How to fix 'Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value' in Swift

Question

I'm trying to make an IOS Unit Converter app using swift. But I'm getting an exception when a textfield is empty after entering some value.

I've already tried to solve the problem with 'if let' and 'guard statement' but could not get it to work maybe I did something wrong somewhere.


class ViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var textOunce: UITextField!
    @IBOutlet weak var textPound: UITextField!
    @IBOutlet weak var textGram: UITextField!
    @IBOutlet weak var textStone: UITextField!
    @IBOutlet weak var textStonePound: UITextField!
    @IBOutlet weak var textKg: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        textOunce.delegate = self
        textPound.delegate = self
        textGram.delegate = self
        textStone.delegate = self
        textStonePound.delegate = self
        textKg.delegate = self

        textOunce.addTarget(self, action: #selector(self.textFieldDidChange(_:)), for: .editingChanged)
        textPound.addTarget(self, action: #selector(self.textFieldDidChange(_:)), for: .editingChanged)
        textGram.addTarget(self, action: #selector(self.textFieldDidChange(_:)), for: .editingChanged)
        textStone.addTarget(self, action: #selector(self.textFieldDidChange(_:)), for: .editingChanged)
        textStonePound.addTarget(self, action: #selector(self.textFieldDidChange(_:)), for: .editingChanged)
        textKg.addTarget(self, action: #selector(self.textFieldDidChange(_:)), for: .editingChanged)
    }

    @objc func textFieldDidChange(_ textField: UITextField) {

        var toOunce = Double(textOunce.text!)!
        toOunce = toOunce / 16
        textPound.text = "\(toOunce)"

    }

}

I want to dynamically fill the other textfields when the user enters a value on a textfield and set the value to zero instead of throwing a nil exception if the user decides to erase all the values they entered in a textfield.

Remove the last `!` from `Double(textOunce.text!)!`, then check whether the result is nil. — Phillip Mills, Mar 31 '19 at 16:33
It works! How do you set the value of the textfields to zero if the user deletes the values in the textfield? — Tom Fitzburgh, Mar 31 '19 at 16:40
Great to know that. Can you accept my answer and upvote so that my answer helps others too :) — Amir Khan, Mar 31 '19 at 16:44
I managed to get the fields empty. Thank you so much for your help! :D — Tom Fitzburgh, Mar 31 '19 at 17:00
Amazing @TomFitzburgh, You can achieve by using `textFieldShouldReturn` or `textFieldDidEndEditing`. Actually I'm trying to modified `textFieldDidChange` but it's going quite messy though. Anyway Happy coding and keep posting if you are having any issue :) — Amir Khan, Mar 31 '19 at 17:02

Amir Khan · Accepted Answer · 2019-03-31T17:17:15.250

You need to check whether inputed data is in double format or can it be converted to Double if yes, then if part will be executed otherwise it will goes inside else part.

Replace textFieldDidChange method with below -

 @objc func textFieldDidChange(_ textField: UITextField) {

    if var toOunce = Double(textField.text!) {

        toOunce = toOunce / 16
        textPound.text = "\(toOunce)"

    }else{

        debugPrint("Invalid input")
    }

 }

To add 0 if user didn't enter anything or added spaces -

func textFieldShouldReturn(_ textField: UITextField) -> Bool {

    if textField.text?.trimmingCharacters(in: .whitespaces).count  == 0{

      textField.text = "0"
    }

    textField.resignFirstResponder() // This line is important to add text to it. 
    return false // OR true  // Have to pass any value because it needs Bool return.
}

How to fix 'Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value' in Swift

1 Answers1