GCD 注册通知

    id observer1,observer2,observer3,observer4;
    observer1 = [[NSNotificationCenter defaultCenter] addObserverForName:SIAlertViewWillShowNotification
                                                                  object:alertView
                                                                   queue:[NSOperationQueue mainQueue]
                                                              usingBlock:^(NSNotification *note) {
                                                                  NSLog(@"%@, -willShowHandler3", alertView);
                                                              }];