ios - 滑动 PageViewController 时如何在 ViewController 中更新 UIPageControl

Question

我有三个类OnboardingViewController , OnboardingPageViewController , 和 OnboardingContentViewController .
在我的 ViewController 类中，我有一个 UIPageControl每当我按下 UIButton 时都会更新在它下面的“下一个”。这是按预期工作的。但是我想制作 UIPageControl根据我在 UIPageViewController 上向左/向右滑动时更新，但我不知道该怎么做。

class OnboardingViewController: UIViewController {

    @IBOutlet weak var nextButton: UIButton!
    @IBOutlet weak var pageControl: UIPageControl!
    
    var onboardingPageViewController: OnboardingPageViewController?
    
    @IBAction func nextButtonTapped(_ sender: UIButton) {
        if let index = onboardingPageViewController?.currentPageIndex {
            switch index {
            case 0:
                onboardingPageViewController?.nextPage()
            case 1:
                onboardingPageViewController?.nextPage()
                nextButton.setTitle("Get Started", for: .normal)
            case 2:
                //present login ViewController after final next button is tapped
            default:
                break
            }
            pageControl.currentPage = index + 1
        }
    }
    
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        let destination = segue.destination
        if let pageViewController = destination as? OnboardingPageViewController {
            onboardingPageViewController = pageViewController
        }
    }
}

class OnboardingContentViewController: UIViewController {
    @IBOutlet var imageView: UIImageView!
    @IBOutlet var titleLabel: UILabel! 
    @IBOutlet var introLabel: UILabel!

    var index = 0
    var contentTitle = ""
    var intro = ""
    var imageFile = ""
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        titleLabel.text = contentTitle
        introLabel.text = intro
        imageView.image = UIImage(named: imageFile)
    }
}

class OnboardingPageViewController: UIPageViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {
    
    var pageTitle = ["Title1", "Title2", "Title3"]
    var pageIntro = ["Description1","Description2","Description3"]
    var pageImages = ["image1","image2","image3"]
    var currentPageIndex = 0
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        dataSource = self
        delegate = self
        
        if let startingViewController = contentViewController(at: currentPageIndex) {
            setViewControllers([startingViewController], direction: .forward,animated: true, completion: nil)
        }
    }
    
    func nextPage() {
        currentPageIndex += 1
        if let nextViewController = contentViewController(at: currentPageIndex){
            setViewControllers([nextViewController], direction:.forward, animated: true, completion:nil)
        }
    }
   
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        var index = (viewController as! OnboardingContentViewController).index
        index -= 1
        return contentViewController(at:index)
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        var index = (viewController as! OnboardingContentViewController).index
        index += 1
        return contentViewController(at:index)
    }
    
    func contentViewController(at index: Int) -> OnboardingContentViewController? {
        if index < 0 || index >= pageIntro.count {
            return nil
        }
        
        let storyboard = UIStoryboard(name: "Onboarding", bundle: nil)
        if let pageContentViewController = storyboard.instantiateViewController(withIdentifier:"OnboardingContentViewController") as? OnboardingContentViewController {
                pageContentViewController.imageFile = pageImages[index]
                pageContentViewController.contentTitle = pageTitle[index]
                pageContentViewController.intro = pageIntro[index]
                pageContentViewController.index = index
                return pageContentViewController
        }
            return nil
    }

}

我尝试将 UIPageViewController 委托(delegate)方法添加到第一个 View Controller ，但我发现控制台中没有打印任何内容。我错过了什么？

class OnboardingViewController: UIViewController, UIPageViewControllerDelegate {

    @IBOutlet weak var pageControl: UIPageControl!

 override func viewDidLoad() {
        super.viewDidLoad()
        
        let pageController = self.storyboard!.instantiateViewController(withIdentifier: "OnboardingPageViewController") as! UIPageViewController
        pageController.delegate = self
        
    }

 func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        if completed == true {
            print("change page control number")
        }
    }

Answer 1

当你这样做 let pageController = self.storyboard!.instantiateViewController... ，您正在初始化页面 View Controller 的新副本。这与您的用户看到的无关。

/// no!
let pageController = self.storyboard!.instantiateViewController(withIdentifier: "OnboardingPageViewController") as! UIPageViewController
pageController.delegate = self

相反，您需要引用 Storyboard中添加的现有页面 View Controller 。它被自动添加为 OnboardingViewController 的第一个 child , 所以你可以使用 self.children[0] .

class OnboardingViewController: UIViewController, UIPageViewControllerDelegate {
    
    @IBOutlet weak var pageControl: UIPageControl!
    
    /// here!
    var pageController: UIPageViewController {
        return self.children[0] as! UIPageViewController
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()

        pageController.delegate = self
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        if completed == true {
            print("change page control number")
        }
    }
}