如何跳转到 UIPageViewController 中的特定页面，setViewControllers 不起作用

Question

我试图在按下按钮时跳转到特定页面，我制作了一个 ViewController，其中包含 PageViewController 的 ContainerView，这样我就可以在顶部拥有永久按钮。从那里我做：

@IBAction func jump(_ sender: Any) {
    PageViewController().jump()
}

这是PageViewController中的跳转功能

func jump() {

    var lastCoinNumber:Int = Manager.shared.coins.index(of: last!)!
    lastNumber = lastCoinNumber

    if let jumpView = viewControllerAtIndex(lastNumber, storyboard: self.storyboard!) {
        self.setViewControllers([jumpView], direction: .forward, animated: false, completion: nil)
    }
}

由于某种原因，我总是在跳转函数的 ViewControllerAtIndex 部分出错：

线程 1：致命错误：在展开可选值时意外发现 nil .即使我手动选择一个索引，它也会这样做。

if let firstViewController = viewControllerAtIndex(0, storyboard: self.storyboard!) {    
    self.setViewControllers([firstViewController], direction: .forward, animated: false, completion: nil)
}

以上是我在viewDidLoad() 中初始设置 ViewControllers 的方式，效果很好，如果我基本上在做同样的事情，为什么它不起作用？这是我索引页面和实例化视图控制器的方法，它们使用相同的单个视图控制器，因此为每个页面创建它的新实例，否则我会创建一个视图控制器数组。

func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) { if !completed { return }
    DispatchQueue.main.async() {
        self.dataSource = nil
        self.dataSource = self
        self.pageControl.numberOfPages = (Manager.shared.coins.count)
    }
}

func viewControllerAtIndex(_ index: Int, storyboard: UIStoryboard) -> TemplateViewController? {

    if Manager.shared.coins.count == 0 || index >= Manager.shared.coins.count {
        return nil
    }

    let templateViewController = storyboard.instantiateViewController(withIdentifier: "templateController") as! TemplateViewController

    templateViewController.dataObject = Manager.shared.coins[index]
    return templateViewController
}

func indexOfViewController(_ viewController: TemplateViewController) -> Int {
    self.pageControl.currentPage = Manager.shared.coins.index(of: viewController.dataObject)!
    return Manager.shared.coins.index(of: viewController.dataObject)!
}

func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

    var index = self.indexOfViewController(viewController as! TemplateViewController)
    if (index == 0) {
        return nil
    }
    index -= 1
    return self.viewControllerAtIndex(index, storyboard: viewController.storyboard!)
}

func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {

    var index = self.indexOfViewController(viewController as! TemplateViewController)
    if index == -1 {
        return nil
    }
    index += 1
    if index == Manager.shared.coins.count {
        return nil
    }
    return self.viewControllerAtIndex(index, storyboard: viewController.storyboard!)
}

我希望这是足够的信息，谢谢。

编辑：

Coin 是一个字符串数组，我声明：

var last = Manager.shared.coins.last
var lastNumber: Int = 0

然后 jump() 负责其余的工作。所以我得到最后一个对象，找到它的索引，然后用最后一个数字的索引执行 setViewControllers，它应该与 viewControllerAtIndex 对应，因为它使用相同的数组来索引和加载页面。

出于某种原因，当我尝试这样做时： var lastCoinNumber:Int = Manager.shared.coins.index(of: last) 它迫使我使用！因为： “可选类型'Array.Index的值？' （又名“可选”）未展开；您的意思是使用“！”还是‘？’？”

我不确定我在这方面做错了什么，这是硬币的声明方式：

var coins = [""]

编辑：完整代码，PageViewController：

import UIKit

var pageView = PageViewController()

class PageViewController: UIPageViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {

    //page Control dots
    var pageControl = UIPageControl()
    var last = Manager.shared.coins.last!
    var lastNumber: Int = 0


    var viewControllerArray = [UIViewController()]


    func configurePageControl() {
    // The total number of pages that are available is based on ManagerCoins names array
        pageControl = UIPageControl(frame: CGRect(x: 0,y: 
    UIScreen.main.bounds.maxY - 50,width: UIScreen.main.bounds.width,height: 
    50))
        self.pageControl.numberOfPages = (Manager.shared.coins.count)
        self.pageControl.currentPage = 0
        self.pageControl.tintColor = UIColor.black
        self.pageControl.pageIndicatorTintColor = UIColor.gray
        self.pageControl.currentPageIndicatorTintColor = UIColor.white
        self.view.addSubview(pageControl)
    }

    // MARK: Delegate functions
    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {

    }

    func viewControllerAtIndex(_ index: Int, storyboard: UIStoryboard) -> TemplateViewController? {

        if Manager.shared.coins.count == 0 || index >= Manager.shared.coins.count {
            return nil
        }

        let templateViewController = storyboard.instantiateViewController(withIdentifier: "templateController") as! TemplateViewController

        templateViewController.dataObject = Manager.shared.coins[index]
        return templateViewController
    }

    func indexOfViewController(_ viewController: TemplateViewController) -> Int {
        self.pageControl.currentPage = Manager.shared.coins.index(of: viewController.dataObject)!
        return Manager.shared.coins.index(of: viewController.dataObject)!
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

        var index = self.indexOfViewController(viewController as! TemplateViewController)
        if (index == 0) {
            return nil
        }
        index -= 1
        return self.viewControllerAtIndex(index, storyboard: viewController.storyboard!)
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {

        var index = self.indexOfViewController(viewController as! TemplateViewController)
        if index == -1 {
            return nil
        }
        index += 1
        if index == Manager.shared.coins.count {
            return nil
        }
        return self.viewControllerAtIndex(index, storyboard: viewController.storyboard!)
    }

    func jump() {

        var lastCoinNumber:Int = Manager.shared.coins.index(of: last!)!
        lastNumber = lastCoinNumber

        if let jumpView = viewControllerAtIndex(lastCoinNumber, storyboard: self.storyboard!){
            self.setViewControllers([jumpView], direction: .forward, animated: false, completion: nil)
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        self.delegate = self
        configurePageControl()

        self.dataSource = self

        if let firstViewController = viewControllerAtIndex(0, storyboard: self.storyboard!){

            self.setViewControllers([firstViewController], direction: .forward, animated: false, completion: nil)
        }
    }
}

编辑：

经过大量研究，这似乎是跳转页面的正确方法，通过调用 setViewControllers，对此答案的第一条评论似乎有同样的问题，它适用于在 viewDidLoad() 上设置视图但试图以编程方式导航到基于索引的页面出现错误。 https://*.com/a/24335008/10058239

Answer 1

我认为它因为强制展开而崩溃：

var lastCoinNumber:Int = Manager.shared.coins.index(of: last!)!

如果硬币是一个集合，您可以使用 .last 来获取最后一个元素，例如：

let numbers = [10, 20, 30, 40, 50]
if let lastNumber = numbers.last {
    print(lastNumber)
}
// Prints "50"