iOS KVO

KVO 即Key_Value Observing,它是一种观察者设计模式,当被观察者对象的属性被修改后,KVO就会自动通知响应的观察者,观察者就会调用响应的方法

步骤:

1.注册,指定被观察者的属性

2.实现回调方法

3.移除观察者

创建一个Person类

@interface Person : NSObject

{
    NSString * name;
    NSString *pid;
    
}
@end

在ViewController.m文件

#import "ViewController.h"
#import "Person.h"
@interface ViewController ()
@property(nonatomic,retain)Person *dm;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
 
    self.dm=[[Person alloc]init];
    
    [_dm setValue:@"daren" forKey:@"name"];
    [_dm setValue:@"1" forKey:@"pid"];
    
    //注册观察者
    [_dm addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];
    UILabel *testLabel =[[UILabel alloc]init];
    testLabel.frame=CGRectMake(20, 20, 100, 30);
    testLabel.backgroundColor=[UIColor clearColor];
    testLabel.tintColor=[UIColor blackColor];
    testLabel.tag=1001;
    
    testLabel.text=[_dm valueForKey:@"name"];
    [self.view addSubview:testLabel];
    
    UIButton * button=[UIButton buttonWithType:UIButtonTypeRoundedRect];
    button.frame=CGRectMake(20, 100, 100, 70);
    [button setTitle:@"测试" forState:UIControlStateNormal];
    
    [button addTarget:self action:@selector(testPressed) forControlEvents:UIControlEventTouchUpInside];
    
    [self.view addSubview:button];
    
}

//按钮响应事件
- (void)testPressed{
    
    [_dm setValue:@"wangzi" forKey:@"name"];
    
    
}


//当被观察者的属性改变时,系统就会通知观察者,并且会这行下列这个方法
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
   
    UILabel * label=(UILabel *)[self.view.superview viewWithTag:1001];
    
    if ([keyPath isEqualToString:@"name"]) {
        
        label.text=[_dm valueForKey:@"name"];
        
        
    }
    
    

}

-(void)dealloc{
    [super dealloc];
    
    //移除观察者
    [_dm removeObserver:self forKeyPath:@"name"];
    
    [_dm release];
    
    
    
}