edgesForExtendedLayout

ios默认viewController的View会延伸到最顶端，即使上面有导航条、状态栏，可以设置edgesForExtendedLayout属性

f([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0){
        
        self.edgesForExtendedLayout = UIRectEdgeNone;
        self.automaticallyAdjustsScrollViewInsets = NO;
        
    }