为什么使用了BackgroundWorker，还是很卡，界面还是出现未响应
大家帮我看看了，不知道哪里出问题，应该如何修改？

BackgroundWorker bw = null;

        public Form3()
        {
            InitializeComponent();

            bw = new BackgroundWorker();
            bw.WorkerSupportsCancellation = true;
            bw.DoWork += new DoWorkEventHandler(bw_DoWork);
            bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
        }

        void bw_DoWork(object sender, DoWorkEventArgs e)
        {
            for (int i = 1; i < 100; i++)
            {
                if (bw.CancellationPending)
                {
                    e.Cancel = true;
                    break;
                }

                this.Invoke((MethodInvoker)delegate
                {
                    this.richTextBox1.Text += Environment.NewLine + String.Format("第{0}次测试是否联网：{1}", i.ToString(), IsWWW("http://www.baidu.com"));
                    Thread.Sleep(2000);
                });
            }
        }

        void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            this.richTextBox1.Text += "执行完毕";
        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.button1.Enabled = false;
            bw.RunWorkerAsync();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            this.button1.Enabled = true; 
 
            this.button2.Enabled = false;

            bw.CancelAsync();
        }

        private void richTextBox1_TextChanged(object sender, EventArgs e)
        {
            RichTextBox textbox = (RichTextBox)sender;

            textbox.SelectionStart = textbox.Text.Length;
            textbox.ScrollToCaret();
        }


        private bool IsWWW(string url)
        {
            try
            {
                new WebClient().DownloadString(url);
                return true;
            }
            catch (Exception ex)
            {
                return false;
            }
        }

[解决办法]
Thread.Sleep(2000);
把UI主线程给睡眠了，当然卡了，这个删掉。
[解决办法]
会不会是测试联网那里运行慢了
bw.CancellationPending

还有你看下一般连到多少次就可以跳出连接了
[解决办法]
if (bw.CancellationPending)
{
e.Cancel = true;
break;
}

this.Invoke((MethodInvoker)delegate
{
this.richTextBox1.Text += Environment.NewLine + String.Format("第{0}次测试是否联网：{1}", i.ToString(), IsWWW("http://www.baidu.com"));
});
Thread.Sleep(2000);