UIAlertAction handler

Question

Created Nov ’20

Replies 4

Boosts 0

Views 2.6k

Participants 3

I am writing UIAlert and UIAlertAction and I want to add performSeque to handler in UIAlertAction but I keep getting this error: "Cannot use instance member 'performSegue' within property initializer; property initializers run before 'self' is available"

here is my code

Code Block let alert = UIAlertController(title: "Title", message: "Message", preferredStyle: .alert)
  
let action = UIAlertAction(title: "Title", style: .default, handler: { action in
    performSegue(withIdentifier: "goToVC", sender: nil)
  })

Answered by Claude31 in 645082022

If I need to have alert as a class property, I then declare it as

Code Block var alert : UIAlertController?

and initialize in viewDidLoad.

Otherwise, I do as OOPer described it.

Boost

Answer 1

OOPer OP

Nov ’20

Seems you have written your code right under the class definition as property declaration.
You need to move it into some instance method.

Code Block class YourViewController: UIViewController {
    //Do not put the code directly under the class:
    //let alert = UIAlertController(title: "Title", message: "Message", preferredStyle: .alert)
    //let action = UIAlertAction(title: "Title", style: .default, handler: { action in
    //    performSegue(withIdentifier: "goToVC", sender: nil)
    //})
    func someMethod() {
        //...
        //Put the code in a method:
        let alert = UIAlertController(title: "Title", message: "Message", preferredStyle: .alert)
        let action = UIAlertAction(title: "Title", style: .default, handler: { action in
            performSegue(withIdentifier: "goToVC", sender: nil)
        })
        //...
    }
    //...
}

0

Answer 2

Claude31 OP

Nov ’20

Accepted Answer

If I need to have alert as a class property, I then declare it as

Code Block var alert : UIAlertController?

and initialize in viewDidLoad.

Otherwise, I do as OOPer described it.

0

Answer 3

sebko_chlapec OP

Nov ’20

Okay so first of all sorry, sorry I put the checkmark by mistake 😅 and when I put the alert and action in viewDidLoad() I get that yellow triangle saying this for alert "Initialization of immutable value 'alert' was never used; consider replacing with assignment to '' or removing it", and for action "Initialization of immutable value 'action' was never used; consider replacing with assignment to '' or removing it". I tried both ways and it always showed up.

Sorry if my questions and answers are weird I'm new to this and still learning

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Answer 4

OOPer OP

Nov ’20

I put the alert and action in viewDidLoad()

Never put such code in viewDidLoad(), you instantiate UIAlertController just before you present it. Do not have it as a property.

If you want to reduce some lines for repeatedly used alerts, you should create a method, not a property.

Code Block class ViewController: UIViewController {
    //...
    func createTheAlert() -> UIAlertController {
        let alert = UIAlertController(title: "Title", message: "Message", preferredStyle: .alert)
          
        let action = UIAlertAction(title: "Title", style: .default, handler: { action in
            self.performSegue(withIdentifier: "goToVC", sender: nil)
          })
        
        alert.addAction(action)
        
        //...
        
        return alert
    }
    @IBAction func someActionMethod(_ sender: Any) {
        //...
        let alert = createTheAlert()
        present(alert, animated: true, completion: nil)
    }
    @IBAction func anotherActionMethod(_ sender: Any) {
        //...
        let alert = createTheAlert()
        present(alert, animated: true, completion: nil)
    }
    
    //...
}

If you do not want to make your questions misunderstood, you should better include enough code. Exactly the same lines will work in some place and some context, but they will not in other cases. At least, full method including the lines.

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