UIPageViewController - 检测到中途滚动到下一个视图控制器(几乎可以工作)以更改按钮颜色? [英] UIPageViewController - Detect scrolling halfway into the next view controller (almost working) to change button color?

问题描述

我有一个包含 4 个控制器的 UIPageViewController 子类的类，我试图弄清楚当我滚动到第二个视图控制器中途时如何更改按钮的颜色

I have a class that subclasses a UIPageViewController that which contains 4 controllers, I am trying to figure out how I can change color of the button as I scroll halfway to the second view controller

按钮颜色应仅在第一个控制器上有所不同

这里的代码几乎可以正常工作，但仅对第三个控制器的行为不正确，这意味着解决方案不正确.

This code here almost works but the behaviour is not correct only for the third controller which means the solution is not correct.

如果有人能提供帮助，我将不胜感激.谢谢

I Would really appreciate it if someone could help out. Thanks

    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)
        }
    }

推荐答案

即使你说你想使用 UIPageViewController，这里有一个使用 UIScrollView 的示例实现，你可能会更容易管理:

Even though you say you want to use UIPageViewController, here is an example implementation using UIScrollView that you may find easier to manage:

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, constant: 20.0),
            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, constant: 0.0),
            stack.trailingAnchor.constraint(equalTo: svCLG.trailingAnchor, constant: 0.0),
            stack.bottomAnchor.constraint(equalTo: svCLG.bottomAnchor, constant: 0.0),
            
            stack.heightAnchor.constraint(equalTo: svFLG.heightAnchor, constant: 0.0),
            
            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), y: 0, width: 1, 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
            }
        }
    }
    
}

代码添加了一个占据大部分屏幕的滚动视图(有一些填充，因此滚动视图的框架很明显)，下面有一个 UIPageControl.

The code adds a scroll view that takes up most of the screen (with some padding so the frame of the scroll view is obvious), with a UIPageControl underneath.

我们添加4个视图控制器作为子视图控制器，并将它们的视图添加到滚动视图中的一个UIStackView中.

We add 4 view controllers as child view controllers, and add their views to a UIStackView in the scroll view.

当您从页面到页面"滚动时当您进入下一页/上一页的中途时，页面控件将更新和更改背景颜色.

When you scroll from "page-to-page" the page control will update and change background color as you get half-way to the next / previous page.

这篇关于UIPageViewController - 检测到中途滚动到下一个视图控制器(几乎可以工作)以更改按钮颜色?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！