Add Custom Image in Navigation Bar for Both iOS4 and iOS5

As you know, until iOS 5 came out, we used drawRect override in AppDelegate to customize UINavigationBar.
Now iOS 5 give us some new method for styling (and old doesn’t work).
How to build app that will work on iOS 4 and iOS 5 with stylized UINavigationBar?
You must to do both!
In AppDelegate use this code:

@implementation UINavigationBar (UINavigationBarCategory)
- (void)drawRect:(CGRect)rect {
UIImage *img = [UIImage imageNamed:@"navbar.png"];
[img drawInRect:rect];
}
@end

and in viewDidLoad method for iOS5 (in your view implementation):

if ([self.navigationController.navigationBar respondsToSelector:@selector( setBackgroundImage:forBarMetrics:)]){
[self.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:@"navbar.png"] forBarMetrics:UIBarMetricsDefault];
}

If you see, here we are asking if navbar will respondToSelector to avoid crash on iOS4!
If you use this for iOS5:

if([[UINavigationBar appearance] respondsToSelector:@selector( setBackgroundImage:forBarMetrics:)]){
[[UINavigationBar appearance] setBackgroundImage:[UIImage imageNamed:@"navbar_bg.png"] forBarMetrics:UIBarMetricsDefault];
}


Your app will not work on iOS4 because can’t found [UINavigationBar appearance].
But, if you want to target only iOS5 this snippet will work for whole app. You can put it just in didFinishLaunchingWithOptions method in AppDelegate:

[[UINavigationBar appearance] setBackgroundImage:[UIImage imageNamed:@"navbar_bg.png"] forBarMetrics:UIBarMetricsDefault];
}