KVO即“键值监听”，通常需要三步：
1、添加监听对象【addObserver: forKeyPath: options: context:】
2、执行监听代理【- (void)observeValueForKeyPath:(NSString*)keyPath ofObject:(id)object{}】
3、移除监听【removeObserver: forKeyPath: context: 】
图片示例：
代码示例：
//----------在.h文件中
#import<UIKit/UIKit.h>
@interfaceViewController :UIViewController
@end
//----------在.m文件中
#import"ViewController.h"
@interface ViewController()
@property(nonatomic ,strong)NSString *price;
@end
@implementation ViewController
- (void)viewDidLoad {
[superview DidLoad];
self.price=@"10";
//添加监听对象
[self addObserver:self forKeyPath:@"price" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];
NSLog(@"---------%@",_price);
[self performSelector:@selector(changeGrade) withObject:nil afterDelay:5.0];
}
- (void)changeGrade {
self.price=@"10000";
}
//执行监听代理
- (void)observeValueForKeyPath:(NSString*)keyPath ofObject:(id)object
change:(NSDictionary*)change context:(void*)context
{
if(object ==self && [keyPath isEqualToString:@"price"]) {
NSLog(@"---------%@",_price);
}else{
[super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
}
}
//移除监听
- (void)dealloc {
[self removeObserver:self forKeyPath:@"price" context:nil];
}
@end
