iOS监听控件某个属性的改变observeValueForKeyPath

#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;    });}

/** *  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"]);    }}

2015-06-30 11:48:32.001 监听控件某个属性的改变[34212:570638] self.button的enabled属性改变了1