When is layoutSubviews called?

Question

I have a custom view that\'s not getting layoutSubview messages during animation.

I have a view that fills the screen. It has a custom subview at the bo

Answer 1

Building on the previous answer by @BadPirate, I experimented a bit further and came up with some clarifications/corrections. I found that layoutSubviews: will be called on a view if and only if:

• Its own bounds (not frame) changed.
• The bounds of one of its direct subviews changed.
• A subview is added to the view or removed from the view.

Some relevant details:

• The bounds are considered changed only if the new value is different, including a different origin. Note specifically that is why layoutSubviews: is called whenever a UIScrollView scrolls, as it performs the scrolling by changing its bounds' origin.
• Changing the frame will only change the bounds if the size has changed, as this is the only thing propagated to the bounds property.
• A change in bounds of a view that is not yet in a view hierarchy will result in a call to layoutSubviews: when the view is eventually added to a view hierarchy.
• And just for completeness: these triggers do not directly call layoutSubviews, but rather call setNeedsLayout, which sets/raises a flag. Each iteration of the run loop, for all views in the view hierarchy, this flag is checked. For each view where the flag is found raised, layoutSubviews: is called on it and the flag is reset. Views higher up the hierarchy will be checked/called first.