原文：When does layoutSubviews get called?
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.
。init does not cause layoutSubviews to be called (duh)
初始化时不会调用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
[view addSubview:subView]会使view，subView和view的所有子view都调用layoutSubviews
。setFrame intelligently calls layoutSubviews on the view having it’s frame set only if the size parameter of the frame is different
setFrame,只有当改变frame的frame.size并且改变前后的size大小不一样时会调用layoutSubviews,改变frame.origin不会调用layoutSubviews
。scrolling a UIScrollView causes layoutSubviews to be called on the scrollView, and it’s superview
滑动UIScrollView会使该scrollview和它的父视图调用layoutSubviews
。rotating a device only calls layoutSubview on the parent view (the responding viewControllers primary view)
旋转设备只会使父视图调用layoutSubviews
。removeFromSuperview – layoutSubviews is called on superview only
removeFromSuperview只会是父视图调用layoutSubviews
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