iOS 7中，苹果引入了一个新的属性，叫做[UIViewController setEdgesForExtendedLayout:]，它的默认值为UIRectEdgeAll。当你的容器是navigation controller时，默认的布局将从navigation bar的顶部开始。这就是为什么所有的UI元素都往上漂移了44pt。有时会加上顶部tool bar的高度 20, 20+44 = 64
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.
if (OSVersionIsAtLeastiOS7()) {
if ([self respondsToSelector:@selector(edgesForExtendedLayout)])
{
self.edgesForExtendedLayout = UIRectEdgeNone;
}
}
