iOS how to detect programmatically when top view controller is popped?

Question

Suppose I have a nav controller stack with 2 view controllers: VC2 is on top and VC1 is underneath. Is there code I can include in VC1 that will detect that VC2 has just be

Answer 1

This is worked for me

UIViewController *fromViewController = [[[self navigationController] transitionCoordinator] viewControllerForKey:UITransitionContextFromViewControllerKey];
if (![[self.navigationController viewControllers] containsObject:fromViewController] && !self.presentedViewController)
{
  //Something is being popped and we are being revealed 
}