- (void)setTabBarVisible:(BOOL)visible animated:(BOOL)animated {

    // bail if the current state matches the desired state

    if ([self tabBarIsVisible] == visible) return;

    // get a frame calculation ready

    CGRect frame = self.tabBarController.tabBar.frame;

    CGFloat height = frame.size.height;

    CGFloat offsetY = (visible)? -height : height;

    // zero duration means no animation

    CGFloat duration = (animated)? 0.3 : 0.0;

    [UIView animateWithDuration:duration animations:^{

        self.tabBarController.tabBar.frame = CGRectOffset(frame, 0, offsetY);

    }];

}

// know the current state

- (BOOL)tabBarIsVisible {

    return self.tabBarController.tabBar.frame.origin.y < CGRectGetMaxY(self.view.frame);

}

- (void)buttonClick{

    [self setTabBarVisible:![self tabBarIsVisible] animated:YES];

}