Swift. Passing persistent data from one View Controller to another and storing within a label array

Question

I am using a segue to go from View Controller 1 to View Controller 2. View Controller 1 has a button that sets the persistent data when it is clicked on:

I declare a global var for user default:

   let userDefault = UserDefaults()

Here is my button to set the user default to a string with text values from labels:

 @IBAction func saving(_ sender: UIButton) {
    let savedText = "Gallon \(gallonTextFieldOutlet.text) is equal to Litre \(litreTextFieldOutlet.text) is equal to Pint \(pintTextFieldOutlet.text)"
    userDefault.setValue(savedText, forKey: "SavedConversion")
}

I then get a reference to View Controller 2 and pass this user default when the user goes from View Controller 1 to View Controller 2 via a segue:

  // in view controller 2: reference to get persistent data
    var volumeDataOne:String?
   // in view controller 2: instantiation of my queue class to use methods
   var queue = Queue<String>()

   // segue action in view controller 1
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "savedVolumeData"
    {
       let historyVC:VolumeHistoryViewController = segue.destination as! VolumeHistoryViewController
        
        if let value = userDefault.value(forKey: "SavedConversion") as? String {
        historyVC.volumeDataOne = value
        }
    }

I get this in the View Controller 2 and I am trying to set this to three labels that I have in this View Controller:

  func DisplayVolumeHistory() {
    
    let labelArray = [volumeDataLabelOutlet, volumeDataLabelTwoOutlet, volumeDataLabelThreeOutlet]

        if let bindingOptional = volumeDataOne
        {
            for index in 0..<labelArray.count
            {
            queue.enqueue(val: bindingOptional)
            labelArray[index]?.text = queue.arr[index]
            }
    }
}

In my specification, I have been told that the data needs to be persistent and that only the last five data can be stored at one time. So I have a class that I have called Queue which is referenced in this function. This function gets called on the viewDidLoad of the View Controller 2.

  override func viewDidLoad() {
    super.viewDidLoad()
    
    //Debug ...
    volumeDataLabelOutlet.text = "na"
    volumeDataLabelTwoOutlet.text = "na 2"
    volumeDataLabelThreeOutlet.text = "na 3"
    //...
    
    DisplayVolumeHistory()
    // Do any additional setup after loading the view.
}

I have tested my Queue class in a Playground and it works as expected. The Queue class can be seen here:

class Queue {

var arr = [T]()

func enqueue(val: T){
    if(arr.count < 3) {
        arr.append(val)
    } else {
        for i in 0..<arr.count-1 {
            arr[i] = arr[i + 1]
        }
        arr[arr.count - 1] = val
    }
}

func dequeue() -> (T?){
    if (arr.isEmpty){
        return nil
    } else {
        return arr.remove(at: 0)
    }
}
}

Here is my issue that I cannot seem to figure out. In View Controller 2, all of the three labels will have persistent data, but they will all be of the same data,

For example, if I have data as follows:

DATA 1: 555
DATA 2: 700
DATA 3: 62

I would want:

LABEL 1 --> 555
LABEL 2 --> 700
LABEL 3 --> 62

However, currently it will be:

LABEL 1 --> 62
LABEL 2 --> 62
LABEL 3 --> 62

I am unsure as to why debugging. I believe it is because my persistent data in my View Controller 1 is only taking a string, which the Dictionary is overriding as I use the same key.

However, I looked at the documentation and trying to use a user default array did not solve my issue and I am unsure as to what is causing this problem.

I appreciate any guidance and help to try to solve this issue.

Thanks

Answer 1

You are right on your comment,

which the Dictionary is overriding as I use the same key

Each time you tap that button, you are overriding the value with the new one. So you should be seeing always on your v2, the last one.

So probably you should store an array instead of a String.

    //on v1
    var values = [String]()

    @IBAction func saving(_ sender: UIButton) {
        let savedText = "Gallon \(gallonTextFieldOutlet.text) is equal to Litre \(litreTextFieldOutlet.text) is equal to Pint \(pintTextFieldOutlet.text)"
        values.append(savedText)
        UserDefaults.standard.setValue(values, forKey: "SavedConversion") 
    }

You will pass it to v2 as you are doing now

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "savedVolumeData"
    {
       let historyVC:VolumeHistoryViewController = segue.destination as! VolumeHistoryViewController
        
        if let values = userDefault.value(forKey: "SavedConversion") as? [String] {
        historyVC.volumeDataOne = values //volumeDataOne now needs to be an [String]
        }
    }

Then on V2, go through your array and labels.