edgesForExtendedLayout

ios默认viewController的View会延伸到最顶端，即便上面有导航条、状态栏，能够设置edgesForExtendedLayout属性

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