iOS edgesForExtendedLayout

 self.navigationController.navigationBar.barStyle = UIBarStyleDefault;

    self.navigationController.navigationBar.translucent= NO;    

    self.edgesForExtendedLayout = UIRectEdgeAll;

    self.extendedLayoutIncludesOpaqueBars = YES;

 

对于viewcontroller是否充navi的顶部开始布局，取决于两个属性edgesForExtendedLayout， extendedLayoutIncludesOpaqueBars（当navigationController.navigationBar.translucent= NO）时会用到！