How to get a bar button item to update based on user cell taps

Question

I am creating a quiz app where each question in the quiz is presented by a tableview embedded in a navigationcontroller. I have a score label set in the right bar button item of the navigation controller that I want to update each time a user chooses an answer (tableviewcells). I can't seem to get the score label to update with my code.. Any thoughts?

Btw there is more stuff in my viewDidLoad but i just kept the relevant stuff in for the code snippet.

var score: Int = 0 {
     didSet {
          navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Score: \(score)", style: .plain, target: nil,
          action: Selector(("updateScore")))
     }
}

override func viewDidLoad() {
     super.viewDidLoad()

     score = 0
}

@objc func updateScore() {
     var newScore = score
     for question in questionsList {
          if question.selectedAnswerIndex == question.correctAnswerIndex {
               newScore += 1
          }
     }

     score = newScore

}

Also the selectedAnswerIndex and correctAnswerIndex comes from my question model class that contains the quiz questions in my questionsList array. Is this possible to do with a bar button item or should I be looking into other ways to represent the score..?

UIKit

1.5k

Posted by

JLago

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Answer 1

You create a new instance of navigationItem.rightBarButtonItem each time you change the value.

You should just upfdate the existing navigationItem.rightBarButtonItem

Posted by

Claude31

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Answer 2

I'm a little confused. Isn't the updateScore method updating the existing rightBarButtonItem? How do I change my code so it doesn't create a new instance of rightBarButton each time?

Posted by

JLago

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Answer 3

You can try something like this:

    var score: Int = 0 {
        didSet {
            navigationItem.rightBarButtonItem?.title = "Score: \(score)"
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Score: \(score)", style: .plain,
            target: self, action: #selector(updateScore))
    }

As far as I tested with iOS 12.4 simulator in Xcode 10.3, the title of the right bar button item is updated each time `score` is set.

But I am not sure if this is the right way, as the doc says

Discussion

You should set this property before adding the item to a bar. The default value is

nil

.

or should I be looking into other ways to represent the score..?

Maybe you should.

Some points:

- When you set target as nil, no action will be performed

- Do not use the initializer of `Selector`, such as `Selector(("..."))`, use `#selector` as far as possible

Posted by

OOPer

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Answer 4

No, you are not just updating.

When you call

navigationItem.rightBarButtonItem = UIBarButtonItem

you create a new instance.

You have to change the title of the existing item, not create a new one.

Posted by

Claude31

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How to get a bar button item to update based on user cell taps

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