如何使集合视图单元格多列？

import UIKit

class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    
    @IBOutlet weak var collectionView: UICollectionView!
    
    let itemsPerRow: CGFloat = 3 // 每行显示的单元格数量
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 设置集合视图的代理和数据源
        collectionView.delegate = self
        collectionView.dataSource = self
        
        // 设置流式布局
        let layout = UICollectionViewFlowLayout()
        layout.minimumInteritemSpacing = 10 // 单元格之间的水平间距
        layout.sectionInset = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10) // 边距
        collectionView.collectionViewLayout = layout
    }
    
    // MARK: - UICollectionViewDataSource
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 20 // 单元格数量
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath)
        // 配置单元格的内容
        cell.backgroundColor = UIColor.blue
        return cell
    }
    
    // MARK: - UICollectionViewDelegateFlowLayout
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let paddingSpace = layout.sectionInset.left + layout.sectionInset.right + (layout.minimumInteritemSpacing * (itemsPerRow - 1))
        let availableWidth = collectionView.frame.width - paddingSpace
        let widthPerItem = availableWidth / itemsPerRow
        return CGSize(width: widthPerItem, height: widthPerItem)
    }
}