1 //
 2 //  Walker.h
 3 //  KVOExample
 4 //
 5 //  Created by 老翁 on 13-7-29.
 6 //  Copyright (c) 2013年 wzl. All rights reserved.
 7 //
 8
 9 #import <Foundation/Foundation.h>
10
11 @interface Walker : NSObject
12 {
13     NSInteger _age;
14     NSString *_name;
15 }
16
17 @property (nonatomic) NSInteger age;
18 @property (nonatomic, retain) NSString *name;
19
20 - (id)initWithName:(NSString *)name age:(NSInteger)age;
21
22
23 @end

#import "Walker.h"@implementation Walker@synthesize age = _age;
@synthesize name = _name;- (void)dealloc
{[_name release];[super dealloc];
}- (id)initWithName:(NSString *)name age:(NSInteger)age
{if (self = [super init]) {_name = name;_age = age;}return  self;
}@end

//
//  ViewController.h
//  KVOExample
//
//  Created by 老翁 on 13-7-29.
//  Copyright (c) 2013年 wzl. All rights reserved.
//

#import <UIKit/UIKit.h>
#import "Walker.h"@class Walker;@interface ViewController : UIViewController
{Walker *_walker;UILabel *_ageLabel;
}@property (nonatomic, assign) Walker *walker;@end

 1 //
 2 //  ViewController.m
 3 //  KVOExample
 4 //
 5 //  Created by 老翁 on 13-7-29.
 6 //  Copyright (c) 2013年 wzl. All rights reserved.
 7 //
 8
 9 #import "ViewController.h"
10
11 @interface ViewController ()
12
13 @end
14
15 @implementation ViewController
16
17 @synthesize walker = _walker;
18
19
20 - (void)dealloc
21 {
22     [_walker release];
23     [_ageLabel release];
24     [super dealloc];
25 }
26
27 - (void)viewDidLoad
28 {
29     [super viewDidLoad];
30     // Do any additional setup after loading the view, typically from a nib.
31     _walker = [[Walker alloc] initWithName:@"老翁" age:25];
32     /* 关键步骤 */
33     [_walker addObserver:self
34               forKeyPath:@"age"
35                  options:NSKeyValueObservingOptionNew
36                  context:nil];
37
38
39     //UI initialization
40     UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];
41     [btn setFrame:CGRectMake(120, 200, 100, 35)];
42     [btn setBackgroundColor:[UIColor lightGrayColor]];
43     [btn setTitle:@"增加5岁" forState:UIControlStateNormal];
44     [btn addTarget:self
45             action:@selector(buttonPressed)
46   forControlEvents:UIControlEventTouchUpInside];
47     [self.view addSubview:btn];
48
49     _ageLabel = [[UILabel alloc] initWithFrame:CGRectMake(40, 150, 200, 35)];
50     _ageLabel.text = [NSString stringWithFormat:@"%@现在的年龄是: %d", _walker.name, _walker.age];
51     _ageLabel.backgroundColor = [UIColor clearColor];
52     [self.view addSubview:_ageLabel];
53
54
55 }
56
57 - (void)buttonPressed
58 {
59     _walker.age += 5;
60 }
61
62 /* KVO function， 只要object的keyPath属性发生变化，就会调用此函数*/
63 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
64 {
65     if ([keyPath isEqualToString:@"age"] && object == _walker) {
66         _ageLabel.text = [NSString stringWithFormat:@"%@现在的年龄是: %d", _walker.name, _walker.age];
67     }
68 }
69
70
71
72 - (void)didReceiveMemoryWarning
73 {
74     [super didReceiveMemoryWarning];
75     // Dispose of any resources that can be recreated.
76 }
77
78 @end