Sigbart error during prepare for segue/unwind segue - swift

Question

I have an app where it is a marketplace and when you click on a product, it opens a detail view controller passing the data to display on the DetailVC. Additionally, inside the DetailVC, if you click on a button to claim the product, it segues to another VC to finalize the transaction.
In the DetailVC, there is a back button which is an unwind segue back to the main marketplace VC. Inside the TransactionVC, there is a cancel button which takes you back to the DetailVC.
When I am clicking the backButton in the DetailVC to take me back to the main market VC but I am getting a SIGBART Error and this :
020-07-15 09:05:23.707490-0500 evolutionatx[707:141952] Could not cast value of type 'evolutionatx.MarketplaceViewController' (0x1032c7868) to 'evolutionatx.PopUpPurchaseViewController' (0x1032c7ba8).
Here is the code for the DetailVC
import UIKit
import iCarousel
import CoreData
class MarketDetailViewController: UIViewController, UIScrollViewDelegate, iCarouselDelegate, iCarouselDataSource {
var productImageArray = [UIImage]()
var productVideo = String()
var pointsToPurchase = String()
var productName = String()
var productDescription = String()
var companyLogo = UIImage()
var companyWebsite = String()
var additionalProductImage = [UIImage]()
var companyName = String()
var promoCODE = String()
var buyLink = String()
var slides:[Slide] = [];
//IB
#IBOutlet weak var productNameLabel: UILabel!
#IBOutlet weak var productPriceLabel: UILabel!
#IBOutlet weak var productDescLabel: UILabel!
#IBOutlet weak var claimButton: UIButton!
#IBOutlet weak var imgScrollView: UIScrollView!
#IBOutlet weak var websiteButton: UIButton!
#IBOutlet weak var pageControl: UIPageControl!
#IBOutlet weak var logoDisplay: UIImageView!
#IBOutlet weak var carouselView: iCarousel!
#IBOutlet weak var otherProductslabe: UILabel!
var carouselImages = [UIImage]()
var evoCoin = Int()
override func awakeFromNib() {
super.awakeFromNib()
carouselImages = productImageArray
}
override func viewDidLoad() {
super.viewDidLoad()
valueSetter()
imgScrollView.delegate = self
slides = createSlides()
setupSlideScrollView(slides: slides)
pageControl.numberOfPages = slides.count
pageControl.currentPage = 0
view.bringSubviewToFront(pageControl)
}
}
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let pageIndex = round(scrollView.contentOffset.x/view.frame.width)
pageControl.currentPage = Int(pageIndex)
let maximumHorizontalOffset: CGFloat = scrollView.contentSize.width - scrollView.frame.width
let currentHorizontalOffset: CGFloat = scrollView.contentOffset.x
// vertical
let maximumVerticalOffset: CGFloat = scrollView.contentSize.height - scrollView.frame.height
let currentVerticalOffset: CGFloat = scrollView.contentOffset.y
let percentageHorizontalOffset: CGFloat = currentHorizontalOffset / maximumHorizontalOffset
let percentageVerticalOffset: CGFloat = currentVerticalOffset / maximumVerticalOffset
}
#IBAction func claimProduct(_ sender: Any) {
print("tap rec")
claimProductandPurchase()
}
func claimProductandPurchase(){
evoCOiner()
if(evoCoin >= Int(pointsToPurchase)!){
print("Transaction Successful")
performSegue(withIdentifier: "proceedQuestion", sender: self)
}
else{
showToast(controller: self, message: "Insufficient EvoCoins", seconds: 0.5)
}
}
func showToast(controller: UIViewController, message : String, seconds: Double) {
let alert = UIAlertController(title: nil, message: message, preferredStyle: .alert)
alert.view.backgroundColor = UIColor.black
alert.view.alpha = 0.6
alert.view.layer.cornerRadius = 15
controller.present(alert, animated: true)
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + seconds) {
alert.dismiss(animated: true)
}
}
func evoCoiner(){
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "EvoCoins")
request.returnsObjectsAsFaults = false
do{
let result = try context.fetch(request)
for data in result as! [NSManagedObject]
{
evoCoin = data.value(forKey: "evoCoins") as! Int
}
}catch{
print("Failed")
}
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let detailController = segue.destination as! PopUpPurchaseViewController
detailController.ppromo = promoCODE
detailController.link = buyLink
detailController.coinToPurchase = Int(pointsToPurchase)!
}
//This is the unwind used by the transaction back button
#IBAction func unwindToItem(segue: UIStoryboardSegue) {
}
}
Here is the code in the transaction VC
import UIKit
import AMTabView
import CoreData
class MarketplaceViewController: UIViewController, TabItem {
#IBOutlet weak var sView: UIView!
#IBOutlet weak var evoCoinLabe: UILabel!
//For the sake of simplicity I only kept the Unwind functions
//MARK: - UNWIND FUNCTIONS
#IBAction func unwindToMainMarketView(segue: UIStoryboardSegue) {
}
}
How can I fix this error?
Please advise if my question was not clear or properly phrased (if so, sorry I am pretty new to all of this)

Answer 1

As #matt already said in his comment and the error clearly states, you cannot cast a MarketplaceViewController to a PopUpPurchaseViewController.
Furthermore instead of doing a forced cast, always look for a safe one like below. Doing so will prevent crashes.
if let detailController = segue.destination as? PopUpPurchaseViewController {
...
}
else {
// log failed to cast
}