Today I came across a small issue when trying to adjust a UIView based on rotation of the device. The UINavigationController has two main delegate methods that pertain to rotation of the device: willRotateToInterfaceOrientation:duration: and didRotateFromInterfaceOrientation:. They are pretty self-explanatory. The former is called when the view is about to rotate, and provides the destination rotation. The latter is called when the view rotation animation is over.

The problem I have is that I want to wait until the rotation is over so that I can query the UIViewController’s view for its size and then update subviews accordingly. But if we wait until the didRotateFromInterfaceOrientation: method is called, the entire rotation animation is over and then all my views update – it’s pretty jerky. But if I perform my view manipulation in the willRotate... method, the view controller’s view has not been assigned its new view container yet, so I don’t know what the new size of the view is.

I originally thought there might be a function that allows me to ask the view controller what its size will be for a particular rotation, but I couldn’t find this anywhere in the docs. As it turns out, there is a third delegate method that does exactly what I want. According to this Stack Overflow response, when the willAnimateRotationToInterfaceOrientation:duration: method is called, the view controller’s view has already been assigned its destination view container and the animation is about to start. If I perform my view manipulation then, I know what the view size is about to be, and any changes I make occur at the same time as the actual rotation of the view. It is a small and easy modification, but makes a big difference.