UIPageViewController-检测滚动到下一个视图控制器几乎可以正常工作中途以更改按钮颜色吗？

如何解决UIPageViewController-检测滚动到下一个视图控制器几乎可以正常工作中途以更改按钮颜色吗？

我有一个类继承了UIPageViewController，该类包含4个控制器，我试图弄清楚如何在滚动到第二个视图控制器时更改按钮的颜色

按钮颜色只能在第一个控制器上改变

此代码几乎可以正常工作，但行为仅对第三个控制器而言并不正确，这意味着解决方案不正确。

如果有人可以帮忙，我将非常感激。谢谢

    public func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let point = scrollView.contentOffset
        let width = scrollView.frame.width
        let percentComplete = abs(point.x - width) / width
        let page = Int(round(percentComplete))

        if percentComplete >= 0.5 {
            if page == 1,currentIndex == 1 {
                nextButton.backgroundColor = .red
            } else {
                nextButton.backgroundColor = .blue
            }
            print ("percentComplete: ",percentComplete,"page: ",page,"currentIndex: ",currentIndex,"point: ",point.x)
        }
    }

解决方法

即使您说要使用UIPageViewController，这也是使用UIScrollView的示例实现，您可能会发现它更易于管理：

class PagedScrollViewController: UIViewController,UIScrollViewDelegate {
    
    let scrollView: UIScrollView = {
        let v = UIScrollView()
        v.isPagingEnabled = true
        v.bounces = false
        return v
    }()
    
    let pageControl: UIPageControl = {
        let v = UIPageControl()
        return v
    }()
    
    let stack: UIStackView = {
        let v = UIStackView()
        v.axis = .horizontal
        v.distribution = .fillEqually
        return v
    }()
    
    var pages: [UIViewController] = []
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        pageControl.translatesAutoresizingMaskIntoConstraints = false
        stack.translatesAutoresizingMaskIntoConstraints = false
        
        scrollView.addSubview(stack)
        view.addSubview(scrollView)
        view.addSubview(pageControl)
        
        let g = view.safeAreaLayoutGuide
        let svCLG = scrollView.contentLayoutGuide
        let svFLG = scrollView.frameLayoutGuide
        
        NSLayoutConstraint.activate([
            
            scrollView.topAnchor.constraint(equalTo: g.topAnchor,constant: 20.0),scrollView.leadingAnchor.constraint(equalTo: g.leadingAnchor,scrollView.trailingAnchor.constraint(equalTo: g.trailingAnchor,constant: -20.0),scrollView.bottomAnchor.constraint(equalTo: g.bottomAnchor,constant: -80.0),stack.topAnchor.constraint(equalTo: svCLG.topAnchor,constant: 0.0),stack.leadingAnchor.constraint(equalTo: svCLG.leadingAnchor,stack.trailingAnchor.constraint(equalTo: svCLG.trailingAnchor,stack.bottomAnchor.constraint(equalTo: svCLG.bottomAnchor,stack.heightAnchor.constraint(equalTo: svFLG.heightAnchor,pageControl.topAnchor.constraint(equalTo: scrollView.bottomAnchor,constant: 8.0),pageControl.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor),pageControl.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor),])
        
        // if we're loading "page" view controllers from Storyboard
        /*
        if let vc = storyboard?.instantiateViewController(withIdentifier: "psFirst") as? PSFirstViewController {
            pages.append(vc)
        }
        if let vc = storyboard?.instantiateViewController(withIdentifier: "psSecond") as? PSSecondViewController {
            pages.append(vc)
        }
        if let vc = storyboard?.instantiateViewController(withIdentifier: "psThird") as? PSThirdViewController {
            pages.append(vc)
        }
        if let vc = storyboard?.instantiateViewController(withIdentifier: "psFourth") as? PSFourthViewController {
            pages.append(vc)
        }
        pages.forEach { vc in
            self.addChild(vc)
            stack.addArrangedSubview(vc.view)
            vc.view.widthAnchor.constraint(equalTo: scrollView.frameLayoutGuide.widthAnchor,constant: 0.0).isActive = true
            vc.didMove(toParent: self)
        }
        */

        // for this example,//  create 4 view controllers,with background colors
        let colors: [UIColor] = [
            .red,.brown,.blue,.magenta
        ]
        colors.forEach { c in
            let vc = BasePageController()
            vc.view.backgroundColor = c
            self.addChild(vc)
            stack.addArrangedSubview(vc.view)
            vc.view.widthAnchor.constraint(equalTo: scrollView.frameLayoutGuide.widthAnchor,constant: 0.0).isActive = true
            vc.didMove(toParent: self)
            pages.append(vc)
        }
        
        pageControl.numberOfPages = pages.count
        
        scrollView.delegate = self
        
        pageControl.addTarget(self,action: #selector(self.pgControlChange(_:)),for: .valueChanged)
    }
    
    var pgControlScroll: Bool = false
    
    @objc func pgControlChange(_ sender: UIPageControl) {
        pgControlScroll = true
        let w = scrollView.frame.size.width
        guard w != 0 else { return }
        let x = scrollView.contentOffset.x
        let cp = min(Int(round(x / w)),pages.count - 1)
        let np = sender.currentPage
        var r = CGRect.zero
        if np > cp {
            r = CGRect(x: w * CGFloat(np + 1) - 1.0,y: 0,width: 1,height: 1)
        } else {
            r = CGRect(x: w * CGFloat(np),height: 1)
        }
        scrollView.scrollRectToVisible(r,animated: true)
    }
    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        pgControlScroll = false
    }
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let w = scrollView.frame.size.width
        guard w != 0 else { return }
        let x = scrollView.contentOffset.x
        let pg = min(Int(round(x / w)),pages.count - 1)
        let v = stack.arrangedSubviews[pg]
        pageControl.backgroundColor = v.backgroundColor
        if pgControlScroll { return }
        pageControl.currentPage = pg
    }

}

class BasePageController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // add a label at each corner
        for (i,s) in ["top-left","top-right","bot-left","bot-right"].enumerated() {
            let v = UILabel()
            v.backgroundColor = UIColor(white: 0.8,alpha: 1.0)
            v.translatesAutoresizingMaskIntoConstraints = false
            v.text = s
            view.addSubview(v)
            let g = view.safeAreaLayoutGuide
            switch i {
            case 1:
                v.topAnchor.constraint(equalTo: g.topAnchor,constant: 4.0).isActive = true
                v.trailingAnchor.constraint(equalTo: g.trailingAnchor,constant: -4.0).isActive = true
            case 2:
                v.bottomAnchor.constraint(equalTo: g.bottomAnchor,constant: -4.0).isActive = true
                v.leadingAnchor.constraint(equalTo: g.leadingAnchor,constant: 4.0).isActive = true
            case 3:
                v.bottomAnchor.constraint(equalTo: g.bottomAnchor,constant: -4.0).isActive = true
                v.trailingAnchor.constraint(equalTo: g.trailingAnchor,constant: -4.0).isActive = true
            default:
                v.topAnchor.constraint(equalTo: g.topAnchor,constant: 4.0).isActive = true
                v.leadingAnchor.constraint(equalTo: g.leadingAnchor,constant: 4.0).isActive = true
            }
        }
    }
    
}

该代码添加了一个滚动视图，该视图占据了屏幕的大部分内容（带有一些填充，因此滚动视图的框架很明显），其下方为UIPageControl。

我们添加4个视图控制器作为子视图控制器，并将其视图添加到滚动视图的UIStackView中。

当您从“页面到页面”滚动时，页面控件将在您到达下一页/上一页的中途更新和更改背景颜色。

,

UIPageViewController没有任何我知道的跟踪部分滚动的机制。它基于这样的假设，即页面视图控制器已经存在，并且只有在用户完成“页面翻转”之后，您才会收到通知。

它还支持页面卷曲样式的页面翻转和侧向滚动，这将使尝试破解解决方案变得更加复杂/脆弱。