private void button1_Click(object sender, EventArgs e)
        {
            webBrowser1.Navigate("http://www.xxx.com");
            webBrowser1.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(webBrowser1_DocumentCompleted);
        }        void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {            HtmlElementCollection buttns = webBrowser1.Document.GetElementsByTagName("button");
            foreach (HtmlElement buttn in buttns)
            {
                if (buttn.GetAttribute("name") == "add-to-cart")
                {
                    buttn.InvokeMember("click");
                    webBrowserTwo();
                }
                if (buttn.GetAttribute("id") == "checkout-now")
                {
                    MessageBox.Show("Test");
                    buttn.InvokeMember("click");
                }
            }
        }        private void webBrowserTwo()
        {
            webBrowser1.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(webBrowser1_DocumentCompleted);
        }第一次加载后 点击按钮   来到第2个页面  在这个页面就出现了问题
在未加载完成的时候就执行到MessageBox.Show("Test");
请问 跳转后的 加载完成如何 判断