Как определить момент до поворота экрана и после поворота экрана

viewWillTransitionToSize

- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id <UIViewControllerTransitionCoordinator>)coordinator
{
    [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
    
    [coordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context) {
        
        // Stuff you used to do in willRotateToInterfaceOrientation would go here.
        // If you don't need anything special, you can set this block to nil.
        
    } completion:^(id<UIViewControllerTransitionCoordinatorContext> context) {
        
        // Stuff you used to do in didRotateFromInterfaceOrientation would go here.
        // If not needed, set to nil.
        
    }];
}