Multithreaded File/Folder Finder

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

namespace FileFind
{
    /// <summary>
    ///   User interface to display a list of folders and disk drives to be excluded
    /// when a search is performed. The information is stored in ConfigInfo.
    /// </summary>
    public partial class IgnoreFolders : Form
    {
        private ConfigInfo configInfo = new ConfigInfo();
        private bool isDirty = false;   //determines if ConfigInfo class is to be updated
                                        //when this form closes

        public IgnoreFolders()
        {
            InitializeComponent();
            this.Font = configInfo.UseFont;
        }

        void AddNewFolder(string newIgnore)
        {
            string str = newIgnore.Replace('\\', '/');
            int index = listBox1.FindStringExact(str, -1);    // Search starting from index -1:
            if (index == -1)
            {
                listBox1.Items.Add(str);
                isDirty = true;
            }
        } //ends void AddNewFolder(...

        private void IgnoreFolders_Load(object sender, EventArgs e)
        {
            this.Text = configInfo.ProductName + " - Exclude disk(s) or folder(s)";
            msgLabel.Text = "";
            //load the current ignore folders array
            listBox1.BeginUpdate(); // Shutdown the painting of the ListBox
            foreach (string str in configInfo.IgnoreFolders)
            { listBox1.Items.Add(str); }
            listBox1.EndUpdate();   // Allow the ListBox to repaint and display the remaining items
            textBox1.Select();
        }

        private void addButton_Click(object sender, EventArgs e)
        {   //Add a new disk or folder
            string newIgnore = textBox1.Text.Trim();
            if ((newIgnore.IndexOf("*") > -1) || (newIgnore.IndexOf("?") > -1))
                msgLabel.Text = "Selection characters (asterisk and question mark) are not allowed";
            else
            {
                AddNewFolder(newIgnore);
                textBox1.Text = 
                msgLabel.Text = "";
            }
            textBox1.Focus();
        }

        private void deleteButton_Click(object sender, EventArgs e)
        {   //Delete selected folders
            if (-1 == listBox1.SelectedIndex)
                return;
            ArrayList remove_folders = new ArrayList();
            listBox1.BeginUpdate(); // Shutdown the painting of the ListBox as items are deleted
            for (int i = 0; i < listBox1.SelectedItems.Count; ++i)
                remove_folders.Add(listBox1.SelectedItems[i].ToString());
            //listBox1.Items.RemoveAt(listBox1.SelectedItems);
            if (remove_folders.Count != 0)
                isDirty = true;
            foreach (string str in remove_folders)
                listBox1.Items.Remove(str);
            listBox1.EndUpdate();   // Allow the ListBox to repaint and display the remaining items
            listBox1.Invalidate();
            textBox1.Focus();
        }

        private void cancelButton_Click(object sender, EventArgs e)
        {   //Cancel all changes
            isDirty = false;
            this.DialogResult = DialogResult.Cancel;
            this.Close();
        }


        private void exitButton_Click(object sender, EventArgs e)
        {
            this.DialogResult = DialogResult.OK;
            this.Close();
        }

        private void defaultsButton_Click(object sender, EventArgs e)
        {   //reset ignored folders to defaults
            listBox1.Items.Clear();
            ArrayList ignoreFolders = new ArrayList();
            ignoreFolders = configInfo.DefaultFolders;
            foreach (string str in ignoreFolders)
                listBox1.Items.Add(str);
            isDirty = true;
        }

        private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            if ((char)Keys.Enter == e.KeyChar)
            { //treat as Add button
                string newIgnore = textBox1.Text;
                if ((newIgnore.IndexOf("*") > -1) || (newIgnore.IndexOf("?") > -1))
                    msgLabel.Text = "Wild card selection characters are not allowed";
                else
                {
                    AddNewFolder(textBox1.Text);
                    textBox1.Text = null;
                    msgLabel.Text = " ";
                    e.Handled = true;
                }
                textBox1.Focus();
            }
        }

        private void IgnoreForm_Closing(object sender, FormClosingEventArgs e)
        {
            if (DialogResult.Cancel != this.DialogResult)
            {
                this.DialogResult = DialogResult.OK;
                if (isDirty)
                {
                    ArrayList saveExcludes = new ArrayList();
                    for (int i = 0; i < listBox1.Items.Count; ++i)
                        saveExcludes.Add(listBox1.Items[i].ToString());
                    configInfo.IgnoreFolders = saveExcludes;
                }
            }
        }
    }
}