如何修复 UIPageViewController 手动分页？

编程问答 2022-05-22

问题描述

UIPageViewController 手动分页无法正常工作。

自动分页工作正常，但当我们手动旋转时，它无法正常工作。

我的ViewController.Swift代码

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var contentView: UIView!
    @IBOutlet weak var pageControl: UIPageControl!
    let myDataSource = ["Img1","Img2","Img3","Img4"]
    let urlDataSource = ["https://fabric.io/","https://about.gitlab.com/","https://developer.apple.com/","https://fast.com/"]
    var currentVCIndex = 0
    var timer = Timer()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        configurePageViewController()
        timerStart()
    }

    func timerStart() {
        timer.invalidate()
        timer = Timer.scheduledTimer(timeInterval: 5.0,target: self,selector: #selector(configurePageViewController),userInfo: nil,repeats: true)
    }
    
    @objc func configurePageViewController() {
        guard let pageVc = storyboard?.instantiateViewController(identifier: "CustomPageViewController") as? CustomPageViewController else {
            return
        }
        
        pageVc.delegate = self
        pageVc.dataSource = self
        
        addChild(pageVc)
        pageVc.didMove(toParent: self)
        
        pageVc.view.translatesAutoresizingMaskIntoConstraints = false
                        
        pageControl.layer.zPosition = 1;
        pageControl.numberOfPages = myDataSource.count
        pageControl.currentPageIndicatorTintColor = .lightGray
        pageControl.pageIndicatorTintColor = .white
        
        contentView.addSubview(pageVc.view)
        
        let views : [String : Any] = ["pageView": pageVc.view!]
        
        contentView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|-0-[pageView]-0-|",options: NSLayoutConstraint.FormatOptions(rawValue: 0),metrics: nil,views: views))
        
        contentView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|-0-[pageView]-0-|",views: views))
        guard let startingVc = detailVCAt(index: currentVCIndex) else {
            return
        }
        
        pageVc.setViewControllers([startingVc],direction: .forward,animated: true)

        increaseCount()
    }
    
    func increaseCount() {
        pageControl.currentPage = currentVCIndex
        
        if currentVCIndex == 3 {
            currentVCIndex = 0
        } else {
            currentVCIndex = currentVCIndex+1
        }
    }
    
    func detailVCAt(index: Int) -> DataViewController? {
        
        if index >= myDataSource.count || myDataSource.count == 0 {
            return nil
        }
        
        guard let dataVC = storyboard?.instantiateViewController(identifier: "DataViewController") as? DataViewController else {
            return nil
        }
        
        dataVC.index = index
        dataVC.displayImgName = myDataSource[index]
        dataVC.redirectURL = urlDataSource[index]
        
        return dataVC
    }

}

extension ViewController: UIPageViewControllerDelegate,UIPageViewControllerDataSource {
    
    func presentationIndex(for _: UIPageViewController) -> Int {
        return myDataSource.count
    }
    
    func presentationCount(for _: UIPageViewController) -> Int {
        return myDataSource.count
    }
    
    func pageViewController(_: UIPageViewController,viewControllerBefore viewController: UIViewController) -> UIViewController? {
        
        let dataVc = viewController as? DataViewController
        
        guard var currentIndex = dataVc?.index else {
            return nil
        }

        currentVCIndex = currentIndex
        
        if currentIndex == 0 {
            return nil
        }

        currentIndex -= 1
        pageControl.currentPage = currentVCIndex
    //        timerStart()
    //        increaseCount()
        return detailVCAt(index: currentIndex)
    }
    
    func pageViewController(_: UIPageViewController,viewControllerAfter viewController: UIViewController) -> UIViewController? {
        
        let dataVc = viewController as? DataViewController
        
        guard var currentIndex = dataVc?.index else {
            return nil
        }

        if currentIndex == myDataSource.count {
            return nil
        }
        
        currentIndex += 1

        currentVCIndex = currentIndex
        pageControl.currentPage = currentVCIndex
    //        timerStart()
    //        increaseCount()
        return detailVCAt(index: currentIndex)
    }
    
    
}

我的DataViewController.Swift代码

import UIKit

class DataViewController: UIViewController {
    
    @IBOutlet weak var btn: UIButton!
    var displayImgName :String?
    var redirectURL :String?
    var index: Int?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        btn.setImage(UIImage.init(named: displayImgName ?? ""),for: .normal)
    }
    
    @IBAction func onClickBtn(_ sender: UIButton) {
        
        if let url = URL(string: redirectURL ?? ""),UIApplication.shared.canOpenURL(url) {
            if #available(iOS 10.0,*) {
                UIApplication.shared.open(url,options: [:],completionHandler: nil)
            } else {
                UIApplication.shared.openURL(url)
            }
        }
    }
    
}

我的CustomPageViewController.Swift代码

import UIKit

class CustomPageViewController: UIPageViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }
       
}

我的故事板图片

enter image description here

解决方法

在您的代码中，currentIndex 出错了。您可以使用以下委托方法来获取正确的 currentIndex。

func pageViewController(_ pageViewController: UIPageViewController,didFinishAnimating finished: Bool,previousViewControllers: [UIViewController],transitionCompleted completed: Bool)

同样在您的预定计时器中，configurePageViewController 方法每 5 秒调用一次。该方法在调用方法时创建了一个新的UIPageViewController实例并添加了一个子视图，这会导致以后出现内存问题。

我建议您是否使用故事板添加嵌入在 ContainerView 中的 UIPageViewController。你可以找到附件截图。

对于您的情况，我有更好的解决方案。请找到以下代码：

我的ViewController.Swift代码：

class ViewController: UIViewController {
    
    @IBOutlet weak var contentView: UIView!
    @IBOutlet weak var pageControl: UIPageControl!
    let myDataSource = ["Img1","Img2","Img3","Img4"]
    let urlDataSource = ["https://fabric.io/","https://about.gitlab.com/","https://developer.apple.com/","https://fast.com/"]
    var timer = Timer()
    var pageViewController: CustomPageViewController? {
        didSet {
            pageViewController?.objViewController = self
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        configurePageControl()
        timerStart()
    }
    
    override func prepare(for segue: UIStoryboardSegue,sender: Any?) {
        if let pageViewController = segue.destination as? CustomPageViewController {
            self.pageViewController = pageViewController
        }
    }
    
    func pageViewIdexChange(_ index : Int) {
        pageControl.currentPage = index
    }
    
    func timerStart() {
        timer.invalidate()
        guard let pageViewController = pageViewController else { return }
        timer = Timer.scheduledTimer(timeInterval: 5.0,target: pageViewController,selector: #selector(pageViewController.scrollToNextViewController),userInfo: nil,repeats: true)
    }

    func configurePageControl() {
        pageControl.numberOfPages = myDataSource.count
        pageControl.currentPageIndicatorTintColor = .lightGray
        pageControl.pageIndicatorTintColor = .white
    }
    
}

我的DataViewController.Swift代码：

class DataViewController: UIViewController {
    
    @IBOutlet weak var btn: UIButton!
    var displayImgName :String?
    var redirectURL :String?
    var index: Int?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        btn.setImage(UIImage.init(named: displayImgName ?? ""),for: .normal)
        view.backgroundColor = .random()
    }
    
    @IBAction func onClickBtn(_ sender: UIButton) {
        
        if let url = URL(string: redirectURL ?? ""),UIApplication.shared.canOpenURL(url) {
            if #available(iOS 10.0,*) {
                UIApplication.shared.open(url,options: [:],completionHandler: nil)
            } else {
                UIApplication.shared.openURL(url)
            }
        }
    }
    
}

我的 CustomPageViewController.Swift 代码：

import UIKit

class CustomPageViewController: UIPageViewController {
    
    weak var objViewController: ViewController?
    var myDataSource: [String] = []
    var urlDataSource: [String] = []
    var currentIndex = 0
    
    private(set) lazy var orderedViewControllers: [UIViewController] = {
        // The view controllers will be shown in this order
        var vcs : [DataViewController] = []
        for i in 0 ..< myDataSource.count {
            vcs.append(detailVCAt(index: i)!)
        }
        return vcs
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        dataSource = self
        delegate = self
        
        myDataSource = objViewController?.myDataSource ?? []
        urlDataSource = objViewController?.urlDataSource ?? []
        
        if let initialViewController = orderedViewControllers.first {
            scrollToViewController(initialViewController)
        }
    }
    
    func detailVCAt(index: Int) -> DataViewController? {
        
        if index >= myDataSource.count || myDataSource.count == 0 {
            return nil
        }
        
        guard let dataVC = storyboard?.instantiateViewController(identifier: "DataViewController") as? DataViewController else {
            return nil
        }
        
        dataVC.index = index
        dataVC.displayImgName = myDataSource[index]
        dataVC.redirectURL = urlDataSource[index]
        
        return dataVC
    }
    
    //MARK: - Methods
    @objc func scrollToNextViewController() {
        if currentIndex < orderedViewControllers.count - 1 {
            scrollToViewController(currentIndex + 1)
        } else {
            scrollToViewController(0,direction: .forward)
        }
    }
    
    func scrollToViewController(_ newIndex: Int,direction: UIPageViewController.NavigationDirection? = nil) {
        var direction = direction
        if let firstViewController = viewControllers?.first,let currentIndex = orderedViewControllers.firstIndex(of: firstViewController) {
            if direction == nil {
                direction = newIndex >= currentIndex ? .forward : .reverse
            }
            let nextViewController = orderedViewControllers[newIndex]
            scrollToViewController(nextViewController,direction: direction!)
        }
    }
    
    func scrollToViewController(_ viewController: UIViewController,direction: UIPageViewController.NavigationDirection = .forward) {
        setViewControllers([viewController],direction: direction,animated: true,completion: { (finished) -> Void in
                            // Setting the view controller programmatically does not fire
                            // any delegate methods,so we have to manually notify the
                            // 'tutorialDelegate' of the new index.
                            self.notifyTutorialDelegateOfNewIndex()
                           })
    }
    
    private func notifyTutorialDelegateOfNewIndex() {
        
        if let firstViewController = viewControllers?.first,let index = orderedViewControllers.firstIndex(of: firstViewController) {
            currentIndex = index
            objViewController?.pageViewIdexChange(index)
        }
    }
    
    
}

// MARK: - UIPageViewControllerDataSource & UIPageViewControllerDelegate
extension CustomPageViewController : UIPageViewControllerDataSource,UIPageViewControllerDelegate {
    func pageViewController(_ pageViewController: UIPageViewController,viewControllerBefore viewController: UIViewController) -> UIViewController? {
        guard let viewControllerIndex = orderedViewControllers.firstIndex(of: viewController) else {
            return nil
        }
        
        let previousIndex = viewControllerIndex - 1
        
        // User is on the first view controller and swiped left to loop to
        // the last view controller.
        guard previousIndex >= 0 else {
            return orderedViewControllers.last
        }
        
        guard orderedViewControllers.count > previousIndex else {
            return nil
        }
        
        return orderedViewControllers[previousIndex]
    }
    
    func pageViewController(_ pageViewController: UIPageViewController,viewControllerAfter viewController: UIViewController) -> UIViewController? {
        guard let viewControllerIndex = orderedViewControllers.firstIndex(of: viewController)  else {
            return nil
        }
        
        let nextIndex = viewControllerIndex + 1
        let orderedViewControllersCount = orderedViewControllers.count
        
        // User is on the last view controller and swiped right to loop to
        // the first view controller.
        guard orderedViewControllersCount != nextIndex else {
            return orderedViewControllers.first
        }
        
        guard orderedViewControllersCount > nextIndex else {
            return nil
        }
        
        return orderedViewControllers[nextIndex]
    }
    func pageViewController(_ pageViewController: UIPageViewController,transitionCompleted completed: Bool) {
        
        notifyTutorialDelegateOfNewIndex()
    }
    
}

我的故事板图片

StoryBoard

,

您代码中的问题是您无法确定当前可见视图控制器的索引，在 pageViewController(_:viewControllerBefore:) 的 pageViewController(_:viewControllerAfter:) 和 UIPageViewControllerDataSource 函数内，因为这些委托每次滚动时，函数可能会被调用多次。

例如，如果您当前位于索引 0 并滚动到索引 1，则 pageViewController(_:viewControllerAfter:) 函数将被调用 2 次，一次用于索引 1，一次用于索引 2 以预加载下一页。

>

话虽如此，您几乎可以在 this 答案之后并使用 pageViewController(_:didFinishAnimating:previousViewControllers:transitionCompleted:) 的 UIPageViewControllerDelegate 函数找到当前可见视图控制器的索引，但只需稍作修改即可满足您的需求：

extension ViewController: UIPageViewControllerDelegate {
    func pageViewController(_ pageViewController: UIPageViewController,transitionCompleted completed: Bool) {
        guard
            completed,let currentIndex = (viewControllers?.first as? DataViewController)?.index
        else {
            return
        }
        currentVCIndex = currentIndex
        pageControl.currentPage = currentVCIndex
    }
}

此外，由于您使用的是自定义 presentationIndex(for:)，因此无需实现 presentationCount(for:) 的 UIPageViewControllerDataSource 和 UIPageControl 函数。因此，您的扩展程序可能如下所示：

extension ViewController: UIPageViewControllerDataSource {
    func pageViewController(_: UIPageViewController,viewControllerBefore viewController: UIViewController) -> UIViewController? {
        
        let dataVc = viewController as? DataViewController
        
        guard var currentIndex = dataVc?.index else {
            return nil
        }
        
        if currentIndex == 0 {
            return nil
        }

        currentIndex -= 1
        
        return detailVCAt(index: currentIndex)
    }

    func pageViewController(_: UIPageViewController,viewControllerAfter viewController: UIViewController) -> UIViewController? {
        
        let dataVc = viewController as? DataViewController
        
        guard var currentIndex = dataVc?.index else {
            return nil
        }

        if currentIndex == myDataSource.count {
            return nil
        }
        
        currentIndex += 1
        
        return detailVCAt(index: currentIndex)
    }
}
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