AlertController is not in the window hierarchy

Question

I\'ve just created a Single View Application project with ViewController class. I would like to show a UIAlertController from a function which is located inside my own class

Answer 1

Here is the code of an UIAlertController in a Utility.swift class (not a UIViewController) in Swift3, Thanks Mitsuaki!

private func presentViewController(alert: UIAlertController, animated flag: Bool, completion: (() -> Void)?) -> Void {
    UIApplication.shared.keyWindow?.rootViewController?.present(alert, animated: flag, completion: completion)
}
func warningAlert(title: String, message: String ){
    let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.alert)
    alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.default, handler:  { (action) -> Void in
    }))        
 //   self.present(alert, animated: true, completion: nil)
    presentViewController(alert: alert, animated: true, completion: nil)
}

Answer 2

Write the following 3 lines, all we need to do is this.

Swift 3.0

private func presentViewController(alert: UIAlertController, animated flag: Bool, completion: (() -> Void)?) -> Void {
     UIApplication.shared.keyWindow?.rootViewController?.present(alert, animated: flag, completion: completion)
  }

Swift 2.0

  private func presentViewController(alert: UIAlertController, animated flag: Bool, completion: (() -> Void)?) -> Void {
     UIApplication.sharedApplication().keyWindow?.rootViewController?.presentViewController(alert, animated: flag, completion: completion)
  }

Answer 3

If you want to create a separate class for displaying alert like this, subclass NSObject not UIViewController.

And pass the ViewControllers reference from which it is initiated, to the showAlert function so that you can present alert view there.

Answer 4

It helped me to stick a slight delay between the viewDidLoad method and firing the alert method:

   [self performSelector:@selector(checkPhotoPermission) withObject:nil afterDelay:0.1f];

Answer 5

This worked for me:

- (UIViewController *)topViewController{
  return [self topViewController:[UIApplication sharedApplication].keyWindow.rootViewController];
}

- (UIViewController *)topViewController:(UIViewController *)rootViewController
{
  if (rootViewController.presentedViewController == nil) {
    return rootViewController;
  }

  if ([rootViewController.presentedViewController isMemberOfClass:[UINavigationController class]]) {
    UINavigationController *navigationController = (UINavigationController *)rootViewController.presentedViewController;
    UIViewController *lastViewController = [[navigationController viewControllers] lastObject];
    return [self topViewController:lastViewController];
  }

  UIViewController *presentedViewController = (UIViewController *)rootViewController.presentedViewController;
  return [self topViewController:presentedViewController];
}

Implementation:

UIViewController * topViewController = [self topViewController];

Using with alert:

[topViewController presentViewController:yourAlert animated:YES completion:nil];

You can send an alert from any class in your app (that uses UIKit: #import <UIKit/UIKit.h> )

Source here.

Answer 6

If you're instancing your UIAlertController from a modal controller, you need to do it in viewDidAppear, not in viewDidLoad or you'll get an error.

Here's my code (Swift 4):

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

    let alertController = UIAlertController(title: "Foo", message: "Bar", preferredStyle: .alert)

    alertController.addAction(UIAlertAction(title: "OK", style: .cancel, handler: nil))
    present(alertController, animated: true, completion: nil)
}