How to fade BOTH status bar and navigation bar LIKE Photos.app, on iOS 7

Question

Basically, it's a very simple demand, but I've tried several methods and none of them works as expected. The closest functioning snippet is:

#import "ViewController.h"

@implementation ViewController

- (void)dealloc
{
    [scrollView release];
    scrollView = nil;

    [super dealloc];
}

- (id)init
{
    if (self = [super init])
    {
        self.title = @"Pictures";

        scrollView = [[UIScrollView alloc] init];
        scrollView.delegate = self;
        scrollView.frame = CGRectMake(0.0f, 0.0f, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height);
        scrollView.contentSize = CGSizeMake([UIScreen mainScreen].bounds.size.width * 10, scrollView.bounds.size.height);
        scrollView.showsVerticalScrollIndicator = NO;
        scrollView.showsHorizontalScrollIndicator = NO;
        scrollView.pagingEnabled = YES;
        scrollView.userInteractionEnabled = YES;
        scrollView.backgroundColor = [UIColor blackColor];
        self.wantsFullScreenLayout = YES;
        self.automaticallyAdjustsScrollViewInsets = NO;
        isHidden = NO;
    }
    return self;
}

- (void)viewDidLoad
{
    UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tap:)];
    [scrollView addGestureRecognizer:tapGesture];
    [tapGesture setNumberOfTapsRequired:1];
    [tapGesture release];

    for (int i = 0; i < 10; i++)
    {
        UIImage *image = [[UIImage alloc] initWithContentsOfFile:[NSString stringWithFormat:@"/path/to/%d.png", i + 1]];
        UIImageView *imageView= [[UIImageView alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width * i, 0.0f, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height)];
        imageView.contentMode = UIViewContentModeScaleAspectFit;
        imageView.image = image;
        [scrollView addSubview:imageView];
        [image release];
        [imageView release];
    }

    [self.view addSubview:scrollView];
}

- (void)tap:(UITapGestureRecognizer *)gesture
{
    [UINavigationBar setAnimationDuration:1.0];
    [UINavigationBar beginAnimations:@"HideTopBars" context:nil];

    isHidden = !isHidden;
    // [self setNeedsStatusBarAppearanceUpdate];

    self.navigationController.navigationBar.alpha = isHidden ? 0.0f : 1.0f;
    [UINavigationBar commitAnimations];
}

- (void)scrollViewDidScroll:(UIScrollView *)view
{
    // further operation
}

- (BOOL)prefersStatusBarHidden
{
    return isHidden;
}
@end

Without "[self setNeedsStatusBarAppearanceUpdate]", navigation bar does fade as expected, but texts on status bar remain visible, which I guess is because status bar takes navigation bar as it's background image and status bar itself doesn't fade; With "[self setNeedsStatusBarAppearanceUpdate]", the texts also fade, but navigation bar's animation becomes sliding in/out from the top of the screen along with fade effect. I've also tried to move "[self setNeedsStatusBarAppearanceUpdate]" into prefersStatusBarHidden, but that just made navigation bar visible forever. I believe this is not an odd demand, so I bet there're better and simpler solutions. Any idea?