How to detect when a popover is dismissed in iOS 9

The updated answer for this issue.

All credit to this answer:

The method you must use on iOS 13: - (void)presentationControllerDidDismiss:(UIPresentationController *)presentationController

Not sure which method you're referring to as being deprecated but you can still use the UIPopoverPresentationControllerDelegate to achieve this. Something like:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "popoverSegue" {
        let vc = segue.destinationViewController
        sortVC.modalPresentationStyle = .Popover
        sortVC.popoverPresentationController?.sourceRect = filterButton.bounds
        sortVC.preferredContentSize = CGSizeMake(216, 150)
        sortVC.popoverPresentationController!.delegate = self
    }
}

And then use the

func popoverPresentationControllerDidDismissPopover(popoverPresentationController: UIPopoverPresentationController)

method to handle its dismissal.

The popoverControllerDidDismissPopover: method has been replaced by popoverPresentationControllerShouldDismissPopover: because UIPopoverControllerDelegate has been replaced by the UIPopoverPresentationControllerDelegate.

From your presenting view controller, conform to the new protocol and set the delegate for the popover presentation controller in prepareForSegue::

class MyPresentingViewController: UIViewController, UIPopoverPresentationControllerDelegate {

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {         
        if let popoverPresentationController = segue.destinationViewController.popoverPresentationController {
            popoverPresentationController.delegate = self
        }
    }

    func popoverPresentationControllerShouldDismissPopover(popoverPresentationController: UIPopoverPresentationController) -> Bool {
        return true
    }
}

You can then use the delegate method to handle detection of the dismissal in the way that you were previously intending.