#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:@"測試" forState:UIControlStateNormal];    [self.button setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];    self.button.layer.borderWidth = 1.0f;    [self.view addSubview:self.button];        //注冊監聽button的enabled狀態    [self.button addObserver:self forKeyPath:@"enabled" options:NSKeyValueObservingOptionNew context:@"test_button"];        //  3秒鐘后改變當前button的enabled狀態    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3.0f * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{        self.button.enabled = YES;    });}

/** *  監聽按鈕狀態改變的方法 * *  @param keyPath 按鈕改變的屬性 *  @param object  按鈕 *  @param change  改變后的數據 *  @param context 注冊監聽時context傳遞過來的值 */-(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屬性改變了%@",[change objectForKey:@"new"]);    }}

2015-06-30 11:48:32.001 監聽控件某個屬性的改變[34212:570638] self.button的enabled屬性改變了1