:options context:nil];
    [self.person addObserver:self forKeyPath:@"height" options:options context:nil];

}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{    
    NSLog(@"keyPath:%@",keyPath);
    NSLog(@"object:%s",object_getClassName(object));
    NSLog(@"change:%@",change);
    NSLog(@"context:%@",context);
}

- (void)dealloc
{
    [self.person removeObserver:self forKeyPath:@"age"];
    [self.person removeObserver:self forKeyPath:@"height"];
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    self.person.age = 20;
    self.person.height = 182;
    
}


@end

log

2020-06-27 22:56:25.704268+0800 KVO[61945:2417667] keyPath:age
2020-06-27 22:56:25.704641+0800 KVO[61945:2417667] object:NSKVONotifying_NSPerson
2020-06-27 22:56:25.705091+0800 KVO[61945:2417667] change:{
    kind = 1;
    new = 20;
    old = 10;
}
2020-06-27 22:56:25.705399+0800 KVO[61945:2417667] context:(null)
2020-06-27 22:56:25.705589+0800 KVO[61945:2417667] keyPath:height
2020-06-27 22:56:25.705745+0800 KVO[61945:2417667] object:NSKVONotifying_NSPerson
2020-06-27 22:56:25.705950+0800 KVO[61945:2417667] change:{
    kind = 1;
    new = 182;
    old = 180;
}
2020-06-27 22:56:25.706678+0800 KVO[61945:2417667] context:(null)