iOS 简单的描述KVO使用

//

//  ViewController.m

//  KVOtest

//

//  Created by Mac on 15/10/17.

//  Copyright © 2015年 聂小波. All rights reserved.

//

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic, strong) UIButton *kvobtn;

@end

@implementation ViewController

- (void)viewDidLoad {

[super viewDidLoad];

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

_kvobtn=[UIButton new];

_kvobtn.tag=10;

//对属性添加值改变监听

[_kvobtn addObserver:self forKeyPath:@"tag" options:NSKeyValueObservingOptionNew context:nil];

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(4.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

//改变属性值

_kvobtn.tag=11;

});

}

#pragma mark- KVO获得值改变调用

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

if ([keyPath isEqualToString:@"tag"]) {

NSLog(@"===============changed===============");

}

}

#pragma mark- 移除监听，如果没有移除会导致崩溃

-(void)dealloc{

[self removeObserverFromUIButton:_kvobtn];

[self removeNotification];

}

-(void)removeObserverFromUIButton:(UIButton *)kvobtn{

[kvobtn removeObserver:self forKeyPath:@"tag"];

}

-(void)removeNotification{

[[NSNotificationCenter defaultCenter] removeObserver:self];

}

@end