layout用法

It’s important to optimize any UIView layoutSubviews method you create, as it can be frequently called, and has the potential for creating recursion (triggering a setNeedsLayout from layoutSubviews can create a loop that will grossly affect your apps performance). Layout subviews is called once per run loop on any view that has had setNeedsLayout or setNeedsDisplayWithRect: called on it. So in addition to any time you manually call these methods, it can be useful to know when the UI framework calls setNeedsLayout/setNeedsDisplay as this will trigger layoutSubviews.

For this purpose, I will define a few view relationships:

  • View1 – UIView class, root view for examples
  • View1.1 – UIScrollView class, subview of View1
  • View1.1.1 – UIView class, subview of View1.1 (No autoresize mask)
  • View1.1.2 – UIView class, another subview of View1.1 (Autoresize mask – flexible width)

I then ran the following tests.  An X means the view was layed out


From this I surmise the following:

  • init does not cause layoutSubviews to be called (duh)
  • init 方法不会调用layoutSubviews
  • 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 view
  • addSubview会调用 subview窗体,subview父窗体,和subview窗体下的所有子窗体 中的layoutSubviews
  • setFrame intelligently calls layoutSubviews on the view having it’s frame set only if the size parameter of the frame is different
  • setFrame中的参数变化的时候会调用layoutSubviews
  • scrolling a UIScrollView causes layoutSubviews to be called on the scrollView, and it’s superview
  • 滚动UIScrollView会调用 scrollview,scrillview的父窗体 的layoutSubviews方法
  • rotating a device only calls layoutSubview on the parent view (the responding viewControllers primary view)
  • 旋转设备时候在 父窗体 会被调用
  • removeFromSuperview – layoutSubviews is called on superview only (not show in table)

Hopefully this is helpful information for you as well.


1 comment:

I find that resizing (not moving, only resizing) any subview causes the superview to get -layoutSubviews sent to it, which I found unexpected. From your table it doesn’t look like you tested that case.

posted @ 2011-11-04 12:09  KID  阅读(452)  评论(0编辑  收藏  举报