KVO 键值观察,简单来说就是为一个key添加一个观察者，当key的值发生改变的时候会发送通知，在接到通知的时候会有回调方法被调用
#import "ViewController.h"
@interface ViewController (){
NSMutableDictionary * myDict;
}
@end
@implementation ViewController
- (IBAction)dasdas:(id)sender {
//改变key的值
NSString * key = [myDict objectForKey:@"key"];
if ([key isEqualToString:@"key1"]) {
[myDict setValue:@"key2" forKey:@"key"];
}else {
[myDict setValue:@"key1" forKey:@"key"];;
}
key = [myDict objectForKey:@"key"];
NSLog(@"%@",key);
}
- (void)dealloc {
//移除观察者
[myDict removeObserver:self forKeyPath:@"key"];
}
- (void)viewDidLoad {
[super viewDidLoad];
myDict = [[NSMutableDictionary alloc] init];
[myDict setValue:@"key1" forKey:@"key"];
//添加观察者
[myDict addObserver:self forKeyPath:@"key" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:nil];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
//观察者观察的对象发生改变的时候调用的方法
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
if ([keyPath isEqualToString:@"key"]) {
NSString * key = [(NSDictionary *)object objectForKey:@"key"];
if ([key isEqualToString:@"key1"]) {
self.view.backgroundColor = [UIColor greenColor];
}else {
self.view.backgroundColor = [UIColor orangeColor];
}
}
}
@end
原文：http://my.oschina.net/u/2253117/blog/489029