Swift UIAlertController -> ActionSheet iPad iOS8 Crashes

try this

alertController.popoverPresentationController?.sourceView = self.view

If you want to present it in the centre with no arrows on iPads [Swift 3+]:

    if let popoverController = alertController.popoverPresentationController {
        popoverController.sourceView = self.view
        popoverController.sourceRect = CGRect(x: self.view.bounds.midX, y: self.view.bounds.midY, width: 0, height: 0)
        popoverController.permittedArrowDirections = []
    }
    self.present(alertController, animated: true, completion: nil)

Nate Cook is totally right however I would do it so I detect if it is iPad or iPhone.

This is for barButtonItem:

if ( UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiom.pad ){

            if let currentPopoverpresentioncontroller = alertController.popoverPresentationController{
                currentPopoverpresentioncontroller.barButtonItem = sender as! UIBarButtonItem
                currentPopoverpresentioncontroller.permittedArrowDirections = UIPopoverArrowDirection.down;
                self.present(alertController, animated: true, completion: nil)
            }
        }else{
            self.present(alertController, animated: true, completion: nil)
        }

The error message is telling you that you need to give the alert controller's popoverPresentationController a location so that it can position itself properly. This is easy to do -- just check to see if there's a popover controller and add the sender as the source.

If your button is a UIBarButtonItem:

if let popoverController = alertController.popoverPresentationController {
    popoverController.barButtonItem = sender
}
self.presentViewController(alertController, animated: true, completion: nil)

Otherwise:

if let popoverController = alertController.popoverPresentationController {
    popoverController.sourceView = sender
    popoverController.sourceRect = sender.bounds
}
self.presentViewController(alertController, animated: true, completion: nil)