Rotation methods deprecated, equivalent of 'didRotateFromInterfaceOrientation'?

Okay found it, just have to use the animateAlongsideTransition:completion: method on the passed UIViewControllerTransitionCoordinator.

- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator
{   
    [coordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context)
    {
        UIInterfaceOrientation orientation = [[UIApplication sharedApplication] statusBarOrientation];
        // do whatever
    } completion:^(id<UIViewControllerTransitionCoordinatorContext> context)
    { 

    }];

    [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
}

The Swift Version of the answer by strange

override func viewWillTransitionToSize(size: CGSize, withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator) {

    coordinator.animateAlongsideTransition({ (UIViewControllerTransitionCoordinatorContext) -> Void in

        let orient = UIApplication.sharedApplication().statusBarOrientation

        switch orient {
        case .Portrait:
            println("Portrait")
            // Do something
        default:
            println("Anything But Portrait")
            // Do something else
        }

        }, completion: { (UIViewControllerTransitionCoordinatorContext) -> Void in
            println("rotation completed")
    })

    super.viewWillTransitionToSize(size, withTransitionCoordinator: coordinator)
}

iOS 10.3 & Swift 3

override func willTransition(to newCollection: UITraitCollection, with coordinator: UIViewControllerTransitionCoordinator) {

        coordinator.animate(alongsideTransition: { (_) in
            let orient = newCollection.verticalSizeClass

            switch orient {
            case .compact:
                print("Lanscape")///Excluding iPads!!!

            default:
                print("Portrait")
            }
        }, completion: { _ in
            print("rotation completed")
        })

        super.willTransition(to: newCollection, with: coordinator)
    }

The accepted answer in Swift 3:

override func willTransition(to newCollection: UITraitCollection, with coordinator: UIViewControllerTransitionCoordinator) {
    coordinator.animate(alongsideTransition: { (_) in
        let orient = UIApplication.shared.statusBarOrientation

        switch orient {
        case .portrait:
            print("Portrait")
        // Do something
        default:
            print("Anything But Portrait")
            // Do something else
        }
    }, completion: { (UIViewControllerTransitionCoordinatorContext) -> Void in
      print("rotation completed")
    })

    super.willTransition(to: newCollection, with: coordinator)
}

It works fine for me 👍