Some of the points in BadPirate's answer are only partially true:
For addSubView
point
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.
It depends on the view's (target view) autoresize mask. If it has autoresize mask ON, layoutSubview will be called on each addSubview
. If it has no autoresize mask then layoutSubview will be called only when the view's (target View) frame size changes.
Example: if you created UIView programmatically (it has no autoresize mask by default), LayoutSubview will be called only when UIView frame changes not on every addSubview
.
It is through this technique that the performance of the application also increases.
For the device rotation point
Rotating a device only calls layoutSubview on the parent view (the responding viewController's primary view)
This can be true only when your VC is in the VC hierarchy (root at window.rootViewController
), well this is most common case. In iOS 5, if you create a VC, but it is not added into any another VC, then this VC would not get any noticed when device rotate. Therefore its view would not get noticed by calling layoutSubviews.