試圖在取消分配時加載視圖控制器的視圖…（ <UIAlertController:> ）

Question

我在視圖控制器上遇到了以上錯誤，盡管我在另一個視圖控制器中卻獲得了完全相同的代碼，但在這里我沒有收到錯誤：

override func viewDidAppear(animated: Bool) {

    super.viewDidAppear(animated)

    let alertController = UIAlertController(title: "Title", message: "Message", preferredStyle: .Alert)
    alertController.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil))
    alertController.addAction(UIAlertAction(title: "Settings", style: UIAlertActionStyle.Default, handler:  { 
        action in 
            UIApplication.sharedApplication().openURL(NSURL(string: UIApplicationOpenSettingsURLString)!)
        }
        ))
    if self.presentedViewController == nil{
        self.presentViewController(alertController, animated: true, completion: nil)
    }
}

Answer 1

我最終不得不將alertController聲明為類屬性，然后按如下所示修改viewDidAppear：

override func viewDidAppear(animated: Bool) {

    super.viewDidAppear(animated)

        if self.alertController.actions.count == 0 {
            self.alertController.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil))
            self.alertController.addAction(UIAlertAction(title: "Settings", style: UIAlertActionStyle.Default, handler:  { action in UIApplication.sharedApplication().openURL(NSURL(string: UIApplicationOpenSettingsURLString)!)
                }
                ))
            if self.presentedViewController == nil {
                self.presentViewController(self.alertController, animated: true, completion: nil)
            }
        }
}