如何将2D数组填充到CollectionView上？

import UIKit

class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    var collectionView: UICollectionView!
    var data: [[Int]] = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] // 示例2D数组数据
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建CollectionView并设置布局
        let layout = UICollectionViewFlowLayout()
        collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
        collectionView.dataSource = self
        collectionView.delegate = self
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "Cell")
        view.addSubview(collectionView)
    }
    
    // 返回2D数组的行数
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return data.count
    }
    
    // 返回指定行的列数
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return data[section].count
    }
    
    // 填充数据到单元格
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath)
        let value = data[indexPath.section][indexPath.item]
        cell.backgroundColor = UIColor.gray
        cell.textLabel?.text = "\(value)"
        return cell
    }
    
    // 自定义单元格大小
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let width = collectionView.bounds.width / CGFloat(data[indexPath.section].count)
        return CGSize(width: width, height: width)
    }
}