KVO(1)

#import "ViewController.h"

@interface ViewController ()
@property(nonatomic, strong)UIButton *button;

@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];
self.button = [[UIButton alloc] initWithFrame:CGRectMake(30, 50, 50, 30)];
[self.button setTitle:@"测试" forState:UIControlStateNormal];
[self.button setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
self.button.layer.borderWidth = 1.0f;
[self.view addSubview:self.button];

//注册监听button的enabled状态
[self.button addObserver:self forKeyPath:@"enabled" options:NSKeyValueObservingOptionNew context:@"test_button"];

//  3秒钟后改变当前button的enabled状态
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3.0f * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
self.button.enabled = YES;
});
// Do any additional setup after loading the view, typically from a nib.
}

/**
*  监听按钮状态改变的方法
*
*  @param keyPath 按钮改变的属性
*  @param object  按钮
*  @param change  改变后的数据
*  @param context 注册监听时context传递过来的值
*/
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
UIButton *button = (UIButton *)object;
if (self.button == button && [@"enabled" isEqualToString:keyPath]) {
NSLog(@"self.button的enabled属性改变了%@",[change objectForKey:@"new"]);
}
}