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Summary:
Typically, when a container view controller resizes one of its child view controllers, it will call viewWillTransitionToSize:withTransitionCoordinator: to let it know that it will be resized. This allows the child view controller to respond appropriately to the change in size, including animating any necessary changes.

A UISplitViewController is a container view controller. When you change its preferredPrimaryColumnWidthFraction property, it can resize its child view controllers. However, even when it does resize its children, it does not call viewWillTransitionToSize:withTransitionCoordinator:. This makes adjusting to the new size much more difficult. E.G. in my case, I have a UIScrollView whose x contentOffset I need to adjust according to the size of the master view controller's view.

Steps to Reproduce:
Look at the sample project attached.

Alternatively:
1. Create a UISplitViewController
2. Implement viewWillTransitionToSize:withTransitionCoordinator: in your master view controller
3. Create a way to change the preferredPrimaryColumnWidthFraction property on the split view controller
4. Observe that viewWillTransitionToSize:withTransitionCoordinator: doesn't get called on your master view controller (nor on your detail view controller for that matter)

Expected Results:
viewWillTransitionToSize:withTransitionCoordinator: should be called with the new size.

Actual Results:
viewWillTransitionToSize:withTransitionCoordinator: is never called

Version:
iOS 8.1.3 (12B466) - iOS 8.2 beta 5 (12D5480a)

Notes:


Configuration:
Any device that supports an expanded UISplitViewController

Attachments:
'TestSplitResizing.zip' was successfully uploaded.