如何使用swift 5在DropDown中实现多选？

import UIKit
import DropDown

class ViewController: UIViewController {
    @IBOutlet weak var dropDownButton: UIButton!
    
    let dropDown = DropDown()
    var selectedOptions: [String] = []
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 设置下拉列表的数据源
        dropDown.dataSource = ["Option 1", "Option 2", "Option 3", "Option 4", "Option 5"]
        
        // 设置下拉列表的样式
        dropDown.anchorView = dropDownButton
        dropDown.direction = .any
        dropDown.width = dropDownButton.frame.width
        
        // 设置多选功能
        dropDown.selectionAction = { [unowned self] (index: Int, item: String) in
            // 更新多选按钮或多选框的状态
            let isSelected = !self.dropDown.selectedIndices.contains(index)
            self.dropDownButton.setTitle(item, for: .normal)
            self.dropDownButton.isSelected = isSelected
            
            // 更新选中的选项数组
            if isSelected {
                self.selectedOptions.append(item)
            } else {
                if let indexToRemove = self.selectedOptions.firstIndex(of: item) {
                    self.selectedOptions.remove(at: indexToRemove)
                }
            }
        }
    }
    
    @IBAction func dropDownButtonTapped(_ sender: UIButton) {
        dropDown.show()
    }
    
    @IBAction func confirmButtonTapped(_ sender: UIButton) {
        // 在点击确定按钮时，获取选中的选项数组，并进行相应的处理
        print("Selected options: \(selectedOptions)")
    }
}