实例化长按手势监听
//实例化长按手势监听
UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(btnLong:)];
//代理
longPress.delegate = self;
longPress.minimumPressDuration = 0.5;
[self.label_num addGestureRecognizer:longPress];