iOS/Xcode：Koloda 框架：在隐式展开 Optional 值时意外发现 nil答案

【问题标题】：iOS/Xcode: Koloda framework: Unexpectedly found nil while implicitly unwrapping an Optional valueiOS/Xcode：Koloda 框架：在隐式展开 Optional 值时意外发现 nil
【发布时间】：2020-06-29 20:30:49
【问题描述】：

我正在尝试将这个 Koloda 框架实现到我的应用程序中。 (https://github.com/Yalantis/Koloda)。但是，当我运行我的应用程序时，我在 kolodaView.delegate = self 行中收到一个错误，上面写着“Unexpectedly found nil while implicitly unwrapping an Optional value”

我已经尝试调试代码几个小时，但无法理解 nil 值的来源。下面是我的视图控制器文件：

import UIKit
import Koloda
import pop

private let numberOfCards: Int = 5
private let frameAnimationSpringBounciness: CGFloat = 9
private let frameAnimationSpringSpeed: CGFloat = 16
private let kolodaCountOfVisibleCards = 2
private let kolodaAlphaValueSemiTransparent: CGFloat = 0.1

class CardViewController: UIViewController {
    
    @IBOutlet weak var kolodaView: CardView!
    //MARK: Lifecycle
    
    fileprivate var dataSource: [UIImage] = {
        var array: [UIImage] = []
        for index in 0..<numberOfCards {
            array.append(UIImage(named: "cards_\(index + 1)")!)
        }
        return array
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
//        kolodaView.alphaValueSemiTransparent = kolodaAlphaValueSemiTransparent
//        kolodaView.countOfVisibleCards = kolodaCountOfVisibleCards
        kolodaView.delegate = self
        kolodaView.dataSource = self
//        kolodaView.animator = BackgroundKolodaAnimator(koloda: kolodaView)
//        self.modalTransitionStyle = UIModalTransitionStyle.flipHorizontal
    }
    
    
//    //MARK: IBActions
//    @IBAction func leftButtonTapped() {
//        kolodaView?.swipe(.left)
//    }
//
//    @IBAction func rightButtonTapped() {
//        kolodaView?.swipe(.right)
//    }
//
//    @IBAction func undoButtonTapped() {
//        kolodaView?.revertAction()
//    }
}

//MARK: KolodaViewDelegate
extension CardViewController: KolodaViewDelegate {
    
    func kolodaDidRunOutOfCards(_ koloda: KolodaView) {
        kolodaView.resetCurrentCardIndex()
        kolodaView.reloadData()
    }
    
    func koloda(_ koloda: KolodaView, didSelectCardAt index: Int) {
        let myUrl = "https://yalantis.com/"
        if let url = URL(string: "\(myUrl)"), !url.absoluteString.isEmpty {
            UIApplication.shared.open(url, options: [:], completionHandler: nil)
        }
    }
    
    func kolodaShouldApplyAppearAnimation(_ koloda: KolodaView) -> Bool {
        return true
    }

    func kolodaShouldMoveBackgroundCard(_ koloda: KolodaView) -> Bool {
        return false
    }

    func kolodaShouldTransparentizeNextCard(_ koloda: KolodaView) -> Bool {
        return true
    }

    func koloda(kolodaBackgroundCardAnimation koloda: KolodaView) -> POPPropertyAnimation? {
        let animation = POPSpringAnimation(propertyNamed: kPOPViewFrame)
        animation?.springBounciness = frameAnimationSpringBounciness
        animation?.springSpeed = frameAnimationSpringSpeed
        return animation
    }
}

// MARK: KolodaViewDataSource
extension CardViewController: KolodaViewDataSource {
    
    func kolodaSpeedThatCardShouldDrag(_ koloda: KolodaView) -> DragSpeed {
        return .default
    }
    
    func kolodaNumberOfCards(_ koloda: KolodaView) -> Int {
        return numberOfCards
    }
    
    func koloda(_ koloda: KolodaView, viewForCardAt index: Int) -> UIView {
        return UIImageView(image: UIImage(named: "cards_\(index + 1)"))
    }
    
//    func koloda(_ koloda: KolodaView, viewForCardOverlayAt index: Int) -> OverlayView? {
//        return Bundle.main.loadNibNamed("CustomOverlayView", owner: self, options: nil)?[0] as? OverlayView
//    }
 }

如果有人能指出 self.delegate 如何返回 nil，将不胜感激。

【问题讨论】：

您是否确保“卡片视图”指向故事板中的正确委托？
是的，卡片视图是一个返回 CGrect 并在情节提要中创建 UIView 的类。我在 Assets 文件夹中有图片“card_1, card_2, ..”，理想情况下 main.storyboard 中的 UIView 应该显示这些卡片并允许用户在它们上向左或向右滑动。

标签： ios swift xcode koloda

【解决方案1】：

错误清楚地表明某些东西是 nil 并且您不能在这一行中强制展开：

kolodaView.delegate = self

这里，显然只有kolodaView 可以产生崩溃。这意味着在以下行中与情节提要的连接丢失了。在以下行中重新连接到情节提要中的kolodaView。

@IBOutlet weak var kolodaView: CardView!

【讨论】：