Swift 3 - Prepare Segue

Question

I have 3 scenes in my storyboard. My initial View Controller is a Navigation Controller, then there is a relationship root view controller to a UI ViewController (view contr

Answer 1

I had the same issue. The logic is that one first prepares the segue (loads the UIViewController referenced by the container view), assigns it to a variable, and then uses it in viewDidLoad(). This code should work:

Swift 4.2

// usually an IBoutlet
var viewController: HistoryController!

override func viewDidLoad() {
    super.viewDidLoad()

    viewController.detailItem = barcodeInt as AnyObject
}

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "HistorySegue"
    { viewController = segue.destination as! HistoryController }
}

detailItem could possibly be defined as an IBoutlet in HistoryController, it depends on the OP code. In my case, where I had two simple container views with a label each inside, this has been the final working code for the main view controller class:

import UIKit

class ViewController: UIViewController {

    @IBOutlet var firstView: ReusableViewController!
    @IBOutlet var secondView: ReusableViewController!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        firstView.myLabel.text = "My 1st reuse!!!"
        secondView.myLabel.text = "And that's the 2nd!"
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if (segue.identifier == "segueFirstView")
        { firstView = (segue.destination as! ReusableViewController) }
        if (segue.identifier == "segueSecondView")
        { secondView = (segue.destination as! ReusableViewController) }
    }
}

With that I could finally change the text of the two different UILabel directly from the main controller!

For a detailed explanation of how to use the container views one may check this S.O. answer.