Swift：无法使用发件人通过segue设置[String]

Question

Good day. I'm creating my first own app and have ran into an issue. I have a AR scene with clickable stuff which when you touch them a segue triggers into a ViewController and sets that view controllers labels and textview depending on what was touch on screen.

Explanations: 1. CaseViewController is the target view controller. 2. the "artNews" and "politicalNews" are string arrays in which I've written 3 strings, they are defined and are never nil.

Question: I get a crash due to the segueInputText being nil. Why does it become nil and how do I correct it?

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

    let destinationVC = segue.destination as! CaseViewController
    destinationVC.segueInputText = sender as? [String]

    print("\(String(describing: sender))")
}

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {

    guard let touchLocation = touches.first?.location(in: sceneView),
        let hitNode = sceneView?.hitTest(touchLocation, options: nil).first?.node,
        let nodeName = hitNode.name
        else { return }

    if nodeName == imageNameArray[0] {

        performSegue(withIdentifier: "CaseViewController", sender: artNews)

    } else {
        print("Found no node connected to \(nodeName)")
        return
    }

    if nodeName == imageNameArray[1] {

        performSegue(withIdentifier: "CaseViewController", sender: politicalNews)

    } else {
        print("Found no node connected to \(nodeName)")
        return
    }

the CaseViewController has UILabels and UITextViews connected and this:

    var segueInputText : [String]? {
    didSet {
        setupText()
    }
}

    func setupText() {

    // Why are these values nil? 
    testLabel.text = segueInputText![0]
    ingressLabel.text = segueInputText![1]
    breadLabel.text = segueInputText![2]

    testLabel.reloadInputViews()
    ingressLabel.reloadInputViews()
    breadLabel.reloadInputViews() //breadLabel is a UITextView
}

Thank you for reading my question! Kind regards.

Answer 1

Remove didSet block as when you set the array inside prepare , observe triggers and the lbl is still nil

OR

func setupText() {
   if testLabel == nil { // if one is nil then all of them too
     return 
   }
 }

Answer 2

Don't use the didSet observer in this case. It will never work.

In setupText() IBOutlets are accessed which are not connected yet at the moment prepare(for is called.

---

Remove the observer

var segueInputText : [String]?

and call setupText in viewWillAppear

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    setupText()
}

Answer 3

At the very moment when you do this:

destinationVC.segueInputText = sender as? [String]

the destination view controller has not yet loaded hence none of the outlets are connected so accessing any of them will crash your app as they are still nil.

You will have to assign any of the values you'd like to pass to the destination controller to a property and assign this property's value to the the corresponding outlet in viewDidLoad . This way you make sure all outlets have connected.

For the same reason don't use a property observer to assign the property's value to any of the labels as this would happen, again, before the view controller had a chance to load…