准备 segue/unwind segue 期间出现 Sigbart 错误

Question

我有一个应用程序，它是一个市场，当您单击产品时，它会打开一个详细视图控制器，传递数据以显示在详细信息VC 上。此外，在详细信息VC 中，如果您单击一个按钮来领取产品，它会转到另一个 VC 以完成交易。

在详细信息VC 中，有一个后退按钮，可以返回到主要市场 VC。在 TransactionVC 中，有一个取消按钮，可以将您带回到 DetailVC。

当我单击详细信息中的后退按钮时VC 将我带回主要市场 VC 但我收到 SIGBART 错误，并且：
020-07-15 09:05:23.707490-0500 evolutionatx[707:141952] Could not cast value of type 'evolutionatx.MarketplaceViewController' (0x1032c7868) to 'evolutionatx.PopUpPurchaseViewController' (0x1032c7ba8).

这是详细信息的代码VC

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) {
}
}

这是交易中的代码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) {
   }
   }

我该如何解决这个错误？

如果我的问题不清楚或措辞不当，请告知（如果是，对不起，我对这一切都很陌生）

Answer 1

正如@matt 在他的评论中已经说过的那样，错误也清楚地指出，你不能将 MarketplaceViewController 转换为 PopUpPurchaseViewController。

此外，不要强制转换，而是始终寻找如下所示的安全转换。这样做可以防止崩溃。

if let detailController = segue.destination as? PopUpPurchaseViewController {
    ...
}
else { 
    // log failed to cast
}

准备 segue/unwind segue 期间出现 Sigbart 错误

Sigbart error during prepare for segue/unwind segue

swift

xcode

storyboard

uistoryboardsegue

unwind-segue