如何在关闭窗体时保存列表框的值(多选)？

using System;
using System.Collections.Generic;
using System.IO;
using System.Windows.Forms;

public partial class MainForm : Form
{
    private List<string> selectedItems = new List<string>();

    public MainForm()
    {
        InitializeComponent();
    }

    private void MainForm_Load(object sender, EventArgs e)
    {
        LoadSavedItems();
    }

    private void buttonSaveAndClose_Click(object sender, EventArgs e)
    {
        SaveSelectedItems();
        this.Close();
    }

    private void LoadSavedItems()
    {
        // 从文件或数据库加载保存的项
        string savedItems = File.ReadAllText("savedItems.txt");
        selectedItems = new List<string>(savedItems.Split(','));
        UpdateListBox();
    }

    private void SaveSelectedItems()
    {
        // 将选定的项保存到文件或数据库
        string itemsToSave = string.Join(",", selectedItems);
        File.WriteAllText("savedItems.txt", itemsToSave);
    }

    private void UpdateListBox()
    {
        listBox.Items.Clear();
        listBox.Items.AddRange(selectedItems.ToArray());
    }

    private void listBox_SelectedIndexChanged(object sender, EventArgs e)
    {
        selectedItems.Clear();
        foreach (var item in listBox.SelectedItems)
        {
            selectedItems.Add(item.ToString());
        }
    }
}