KVO的简单用法

#import "ViewController.h"
#import "Person.h"
@interface ViewController ()
{
    Person *_p;
}
@end

@implementation ViewController
-(void)dealloc
{
    [_p removeObserver:self forKeyPath:@"name"];
    [_p release];
    [super dealloc];
}
- (void)viewDidLoad
{
    [super viewDidLoad];
   
    //p用作被观察者
    _p = [[Person alloc] init];
    
    [_p addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:@"hello"];
    _p.name = @"lisi";

    // Do any additional setup after loading the view, typically from a nib.
}

//被观察者的属性发生变化时,才会触发此方法
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSLog(@"object = %@",object);
    NSLog(@"keyPath = %@",keyPath);
    NSLog(@"change  = %@",change);
    NSLog(@"context = %@",context);
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end