BackgroundWorker 后台线程

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Threading;
using System.Windows.Forms;
using System.Xml;


namespace UseBackgroundWorker
{
    public partial class Form1 : Form
    {
        private XmlDocument document = null;
        public Form1()
        {
            InitializeComponent();
        }

        private void dowloadButton_Click(object sender, EventArgs e)
        {
            this.backgroundWorker1.RunWorkerAsync();

            // Disable the button for the duration of the download.
            this.dowloadButton.Enabled = false;

            // Wait for the BackgroundWorker to finish the download.
            while (this.backgroundWorker1.IsBusy)
            {
                // Keep UI messages moving, so the form remains 
                // responsive during the asynchronous operation.
                Application.DoEvents();
            }

            // The download is done, so enable the button.
            this.dowloadButton.Enabled = true;

        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            document = new XmlDocument();

            // Replace this file name with a valid file name.
            document.Load(@"http://www.tailspintoys.com/sample.xml");

            // Uncomment the following line to
            // simulate a noticeable latency.
            //Thread.Sleep(5000);

        }

        private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (e.Error == null)
            {
                MessageBox.Show(document.InnerXml, "Download Complete");
            }
            else
            {
                MessageBox.Show(
                    "Failed to download file",
                    "Download failed",
                    MessageBoxButtons.OK,
                    MessageBoxIcon.Error);
            }

        }
    }
}