如何在iOS 7中的导航栏上获得模糊和半透明效果？

Question

Problem

My app appears to be laid out correctly, but I cannot achieve the blurry translucent effect that iOS 7 is famous for. Mine appears opaque.

Desired Effect

I'm trying to get a more obvious blur effect such as Apple's Trailers app:

Translucency

In my subclass of UINavigationController, I make the navigation bar translucent:

- (id)initWithRootViewController:(UIViewController *)rootViewController
{
    if (self = [super initWithRootViewController:rootViewController]) {
        self.navigationBar.translucent = YES;
    }
    return self;
}

Tint Color

In my subclass of UIApplicationDelegate, I set the tint color of the navigation bar. I discovered that the alpha of the tint color makes no difference. That is, using an alpha of 0.1 would not cause the bar to become more translucent.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{
    [[UINavigationBar appearance] setTintColor:[UIColor greenColor]];
}

Edges

In my content view controller, I set the edge to UIRectEdgeNone so the top doesn't get chopped off by the navigation bar. If I were to use the default UIRectEdgeAll , the navigation bar would permanently cover the top of my content. Even if I were to live with this abnormality, UIRectEdgeAll still does not enable the translucency effect.

- (void) viewDidLoad
{
    [super viewDidLoad];
    self.edgesForExtendedLayout = UIRectEdgeNone;
}

Edit: Experimenting with Edges

Ad pointed out by @rmaddy in the comments, the problem may be with the edgesForExtendedLayout. I found a comprehensive tutorial edgesForExtendedLayout and attempted to implement it:

- (void) viewDidLoad
{
    [super viewDidLoad];

    self.edgesForExtendedLayout = UIRectEdgeAll;
    self.automaticallyAdjustsScrollViewInsets = YES;
    self.extendedLayoutIncludesOpaqueBars = NO;
}

It did not work. Firstly, there was no translucency effect. Secondly, the top of my content was chopped off. On the following example page with the above code, the avatar was initially covered by the navigation bar and it was very hard to scroll to. You could pull down to see the top of the avatar, but when you let go, the page would automatically bounce back up and the avatar would be obscured again.

Answer 1

The problem was caused by the third party pull-down-to-refresh view EGORefreshTableHeaderView , which was popularly used before iOS 6 introduced the system refresh control.

This view confuses iOS 7, making it think that the content is taller than it really is. For iOS 6 and 7, I've conditionally switched to using UIRefreshControl . Now the navigation bar will not chop off my content. I can use UIRectEdgeAll to make my content go underneath the navigation bar. Finally, I tint my navigation bar with a lower alpha to get the translucency effect.

// mostly redundant calls, because they're all default
self.edgesForExtendedLayout = UIRectEdgeAll;
self.automaticallyAdjustsScrollViewInsets = YES;
self.extendedLayoutIncludesOpaqueBars = NO;

[[UINavigationBar appearance] setTintColor:[UIColor colorWithWhite:0.0 alpha:0.5]];

Answer 2

If you need to achieve exactly the same effect as in the iTunes Store (Dark Blur).

Configure the barStyle attribute of the navigation bar as follows:

self.navigationController.navigationBar.barStyle = UIBarStyleBlack;