UIPageViewController 可以返回错误的索引

Posted 2023-03-13

【中文标题】UIPageViewController 可以返回错误的索引

【英文标题】：UIPageViewController can return the wrong index

【发布时间】：2016-04-25 23:57:10

【问题描述】：

正如标题所述，有一种方法可以返回错误的索引。这会弄乱页面底部的索引表示点。完成此操作的方法是在不从屏幕上松开手指的情况下跳过一页。如果发生这种情况，它会弄乱其余的演示点。

here 是它在运行中的样子。

这是用于 UIPageViewController 的代码。

    import UIKit

class PageViewController: UIPageViewController 

    override func preferredStatusBarStyle() -> UIStatusBarStyle 
        return UIStatusBarStyle.LightContent
    

    private(set) lazy var orderedViewControllers: [UIViewController] = 
        return [self.newColoredViewController("Green"),
            self.newColoredViewController("Red"),
            self.newColoredViewController("Blue")]

    ()

    private func newColoredViewController(color: String) -> UIViewController 
        return UIStoryboard(name: "Main", bundle: nil) .
            instantiateViewControllerWithIdentifier("\(color)ViewController")
    

    override func viewDidLoad() 
        super.viewDidLoad()

        dataSource = self

        if let firstViewController = orderedViewControllers.first 
            setViewControllers([firstViewController],
                direction: .Forward,
                animated: true,
                completion: nil)
        

        // Do any additional setup after loading the view.
    

    override func didReceiveMemoryWarning() 
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    


    /*
    // MARK: - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) 
        // Get the new view controller using segue.destinationViewController.
        // Pass the selected object to the new view controller.
    
    */



//MARK: UIPageViewControllerDataSource

extension PageViewController: UIPageViewControllerDataSource 

    func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController? 
        guard let viewControllerIndex = orderedViewControllers.indexOf(viewController) else 
            return nil
        

        let previousIndex = viewControllerIndex - 1

        guard previousIndex >= 0 else 
            return nil
        

        guard orderedViewControllers.count > previousIndex else 
            return nil
        

        return orderedViewControllers[previousIndex]
    

    func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController? 
        guard let viewControllerIndex = orderedViewControllers.indexOf(viewController) else 
            return nil
        

        let nextIndex = viewControllerIndex + 1

        let orderedViewControllersCount = orderedViewControllers.count

        guard orderedViewControllersCount != nextIndex else 
            return nil
        

        guard orderedViewControllersCount > nextIndex else 
            return nil
        

        return orderedViewControllers[nextIndex]
    

    func presentationCountForPageViewController(pageViewController: UIPageViewController) -> Int 
        return orderedViewControllers.count
    

    func presentationIndexForPageViewController(pageViewController: UIPageViewController) -> Int 
        guard let firstViewController = viewControllers?.first,
            firstViewControllerIndex = orderedViewControllers.indexOf(firstViewController) else 
                return 0
        

        return firstViewControllerIndex
    

对此的任何帮助将不胜感激，谢谢。

【问题讨论】：

根据您发布的视频，这听起来像是一个框架错误。我建议登录 Apple 错误报告器并在上面打开一个错误。

@DuncanC 我想是这样，我只是担心这可能只是代码错误。如果不是框架错误，而是我的代码中的缺陷，我不想提交错误报告。

您如何设法用一根手指滑动并跳过页面？除非您的页面没有页面控制器的框架那么宽，否则这可能会使页面控制器感到困惑

@user3802077 我没有只用一根手指滑动。我让 PageController 认为我刷了一个。我小心地滑过一根手指，但没有取下它，然后我将另一根手指放在屏幕上，同时松开第一根手指。现在可以用第二根手指跳过整个页面。

我也将记录一个错误。我可以很容易地重现这个问题。

【参考方案1】：

我做了一个解决方法，因为这仍然没有解决！！已经4年多了。

类到子类而不是UIPageViewController：

import UIKit

class PageController: UIPageViewController 
    lazy var pages: [UIViewController] = []

    var newOffset: CGFloat = 20

    var showReal = true
    var pageControlX: CGFloat = 0 // 0 is the middle of the screen
    var pageControlY: CGFloat = 200

    private var scrollView: UIScrollView?
    private var scrollPoints: [UIView] = []
    private var oldScrollPoints: [UIView] = []

    private var indexKeeper = IndexKeeper()

    private var selectedColor = UIColor(white: 1, alpha: 1)
    private var unselectedColor = UIColor(white: 1, alpha: 0.2)

    override func viewDidLayoutSubviews() 
        super.viewDidLayoutSubviews()

        // whole screen scroll
        scrollView = view.subviews.filter $0 is UIScrollView .first! as? UIScrollView
        scrollView!.frame = UIScreen.main.bounds

        // get pageControl and scroll view from view's subviews
        let pageControl = view.subviews.filter $0 is UIPageControl .first! as! UIPageControl
        oldScrollPoints = pageControl.subviews

        // remove all constraint from view that are tied to pageControl
        let const = view.constraints.filter  $0.firstItem as? NSObject == pageControl || $0.secondItem as? NSObject == pageControl 
        view.removeConstraints(const)

        // customize pageControl
        pageControl.translatesAutoresizingMaskIntoConstraints = false
        pageControl.frame = CGRect(x: pageControlX, y: pageControlY,
                                   width: view.frame.width, height: 0)

        DispatchQueue.main.asyncAfter(deadline: .now() + 0.01) 
            self.replacePoints()
            self.updateIndex()
        
    

    private func replacePoints() 
        for point in scrollPoints 
            point.removeFromSuperview()
        
        scrollPoints = []
        for oldPoint in oldScrollPoints 
            let newPoint = UIView(frame: oldPoint.frame)
            // make rounded
            newPoint.layer.borderWidth = 0
            newPoint.layer.masksToBounds = false
            newPoint.layer.cornerRadius = newPoint.frame.height / 2
            newPoint.clipsToBounds = true

            newPoint.center = CGPoint(x: oldPoint.center.x, y: newOffset)
            newPoint.backgroundColor = oldPoint.backgroundColor
            oldPoint.superview?.addSubview(newPoint)
            scrollPoints.append(newPoint)
            oldPoint.alpha = showReal ? 1 : 0
        
    

    private func offsetFromFirstPage() -> CGFloat 
        var coordinates: [CGFloat] = []
        for (index, page) in pages.enumerated() 
            let offset = scrollView!.convert(scrollView!.bounds.origin, to: page.view!)
            coordinates.append(offset.x + CGFloat(index) * view.frame.width)
        

        let duplicates: [CGFloat] = coordinates.enumerated().map
         current in
            if coordinates.firstIndex(of: current.element) != coordinates.lastIndex(of: current.element) 
                return current.element
             else 
                return .nan
            
        

        return duplicates.first(where:  !$0.isNaN ) ?? 0
    

    private var lastIndex: Int = 0
    private func pageIndexFrom(offset: CGFloat, visibleRatio: CGFloat=0.6) -> Int 
        let adjustedOffset = (offset / view.frame.width)

        if adjustedOffset > CGFloat(lastIndex) + visibleRatio 
            if lastIndex + 1 < pages.count 
                lastIndex += 1
            
         else if adjustedOffset < CGFloat(lastIndex) - visibleRatio 
            if lastIndex - 1 >= 0 
                lastIndex -= 1
            
        
        return lastIndex
    

    private func updateIndex() 
        let fastIndex = pages.firstIndex(of: viewControllers!.first!)!
        indexKeeper.fastIndexUpdate(index: fastIndex)

        let offset = offsetFromFirstPage()
        let slowIndex = pageIndexFrom(offset: offset)
        indexKeeper.slowIndexUpdate(index: slowIndex)

        for (index, point) in scrollPoints.enumerated() 
            if index == indexKeeper.finalIndex 
                point.backgroundColor = selectedColor
             else 
                point.backgroundColor = unselectedColor
            
        

        DispatchQueue.main.asyncAfter(deadline: .now() + 0.01) 
            self.updateIndex()
        
    


class IndexKeeper 
    var finalIndex = 0
    private var slowIndex = 0
    private var fastIndex = 0

    func slowIndexUpdate(index: Int) 
        if index != slowIndex 
            slowIndex = index
            finalIndex = slowIndex
        
    

    func fastIndexUpdate(index: Int) 
        if index != fastIndex 
            fastIndex = index
            finalIndex = fastIndex
        
    

使用示例：

import UIKit

class PageViewController: PageController, UIPageViewControllerDataSource 

    private func pageInstance(name:String) -> UIViewController 
        return UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: name)
    

    override func viewDidLoad() 
        super.viewDidLoad()

        pages = [
            pageInstance(name: "FirstPage"),
            pageInstance(name: "SecondPage"),
            pageInstance(name: "ThirdPage"),
            pageInstance(name: "FourthPage")
        ]

        dataSource = self

        setViewControllers([pages.first!], direction: .forward, animated: false, completion: nil)
    

    // get page before current page
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? 
        guard let index = pages.firstIndex(of: viewController), index > 0 else 
            return nil
        

        return pages[index - 1]
    

    // get page after current page
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? 
        guard let index = pages.firstIndex(of: viewController), index + 1 < pages.count else 
            return nil
        

        return pages[index + 1]
    

    func presentationCount(for pageViewController: UIPageViewController) -> Int 
        return pages.count
    

    func presentationIndex(for pageViewController: UIPageViewController) -> Int 
        if let vc = viewControllers?.first 
            return pages.firstIndex(of: vc)!
        
        return 0
    

【讨论】：

但是***.com/q/12939280/341994 的任何修复都不能修复它吗？

那些是关于以编程方式移动到不同的页面，然后页面的顺序不正确。 ***.com/a/12939384/6304086 在视频中展示了他们正在谈论的内容。

无论如何这些修复都不起作用，因为它们所做的只是以不同的方式以编程方式导航。