asp.net 驗證網址的合法性

  private void button1_Click(object sender, EventArgs e)
        ...{         
            Regex cRegex = new Regex(@"^http://([w-]+.)+[w-]+(/[w-./?%&=]*)?$");
            if (cRegex.Match(urltext.Text.Trim()).Value != "")
            ...{
                webBrowser1.Url = new Uri(urltext.Text.Trim());
            }
            else
            ...{
                MessageBox.Show("沒有輸入網址或網址不正確！");
                urltext.Text = null;
            }
        }