（此文为复制帖，原文地址为：http://blog.sina.com.cn/s/blog_a8192bdd0101af40.html）
self.navigationController.navigationBar.translucent = NO;
如果在iPad上用了split view，并且设置了UINavigationBar的background image，现象为状态栏一直是一片漆黑
UINavigationController will alter the height of its UINavigationBar to either 44 points or 64 points, depending on a rather strange and undocumented set of constraints. If the UINavigationController detects that the top of its view’s frame is visually contiguous with its UIWindow’s top, then it draws its navigation bar with a height of 64 points. If its view’s top is not contiguous with the UIWindow’s top (even if off by only one point), then it draws its navigation bar in the “traditional” way with a height of 44 points. This logic is performed by UINavigationController even if it is several children down inside the view controller hierarchy of your application. There is no way to prevent this behavior.
意思就是UINavigationBar的高度会自行调整为44或者64，没有确定的预测方法。而之前作为UINavigationBar背景的图片是44高度的。最后换了张64高度，上面留了20px透明的图片搞定
网友还有一种解决办法
IOS7的视图有个边缘延伸的属性：edgesForExtendedLayout，
其默认值是UIExtendedEdgeAll。
只要将其改成UIExtendedEdgeNone即可，要注意的是在IOS7以下版本会出现bug。
所以在UIViewController 的viewDidLoad里加上下面代码就完美解决了这个问题
if( ([[[UIDevicecurrentDevice] systemVersion] doubleValue]>=7.0)) {
self.edgesForExtendedLayout = UIRectEdgeNone;
self.extendedLayoutIncludesOpaqueBars = NO;
self.modalPresentationCapturesStatusBarAppearance = NO;
}
