Wie senden Sie Schlüssel an die Website mit ihren Element-IDs in C # ASP.Net?

Ich mache etwas ähnliches, aber ich bekomme die Seite html manuell.

// do webrequest stuff and return raw html
string html = DemoDoHttpGet(url, cookieContainer);

// I'm hitting an asp.net page so I have to repeat a bunch of values back to the server
// key is the "name" attribute of an element i want to find in the html
// i gathered these manually by watching a normal exchange with fiddler
var fields = new Dictionary<string, string>();
fields.Add(System.Web.HttpUtility.UrlDecode("__LASTFOCUS"), string.Empty);
fields.Add(System.Web.HttpUtility.UrlDecode("__EVENTTARGET"), string.Empty);
fields.Add(System.Web.HttpUtility.UrlDecode("__EVENTARGUMENT"), string.Empty);
fields.Add(System.Web.HttpUtility.UrlDecode("__VIEWSTATE"), string.Empty);
fields.Add(System.Web.HttpUtility.UrlDecode("__EVENTVALIDATION"), string.Empty);
fields.Add(System.Web.HttpUtility.UrlDecode("ctl00%24ContentPlaceHolder1%24Login1%24LoginButton"), string.Empty);

// this method searches the html for elements with the given names and updates
// the value for each item in the field collection with the value sent from the server
Scraper.GetFieldValues(fields, html);

/* looks kind of like this

        var doc = new HtmlAgilityPack.HtmlDocument();
        doc.LoadHtml(html);

        var names = new List<string>();
        foreach (var ditem in fields)
        {
            names.Add(ditem.Key);
        }

        foreach (var nitem in names)
        {
            // find items, read value

            string xpath = string.Format("//*[@name=\"{0}\"]", (nitem));
            var nodes = doc.DocumentNode.SelectNodes(xpath);

            // if node found read whatever attribute is appropriate,
            // write value back to fields collection

*/

// here i'm manually providing values for login username/password
fields.Add(System.Web.HttpUtility.UrlDecode(
    "ctl00%24ContentPlaceHolder1%24Login1%24UserName"), "my@email.aaa");
fields.Add(System.Web.HttpUtility.UrlDecode(
    "ctl00%24ContentPlaceHolder1%24Login1%24Password"), "mypassword");

// another webrequest to post back to the server

var request2 = (HttpWebRequest)WebRequest.Create(url);
request2.CookieContainer = cookieContainer;
request2.Method = "POST";
request2.ContentType = "application/x-www-form-urlencoded";

var args = new StringBuilder();
foreach (var item in fields)
{
    args.Append(System.Web.HttpUtility.UrlEncode(item.Key));
    args.Append("=");
    args.Append(System.Web.HttpUtility.UrlEncode(item.Value));
    args.Append("&");
}

using (System.IO.StreamWriter writer = 
    new System.IO.StreamWriter(request2.GetRequestStream()))
{
    writer.Write(args.ToString().TrimEnd('&'));
}

string html;
using (var response2 = (System.Net.HttpWebResponse)request2.GetResponse())
using (var rdr2 = new System.IO.StreamReader(response2.GetResponseStream()))
{
    html = rdr2.ReadToEnd();
}