- init does not cause layoutSubviews to be called (duh)
init方法不会触发
- addSubview: causes layoutSubviews to be called on the view being added, the view it’s being added to (target view), and all the subviews of the target
addSubview在目标视图被添加子视图的时候触发
- view setFrame intelligently calls layoutSubviews on the view having its frame set only if the size parameter of the frame is different
view的frame发生变化的时候触发
- scrolling a UIScrollView causes layoutSubviews to be called on the scrollView, and its superview
scrollview和它的父视图滚动的时候触发
- rotating a device only calls layoutSubview on the parent view (the responding viewControllers primary view)
转旋设备的时候，相应的视图控制器对应的主视图会触发
- Resizing a view will call layoutSubviews on its superview
改变视图大小的时候会在视图的父视图上触发
