Detecting if a view controller is presented in a popover with UITraitCollection

UIPopoverPresentationControllerDelegate.m

- (void)prepareForPopoverPresentation:(UIPopoverPresentationController *)popover
{
  if (!self.adaptivePresentationStyleAsked) {
    popover.overrideTraitCollection = [popover.presentingViewController.traitCollection copy];
  }
}

- (UIModalPresentationStyle)adaptivePresentationStyleForPresentationController:(UIPresentationController *)popover
                                                               traitCollection:(UITraitCollection *)traitCollection
{
  self.adaptivePresentationStyleAsked = YES;
  
  popover.overrideTraitCollection = [traitCollection copy];
  if (traitCollection.horizontalSizeClass == UIUserInterfaceSizeClassCompact ||
      traitCollection.verticalSizeClass == UIUserInterfaceSizeClassCompact) {
    return UIModalPresentationOverFullScreen;
  } else {
    return UIModalPresentationPopover;
  }
}

- (void)presentationController:(UIPresentationController *)popover
  willPresentWithAdaptiveStyle:(UIModalPresentationStyle)style
         transitionCoordinator:(id<UIViewControllerTransitionCoordinator>)transitionCoordinator
{
  [popover.presentedViewController willTransitionToTraitCollection:popover.overrideTraitCollection
                                         withTransitionCoordinator:transitionCoordinator];
}

ViewController.m

- (void)willTransitionToTraitCollection:(UITraitCollection *)newCollection
              withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator
{
  [super willTransitionToTraitCollection:newCollection withTransitionCoordinator:coordinator];
  if (newCollection.horizontalSizeClass == UIUserInterfaceSizeClassCompact ||
      newCollection.verticalSizeClass == UIUserInterfaceSizeClassCompact) {
    // full screen
  } else {
    // popover
  }
}