如何在UICollectionView单元格中显示活动指示器？

import UIKit

class CustomCollectionViewCell: UICollectionViewCell {
    var activityIndicator: UIActivityIndicatorView!
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        // 创建活动指示器
        activityIndicator = UIActivityIndicatorView(style: .gray)
        activityIndicator.center = contentView.center
        contentView.addSubview(activityIndicator)
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func prepareForReuse() {
        super.prepareForReuse()
        
        // 重置活动指示器的状态
        activityIndicator.stopAnimating()
    }
}

class ViewController: UIViewController, UICollectionViewDataSource {
    var collectionView: UICollectionView!
    var data: [String] = []
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建UICollectionView
        let layout = UICollectionViewFlowLayout()
        collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
        collectionView.dataSource = self
        collectionView.register(CustomCollectionViewCell.self, forCellWithReuseIdentifier: "Cell")
        view.addSubview(collectionView)
        
        // 添加数据
        data = ["Item 1", "Item 2", "Item 3", "Item 4", "Item 5"]
        
        // 刷新UICollectionView
        collectionView.reloadData()
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return data.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! CustomCollectionViewCell
        
        // 根据需要显示或隐藏活动指示器
        if indexPath.item == 2 {
            cell.activityIndicator.startAnimating()
        } else {
            cell.activityIndicator.stopAnimating()
        }
        
        return cell
    }
}