KVO初探

//
//  ViewController.m
//  KvoTest
//
//  Created by luzheng1208 on 14/12/7.
//  Copyright (c) 2014年 luzheng. All rights reserved.
//

#import "ViewController.h"

@interface ViewController () {
    
}

@property (strong, nonatomic) NSString *name;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.name = @"Xiao Ming";
    [self registerForKVO];
    
    //[self willChangeValueForKey:@"name"];
    self.name = @"Xiao Hong";
    self.name = @"Xiao Li";
    //[self didChangeValueForKey:@"name"];
}

- (void)dealloc {
    [self unregisterForKVO];
}

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



#pragma mark - KVO

- (void)registerForKVO {
    [self addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:NULL];
}

- (void)unregisterForKVO {
    [self removeObserver:self forKeyPath:@"name"];
}


- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if ([keyPath isEqualToString:@"name"]) {
        NSLog(@"The old value is %@", [change objectForKey:NSKeyValueChangeOldKey]);
        NSLog(@"The new value is %@", [change objectForKey:NSKeyValueChangeNewKey]);
    }
    else
    {
        [super observeValueForKeyPath:keyPath
                             ofObject:object
                               change:change
                              context:context];
    }
}


@end

2014-12-07 23:02:38.951 KvoTest[19553:2584967] The old value is Xiao Ming
2014-12-07 23:02:38.954 KvoTest[19553:2584967] The new value is Xiao Hong
2014-12-07 23:02:38.954 KvoTest[19553:2584967] The old value is Xiao Hong
2014-12-07 23:02:38.954 KvoTest[19553:2584967] The new value is Xiao Li