Listbox to and from file (XML & JSON)

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

using System.IO;
using System.Xml.Serialization;
//Install Newtonsoft with packet manager (Tools > NuGet Packet Manager > Package Manager Console)
//PM> Install-Package Newtonsoft.Json
using Newtonsoft.Json;

namespace Listbox_to_XML
{
    public partial class Form1 : Form
    {

        private string loadLocation;
        private string saveLocation;
        private List<string> tmpItems = new List<string>();
        public Form1()
        {
            InitializeComponent();
        }

        public void save_Click(object sender, EventArgs e)
        {
            /*Save dialogue formatting for selected type*/
            saveFileDialog.Title = $"Save {fileFormat.Text} File";
            saveFileDialog.Filter = $"{fileFormat.Text.ToUpper()}|*.{fileFormat.Text.ToLower()}";
            saveFileDialog.FilterIndex = 0;
            saveFileDialog.OverwritePrompt = true;
            bool save = false;
            if (saveFileDialog.ShowDialog() != DialogResult.Cancel)
            {
                saveLocation = saveFileDialog.FileName;
                save = true;
            }
            if (save)
            {
                /*Create a list with listbox items*/
                tmpItems.Clear();
                foreach (var item in listBox1.Items)
                {
                    tmpItems.Add(item.ToString());
                }

                listbox lb = new listbox(); //Create an object and insert the list
                lb.items = tmpItems;
                switch (saveLocation.Split('.')[saveLocation.Split('.').Length - 1].ToUpper())
                {
                    case "XML":
                        StreamWriter sw = new StreamWriter(saveLocation);
                        new XmlSerializer(lb.GetType()).Serialize(sw,lb); /*Write class to file as XML*/
                        sw.Close();
                        break;
                    case "JSON":
                        File.WriteAllText(saveLocation, JsonConvert.SerializeObject(lb)); /*Write class to file as JSON*/
                        break;
                    default:
                        MessageBox.Show($"Whoops, the file format you chose .{saveLocation.Split('.')[saveLocation.Split('.').Length - 1].ToLower()} isn't supported, only XML and JSON.", "Unsupported File");
                        break;
                }
            }
        }

        public void load_Click(object sender, EventArgs e)
        {
            openFileDialog.Title = "Select a File";
            openFileDialog.Filter = fileFormat.Text == "XML" ? "XML|*.xml|JSON|*.json" : "JSON|*.json|XML|*.xml";
            saveFileDialog.FilterIndex = 0;
            if (openFileDialog.ShowDialog() != DialogResult.Cancel)
            {
                loadLocation = openFileDialog.FileName;
            }
            else
            {
                loadLocation = "";
            }
            if (loadLocation != "")
            {
                listbox lb = new  listbox();
                switch (loadLocation.Split('.')[loadLocation.Split('.').Length - 1].ToUpper())
                {
                    case "XML":
                        try
                        {
                            lb = (listbox)new XmlSerializer(lb.GetType()).Deserialize(new StringReader(File.ReadAllText(loadLocation)));
                            populateListbox(lb.items);
                        }
                        catch
                        {
                            MessageBox.Show("File chosen is not in the correct format.", "Important");
                        }
                        break;
                    case "JSON":
                        try
                        {
                            lb = JsonConvert.DeserializeObject<listbox>(File.ReadAllText(loadLocation));
                            populateListbox(lb.items);
                        }
                        catch
                        {
                            MessageBox.Show("File chosen is not in the correct format.", "Important");
                        }
                        break;
                    default:
                        MessageBox.Show($"Whoops, the file format you chose .{loadLocation.Split('.')[loadLocation.Split('.').Length - 1].ToLower()} isn't supported, only XML and JSON.", "Unsupported File");
                        break;
                }
            }
        }
        private void populateListbox(List<string> items)
        {
            listBox1.Items.Clear();
            foreach (var item in items)
            {
                listBox1.Items.Add(item);
            }
        }
    }
    public class listbox /*Must be a parameterless constructor for XML*/
    {
        public List<string> items;
    }
}