关于点击状态栏不返回顶部问题
@property(nonatomic) BOOL scrollsToTop 这个属性在起作用 默认是YES
// When the user taps the status bar, the scroll view beneath the touch which is closest to the status bar will be scrolled to top, but only if its `scrollsToTop` property is YES, its delegate does not return NO from `shouldScrollViewScrollToTop`, and it is not already at the top.
// On iPhone, we execute this gesture only if there's one on-screen scroll view with `scrollsToTop` == YES. If more than one is found, none will be scrolled.
只有当一个主控制器有一个scrollview 并把这个属性设置为yes,其他的scrollview.scrollsToTop = NO 这样才会响应这个事件,原理很简单,如果有2个scrollview,系统根本不知道你需要哪个滚动到最上面!