带有 UIPageControl 的无限 UICollectionview

Question

在下面给定的代码中，我可以简单地无限滚动单元格。页面控件似乎至少在向前滚动（屏幕右侧）时也可以工作。但坦率地说，当我向左滚动时，我看到了 3 个项目的奇怪索引路径跳转（顺便说一下，我的数据源有 3 个项目用于测试目的）。在屏幕上我没有发现任何问题。但是页面控件似乎冻结了一会儿，然后再次开始工作，但是发生了转变，并且显示了错误的单元格点。有任何想法吗？感谢您的帮助...

import UIKit

class HomeHeaderCell: CategoryCell {

    private let cellId = "cellId"
    private var timer: Timer?
    private let infiniteSize = 1000
    private var onlyOnce = true

    // ...

    let pageControl: UIPageControl = {
        let rect = CGRect(origin: .zero, size: CGSize(width: 200, height: 50))
        let pc = UIPageControl(frame: rect)
        pc.currentPage = 0
        pc.numberOfPages = 3
        pc.pageIndicatorTintColor = .gray
        pc.currentPageIndicatorTintColor = .red
        pc.isUserInteractionEnabled = false
        return pc
    }()

    override func setupViews() {

        addSubview(baseCollectionView)
        addSubview(pageControl)


        baseCollectionView.delegate = self
        baseCollectionView.dataSource = self
        baseCollectionView.register(HeaderCell.self, forCellWithReuseIdentifier: cellId)

        baseCollectionView.backgroundColor = .white
        baseCollectionView.isPagingEnabled = true
        baseCollectionView.isScrollEnabled = true

        baseCollectionView.showsHorizontalScrollIndicator = false


        baseCollectionView.anchor(top: topAnchor, leading: leadingAnchor, bottom: bottomAnchor, trailing: trailingAnchor)
        pageControl.anchor(top: nil, leading: leadingAnchor, bottom: bottomAnchor, trailing: nil, padding: UIEdgeInsets(top: 0, left: 16, bottom: 0, right: 0))
    }


    @objc func autoScroll() {
        guard let currentItemNumber = baseCollectionView.indexPathsForVisibleItems.first?.item  else { return }
        let nextItemNumber = currentItemNumber + 1
        let nextIndexPath = IndexPath(item: nextItemNumber, section: 0)
        baseCollectionView.scrollToItem(at: nextIndexPath, at: .left, animated: true)
    }

    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        stopTimer()
    }
    func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        startTimer()
    }

    func startTimer() {
        timer = Timer.scheduledTimer(timeInterval: 4.0, target: self, selector: #selector(autoScroll), userInfo: nil, repeats: true)
    }

    func stopTimer() {
        timer?.invalidate()
        timer = nil
    }

    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return infiniteSize
    }

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! HeaderCell

        // Maybe can be done more elegantly...
        if let foods = foodCategory?.foods {
            let numberOfFood = indexPath.item % foods.count
            cell.food = foods[numberOfFood]
            pageControl.currentPage = numberOfFood
            print(numberOfFood)
        }
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
        if onlyOnce  {
            let middleIndex = IndexPath(item: Int (infiniteSize / 2), section: 0)
            baseCollectionView.scrollToItem(at: middleIndex, at: .centeredHorizontally, animated: false)
            startTimer()
            onlyOnce = false
        }
    }

    override func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: frame.width, height: frame.height)
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
        return 0
    }

    private class HeaderCell: ItemCell {

        override func setupViews() {
            addSubview(imageView)

            imageView.layer.cornerRadius = 0
            imageView.layer.borderColor = UIColor(white: 0.5, alpha: 0.5).cgColor
            imageView.layer.borderWidth = 0.5

            imageView.anchor(top: topAnchor, leading: leadingAnchor, bottom: bottomAnchor, trailing: trailingAnchor)
        }
    }

}

Answer 1

我解决了我自己的问题。这是您应该应用的代码。前两个方法是 UICollectionView 附带的 UIScrollView 方法，顺便说一下，它是 UIScrollView 的子类。 updatePageControl 方法是我为保持代码简洁而编写的方法。希望这会有所帮助...

func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
    updatePageControl(scrollView: scrollView)
}

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    updatePageControl(scrollView: scrollView)
}
func updatePageControl(scrollView: UIScrollView) {
    let pageNumber = round(scrollView.contentOffset.x / scrollView.bounds.size.width)
    guard let count = foodCategory?.foods?.count else {return}
    let currentPageNumber = Int(pageNumber) % count
    pageControl.currentPage = currentPageNumber
}