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iOS

Posted by Adrian Evensen
Adrian Evensen
1,078 Points

Assigning a struct instance to UILabel

Hello!

I keep getting errors with my code when trying to chance an UILabel with a text string

First I created a struct:

        struct Question {
             var  question : String?
             var  answer : String?
         }

Then made a instance of the struct:

         var questionsArray = [Question]()

Then made a few test-purpose-only questions inside viewDidLoad: 

        questionsArray = [Question(question: "2 + 2", answer: "4"),

        Question(question: "2 + 3", answer: "5"),

        Question(question: "2 + 4", answer: "6"),

        Question(question: "2 + 5", answer: "7"),

        Question(question: "2 + 6", answer: "8"),

        Question(question: "2 + 7", answer: "9"),

        Question(question: "2 + 8", answer: "10")]

Then I made a func that should change the UILabel.text, as the level int increases each time the user types in the right answer: 

    func displayQuestion() {

    if questionLabel.text == questionsArray[level].question {
        //Do Nothing
    } else {
        //Display or update the question
        questionLabel.text = questionsArray[level].question
    }

And ofcoure, I added an 

   displayQuestion()

inside the viewDidLoad after the questions to start the function

No errors, and I feel like the code should be safe and actually work, but when I try to build the app in the simulator I keep getting "fatal error: unexpectedly found nil while unwrapping an Optional value" error.

Can you see any mistakes or some code that causes the app to crash?

Thanks!

1 Answer

jcorum
jcorum
71,830 Points
jcorum
jcorum
71,830 Points

Adrian, you define question as a String optional

var question: String?

but then in this statement:

questionLabel.text = questionsArray[level].question

you return a question (an optional) without unwrapping it.

Here's your code modified to run in a playground:

        struct Question {
            var  question : String?
            var  answer : String?
        }

        var questionsArray = [Question]()

        questionsArray = [Question(question: "2 + 2", answer: "4"),

            Question(question: "2 + 3", answer: "5"),

            Question(question: "2 + 4", answer: "6"),

            Question(question: "2 + 5", answer: "7"),

            Question(question: "2 + 6", answer: "8"),

            Question(question: "2 + 7", answer: "9"),

            Question(question: "2 + 8", answer: "10")]

        var text = ""

        func displayQuestion() {

            if text == questionsArray[0].question! {
                //Do Nothing
            } else {
                //Display or update the question
                text = questionsArray[1].question!
            }
        }

        displayQuestion()

Here forcibly unwrapping works (and I used it just to make the point) because your data is complete, but in general it's a bad idea and one should use if let or guard to be safe!!