UIAlertController在呈现之前已释放

Question

I want to make a "rate app" alert, but for some reason it gets deallocated before showing it.

Here's the code:

func showAlert() {
    if #available(iOS 8.0, *)
    {
        let alertController = UIAlertController(title: "Rate App", message: "Rate this app now", preferredStyle: .Alert)
        let neverAction = UIAlertAction(title: "Never Show This Again", style: .Destructive, handler: { (action: UIAlertAction) in
            self.userDefaults.setBool(true, forKey: "rateAlertRejected")
        })
        let rateAction = UIAlertAction(title: "Rate Now", style: .Default, handler: { (action: UIAlertAction) in
            // Rate App
        })
        let remindAction = UIAlertAction(title: "Remind Me Later", style: .Cancel, handler: nil)

        alertController.addAction(rateAction)
        alertController.addAction(neverAction)
        alertController.addAction(remindAction)

        presentViewController(alertController, animated: true, completion: nil)
    }
    else
    {
        // Identical code (using UIAlertView) for iOS 7 which works perfectly
    }
}

The method executes (in certain conditions, but for testing purposes it does it every time) after a custom unwind segue.

Why do I have this problem? I used UIAlertController before but I had no issues.

Answer 1

According to your comment you show showAlert in a method that executes after a custom unwind segue.

unwind segue dismisses the view heriarchy and therefore your alert does not get reference to a view controller to show from.

To solve this, show your alert in the View controller you unwind to or wait for the alert controller action to be completed before unwinding.