UIalertController before segue

Question

I want to go to the former page by using this code but I can't. Appreciate if you give me an answer!!

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {

if segue.identifier == "edit"{


    let destViewController = segue.destinationViewController as! ScoreBoardVC

    let indexPath = self.tableView.indexPathForSelectedRow!
    destViewController.matches = matches[indexPath.row]



    let alertView = UIAlertController(title: "Want to edit?", message: "Keep in mind the date!", preferredStyle: UIAlertControllerStyle.Alert)
    alertView.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil))

   presentViewController(alertView, animated: true, completion: nil)


}



}

score 0 · Answer 1 · edited May 23 '17 at 12:08

The sourceViewController is likely to be exiting the view hierarchy after a segue, so if a controller is presented there, it will be dismissed immediately.

The destinationViewController may not be present in the view hierarchy by prepareForSegue there, so if you present it there, you may get

2016-08-23 10:22:22.354 Foo[589:137407] Warning: Attempt to present <UIAlertController: 0x17eb0e00> on <Foo.DestinationViewController: 0x177e7b60> whose view is not in the window hierarchy!

2016-08-23 10:22:22.904 Foo[589:137407] Attempting to load the view of a view controller while it is deallocating is not allowed and may result in undefined behavior (<UIAlertController: 0x17eb0e00>)

One possibility is to add an ivar onto your destinationViewController like so.

class DestinationViewController: UIViewController {
    var presentWhenAppearing: UIViewController? = nil

    override func viewWillAppear(animated: Bool) {
        if let p = presentWhenAppearing {
            self.presentViewController(p, animated: true, completion: nil)
            presentWhenAppearing = nil
        }
    }
}

which can then be used inside prepareForSegue as follows

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "myIdentifier" {

        guard let destinationVC = segue.destinationViewController as? DestinationViewController else {
            fatalError("Unexpected VC")
        }

        let alert = UIAlertController(title: "You are currently offline", message: "but your download willl be begin and continue when you have an internet connection.", preferredStyle: .Alert)
        alert.addAction(UIAlertAction(title: "OK", style: .Default, handler: nil))
        destinationVC.presentWhenAppearing = alert

    }
}

See also How to present UIAlertController when not in a view controller? for other answers that might work here.

UIalertController before segue

1 Answers1