ios 监听一个控制器的属性_ios - kvo观察者示例(监听类的属性变化)

首先创建Person分类

#import

@interface Person : NSObject

@property (nonatomic, copy) NSString *name;

@property (nonatomic, assign) float height;

@end

.m中不做任何事情

控制器.m中

#import "ViewController.h"

#import "Person.h"

@interface ViewController ()

@property (nonatomic, strong) Person *per;

@end

@implementation ViewController

- (void)viewDidLoad {

[super viewDidLoad];

Person * per = [Person new];

per.name = @"zhangsan";

per.height = 1.2;

self.per = per;

// kvo 为per.name添加观察者

[per addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];

// kvo 为per.height添加观察者

[per addObserver:self forKeyPath:@"height" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];

}

只要监听的属性name 和 height的值发生了改变就会触发下面的方法

/** 添加观察者必须要实现的方法 */

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

/** 打印新老值 */

// 从打印结果看分别打印出了 name 与 height的新老值

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

// NSLog(@"keypath : %@",keyPath);

// NSLog(@"change : %@",change);

}

由于对person.name 以及height的属性都做了监听,只要触摸后属性的值发生改变就做得到通知触发通知方法 -(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context 则可以在其内部做你想要做的事

/** 触摸改变per.name属性值 */

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{

self.per.name = @"helloworld";

self.per.height = 3.3;

}

一定要记得移除

/** 移除 */

-(void)dealloc{

[self.per removeObserver:self forKeyPath:@"name" context:nil];

[self.per removeObserver:self forKeyPath:@"height" context:nil];

}

- (void)didReceiveMemoryWarning {