如何确保在加载之前我没有访问插座

Question

我正在制作一个交互式故事应用程序。 PageController: UIViewController 控制故事，第一页加载正常，但是当我进行选择时，应用程序崩溃并出现致命错误 Unexpected found nil when unwrapping。上线：

firstChoiceButton.setTitle(firstChoice.title, for: UIControlState())

查了一下，好像有一个可选的...也许它没有与我的 Story.swift 文件通信？

也许是@IBOutlet firstChoiceButton？但是我认为我所有的@IBOutlets/Actions 都正确连接了...帮助？

import UIKit
class PageController: UIViewController {

    @IBOutlet weak var storyLabel: UILabel!
    @IBOutlet weak var firstChoiceButton: UIButton!
    @IBOutlet weak var secondChoiceButton: UIButton!
    @IBOutlet weak var backdrop2: UIImageView!

    var page: Page?

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)}

    init(page: Page) {
        self.page = page
        super.init(nibName: nil, bundle: nil)}

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()}
    override func viewDidLoad() {
        super.viewDidLoad()


    if let page = page {

            let attributedString = NSMutableAttributedString(string:    page.story.text)

            let paragraphStyle = NSMutableParagraphStyle()

            paragraphStyle.lineSpacing = 5

            attributedString.addAttribute(NSParagraphStyleAttributeName, value: paragraphStyle, range: NSMakeRange(0, attributedString.length))

    if let firstChoice = page.firstChoice {

        firstChoiceButton.setTitle(firstChoice.title, for: UIControlState())

            firstChoiceButton.addTarget(self, action: #selector(PageController.loadFirstChoice), for: .touchUpInside)

            } else {

                firstChoiceButton.setTitle("Meep", for: UIControlState())
                firstChoiceButton.addTarget(self, action: #selector(PageController.playAgain), for: .touchUpInside)
            }

            if let secondChoice = page.secondChoice {

                secondChoiceButton.setTitle(secondChoice.title, for: UIControlState())

               secondChoiceButton.addTarget(self, action: #selector(PageController.loadSecondChoice), for: .touchUpInside)
            }
        storyLabel.attributedText = attributedString
    }
    }

    @IBAction func loadFirstChoice() {
        if let page = page, let firstChoice = page.firstChoice {
            let nextPage = firstChoice.page
            let pageController = PageController(page: nextPage)

            //    playSound(nextPage.story.soundEffectURL as URL)
            navigationController?.pushViewController(pageController, animated: true)
        }
    }

    @IBAction func loadSecondChoice() {
        if let page = page, let secondChoice = page.secondChoice {
            let nextPage = secondChoice.page
            let pageController = PageController(page: nextPage)

          //  playSound(nextPage.story.soundEffectURL as URL)
            navigationController?.pushViewController(pageController, animated: true)
        }
    }

    @IBAction func playAgain() {
        navigationController?.popToRootViewController(animated: true)
    }
}

Answer 1

您应该以编程方式实例化视图控制器并将其推送到导航控制器堆栈。这里有一些代码可以帮助您入门。

func loadFirstChoice() {
        if let page = page, let firstChoice = page.firstChoice {
            let nextPage = firstChoice.page
            //let pageController = PageController(page: nextPage)

            //    playSound(nextPage.story.soundEffectURL as URL)
            let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)

            if let newPage = mainStoryboard.instantiateViewController(withIdentifier: "newpage") as? PageController { //newpage is the storyboard id of the view controller
                newPage.page = nextPage
                navigationController?.pushViewController(newPage, animated: true)
            }
        }
    }