KVC 監聽某對象屬性值的改變

//被監控的類

@interface Person : NSObject{

NSString *name;

}

@property(retain) NSString *name; //被監控的屬性

@end

@implementation Person

@synthesize name;

@end

//觀察者

@interface KVCObserver : NSObject

{}

@end

@implementation KVCObserver

//callback

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

NSLog(@"value change! key path :%@",keyPath);

NSLog(@"object : %@",object);

NSLog(@"old value: %@",[change objectForKey: NSKeyValueChangeOldKey ]);

NSLog(@"new value: %@",[change objectForKey: NSKeyValueChangeNewKey ]);

}

@end

KVCObserver *vc = [[VCObserver alloc] init];

Person *friend = [[Person alloc] init];

friend.name = @"jack";

[friend addObserver:vc forKeyPath:@"name" options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld) context:nil];

[friend setName:@"jory"]; //執行後将call 到vc