webbrowser 判断页面加载完毕

Code
this.webBrowser1.Navigate(successurl, false);

while (true)
{
if (webBrowser1.ReadyState == WebBrowserReadyState.Complete && webBrowser1.Document.GetElementsByTagName("html")[0].OuterHtml.IndexOf("logout") > 0)
{
break;
}
else
{
box.showbox("正在加载页面"+successurl+"，请稍等！");
}
}