如何在swift3中显示UICollectionView中两个不同的单元格

import UIKit

class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    
    let reuseIdentifier1 = "Cell1"
    let reuseIdentifier2 = "Cell2"
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建UICollectionViewFlowLayout对象，并设置布局属性
        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .vertical
        layout.minimumLineSpacing = 10
        layout.minimumInteritemSpacing = 10
        
        // 创建UICollectionView对象，并设置数据源和委托
        let collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
        collectionView.dataSource = self
        collectionView.delegate = self
        
        // 注册单元格
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier1)
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier2)
        
        // 添加到视图
        view.addSubview(collectionView)
    }
    
    // MARK: - UICollectionViewDataSource
    
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 2
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        if section == 0 {
            return 5 // 第一个分区的单元格数量
        } else {
            return 3 // 第二个分区的单元格数量
        }
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        var cell: UICollectionViewCell
        
        if indexPath.section == 0 {
            cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier1, for: indexPath)
            cell.backgroundColor = .red
        } else {
            cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier2, for: indexPath)
            cell.backgroundColor = .blue
        }
        
        return cell
    }
    
    // MARK: - UICollectionViewDelegateFlowLayout
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        if indexPath.section == 0 {
            return CGSize(width: 100, height: 100) // 第一个分区的单元格大小
        } else {
            return CGSize(width: 150, height: 150) // 第二个分区的单元格大小
        }
    }
}