BackgroundWorker bw = new BackgroundWorker();

        public MainWindow()

        {

            InitializeComponent();

            bw.WorkerReportsProgress = true;

            bw.WorkerSupportsCancellation = true;

            bw.DoWork += bw_DoWork;

            bw.ProgressChanged += bw_ProgressChanged;

            bw.RunWorkerCompleted += bw_RunWorkerCompleted;

        }

        void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)

        {

            this.txtMsg.Text = "下载完成";

        }

        void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)

        {

            this.mySlider.Value = (double)e.ProgressPercentage / ;

            this.txtMsg.Text = ((double)e.ProgressPercentage / ).ToString();

        }

        void bw_DoWork(object sender, DoWorkEventArgs e)

        {

            for (int i = ; i < ; i++)

            {

                if (bw.CancellationPending == true)

                {

                    e.Cancel = true;

                    return;

                }

                bw.ReportProgress(i);

                Thread.Sleep(TimeSpan.FromSeconds());

            }

        }

        private void btnStart_Click(object sender, RoutedEventArgs e)

        {

            bw.RunWorkerAsync();

        }

        private void btnCancel_Click(object sender, RoutedEventArgs e)

        {

            bw.CancelAsync();

        }