如何使用 UIAlertController

Question

I am trying to use this code in a Pacman game I got from some website but had to change UIAlertView to UIAlertController except the following code has two errors that I don't know how to fix (I am really new to programming and feel like this is a really newbie question - sorry!!)

The first error is in line 4: No known class method for selector alertControllerWithTitle

A second error is in the last line: no visible interface declares the selector show

- (void)collisionWithExit: (UIAlertController *)alert {

    if (CGRectIntersectsRect(self.pacman.frame, self.exit.frame)) {

        [self.motionManager stopAccelerometerUpdates];

        UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Congratulations"
                                                        message:@"You've won the game!"
                                                       delegate:self
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:nil
                                              preferredStyle:UIAlertControllerStyleAlert];
        [alert show];
    }
}

Answer 1

Please check the following code:

UIAlertController* alert = [UIAlertController alertControllerWithTitle:@"My Alert"
                           message:@"This is an alert."
                           preferredStyle:UIAlertControllerStyleAlert];

UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault
                               handler:^(UIAlertAction * action) {}];

[alert addAction:defaultAction];
[self presentViewController:alert animated:YES completion:nil];

Answer 2

Check below this code.

for Objective-C:

UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Alert" message:@"Message" preferredStyle:UIAlertControllerStyleAlert];

UIAlertAction *ok = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
                        //button click event
                    }];
UIAlertAction *cancel = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:nil];
[alert addAction:cancel];
[alert addAction:ok];
[self presentViewController:alert animated:YES completion:nil];

for Swift 4.x:

let alert = UIAlertController(title: "Alert", message: "Message", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "OK", style: .default, handler: { action in
  switch action.style {
  case .default:
    print("default")
  case .cancel:
    print("cancel")
  case .destructive:
    print("destructive")
  }
}))
self.present(alert, animated: true, completion: nil)

Answer 3

Swift 5: Simple Extension

extension UIViewController {

    func presentAlert(withTitle title: String, message : String, actions : [String: UIAlertAction.Style], completionHandler: ((UIAlertAction) -> ())? = nil) {

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

        for action in actions {

            let action = UIAlertAction(title: action.key, style: action.value) { action in

                if completionHandler != nil {
                    completionHandler!(action)
                }
            }

            alertController.addAction(action)
        }

        self.present(alertController, animated: true, completion: nil)
    }
}

Usage:

self.presentAlert(withTitle: "Network Error", message: "Please check your internet connection", actions: [
    "Retry" : .default, "Cancel": .destructive] , completionHandler: {(action) in

        if action.title == "Retry" {
            print("tapped on Retry")

        }else if action.title == "Cancel" {
            print("tapped on Cancel")
        }
})

OR

self.presentAlert(withTitle: "Mail services are not available", message: "Please Configure Mail On This Device", actions: ["OK" : .default] , completionHandler: nil)