FullScreen interaction for setting the top bars to be clear until content is scrolled up and the background has to be opaque.

FullScreen.m

#pragma mark - Hide and Show
#pragma mark -

- (void)prepareAnimationForNavigationBarWithDuration:(CGFloat)duration {
    // prepare animation for navigation bar
    CATransition *animation = [CATransition animation];
    [animation setDuration:duration];
    [animation setTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut]];
    [animation setType:kCATransitionFade];
    [self.navigationController.navigationBar.layer addAnimation:animation forKey:nil];
}

- (void)hideTopBars:(BOOL)animated withCompletionBlock:(void (^)())completionBlock {
    // sets a clear background for the top bars
    
    _topBarsClear = TRUE;
    
    CGFloat duration = animated ? 0.25f : 0.0f;
    
    [self prepareAnimationForNavigationBarWithDuration:duration];
    
    UIViewAnimationOptions options = UIViewAnimationOptionBeginFromCurrentState;
    [UIView animateWithDuration:duration delay:0.0 options:options animations:^{
        [self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
        self.navigationController.navigationBar.shadowImage = [UIImage new];
    } completion:^(BOOL finished) {
        if (finished && completionBlock) {
            completionBlock();
        }
    }];
}

- (void)showTopBars:(BOOL)animated withCompletionBlock:(void (^)())completionBlock {
    // sets the top bars to show an opaque background
    
    _topBarsClear = FALSE;
    
    CGFloat duration = animated ? 0.25f : 0.0f;
    
    [self prepareAnimationForNavigationBarWithDuration:duration];
    
    UIViewAnimationOptions options = UIViewAnimationOptionBeginFromCurrentState;
    [UIView animateWithDuration:duration delay:0.0 options:options animations:^{
        UIImage *backgroundImage = [SSTStyleKit imageOfBlueTopBarBackgroundImage];
        [self.navigationController.navigationBar setBackgroundImage:backgroundImage forBarMetrics:UIBarMetricsDefault];
    } completion:^(BOOL finished) {
        if (finished && completionBlock) {
            completionBlock();
        }
    }];
}

#pragma mark - UIScrollViewDelegate
#pragma mark -

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    //NSLog(@"offset: %f", scrollView.contentOffset.y);
    
    if (_topBarsClear) {
        if (scrollView.contentOffset.y > kCutOffPoint) {
            [self showTopBars:TRUE withCompletionBlock:nil];
        }
    }
    else {
        if (scrollView.contentOffset.y <= kCutOffPoint) {
            [self hideTopBars:TRUE withCompletionBlock:nil];
        }
    }
}