iOS6 UICollectionView 和 UIPageControl - 如何获取可见单元格

的文章如下：

swift
import UIKit
class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource {
    
    @IBOutlet weak var collectionView: UICollectionView!
    @IBOutlet weak var pageControl: UIPageControl!
    
    let cellIdentifier = "Cell"
    let data = ["1", "2", "3", "4", "5"]
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        collectionView.delegate = self
        collectionView.dataSource = self
        
        pageControl.numberOfPages = data.count
    }
    
    // MARK: - UICollectionViewDataSource
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return data.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath)
        cell.backgroundColor = .red
        return cell
    }
    
    // MARK: - UICollectionViewDelegate
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        print("Selected item at index: \(indexPath.item)")
    }
    
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let visibleCells = collectionView.visibleCells
        let visibleIndexPaths = visibleCells.map { collectionView.indexPath(for: $0)!.item }
        let currentPage = visibleIndexPaths.first ?? 0
        pageControl.currentPage = currentPage
    }
}