Question

我想通过使用此代码转到前一页，但我不能。如果你给我一个答案，感激不尽！

覆盖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)


}



}

Answer 1

sourceViewController可能在segue之后退出视图层次结构，因此如果在那里显示控制器，它将立即被解除。

那里的prepareForSegue可能不会在视图层次结构中出现destinationViewController，所以如果你在那里展示它，你可能会得到

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>)

一种可能性就是在你的destinationViewController上添加一个ivar。

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
        }
    }
}

然后可以在prepareForSegue内使用，如下所示

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

    }
}

另请参阅How to present UIAlertController when not in a view controller?以了解可能适用的其他答案。

在segue之前的UIalertController

1 个答案: