c# - 指定的转换无效。 C# 网页浏览器

Question

url="https://ipv4.google.com/sorry/IndexRedirect?continue=https://www.google.com/search%3Fq%3Dstackoverflow%2B%26rlz%3D1C1KMZB_enTR561TR561%26oq%3Dstac%26aqs%3Dchrome.1.69i59l3j69i60j69i57j69i60.5208j0j7%26sourceid%3Dchrome%26espv%3D210%26es_sm%3D122%26ie%3DUTF-8";

webBrowser1.Navigate(url);

if (url.Contains("ipv4.google.com"))
{
    frm2.ShowDialog();
    Application.DoEvents();
    webBrowser1.Document.GetElementById("captcha").SetAttribute("value", frm2.code);
    webBrowser1.Document.GetElementById("submit").InvokeMember("click");
}

异常(exception)是:

Specified cast is not valid.

在

webBrowser1.Document.GetElementById("captcha").SetAttribute("value", frm2.code);

Answer 1

在准备加载时使用文档。

string url = "https://ipv4.google.com/sorry/IndexRedirect?continue=https://www.google.com/search%3Fq%3Dstackoverflow%2B%26rlz%3D1C1KMZB_enTR561TR561%26oq%3Dstac%26aqs%3Dchrome.1.69i59l3j69i60j69i57j69i60.5208j0j7%26sourceid%3Dchrome%26espv%3D210%26es_sm%3D122%26ie%3DUTF-8";

WebBrowser webBrowser1 = new WebBrowser();
this.Controls.Add(webBrowser1);
webBrowser1.Dock = DockStyle.Fill;

webBrowser1.Navigate(url);

if (url.Contains("ipv4.google.com"))
{
    webBrowser1.DocumentCompleted += handler;
}

private void handler(object sender, WebBrowserDocumentCompletedEventArgs e)
    {
        frm2.ShowDialog();
        webBrowser1.Document.GetElementById("captcha").SetAttribute("value", frm2.code);
        webBrowser1.Document.GetElementById("submit").InvokeMember("click");

        webBrowser1.DocumentCompleted -= handler;
    };