C# webbrowser判断页面是否加载完毕

private void Form1_Load(object sender, EventArgs e)
        {
            webalipay.Url = new Uri("https://authzth.alipay.com/login/homeB.htm");
            webalipay.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(wb_DocumentCompleted);//加载完成后的事件
        }
        /// <summary>
        /// 页面加载完事件
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void wb_DocumentCompleted(object sender, EventArgs e)
        {
            //这个就是当网页载入完毕后要进行的操作
            hdoc = webalipay.Document;
            HtmlElement imgcode = Function.WebTools.GetElement_Id(hdoc, "J-checkcode-img");
            codeurl = imgcode.GetAttribute("src");
            piccode.Imagelocatio{过滤}n = codeurl;
        }