How to fade BOTH status bar and navigation bar LIKE Photos.app, on iOS 7 - ios7

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?