private void btn_Add_Click(object sender, EventArgs e)
{
 string sUrl = txb_Url.Text.Trim();
 if (sUrl.Length > 0)
 {
  webBrowser1.Navigate(sUrl);
 }
}
private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
 HtmlElement ClickBtn = null;
 if (e.Url.ToString().ToLower().IndexOf("login.aspx") > 0)
 {
  HtmlDocument doc = webBrowser1.Document;
  for (int i = 0; i < doc.All.Count; i++)
  {
   if(doc.All[i].TagName.ToUpper().Equals("INPUT"))
   {
    switch(doc.All[i].Name)
    {
     case "txtUserName":
      doc.All[i].InnerText = "xxxx@yy.com"; // 用户名
      break;
     case "txtPassword":
      doc.All[i].InnerText = "zzzzzz"; // 密码
      break;
     case "btnSubmit":
      ClickBtn = doc.All[i];
      break;
    }
   }
  }
  ClickBtn.InvokeMember("Click"); // 点击“登录”按钮
 }
}