您正在寻找的是一个持久会话。您对这个问题的处理方法是不正确的。您正在客户端触发提交。您要实现的目标应该在服务器端完成。
您的方案的关键是持久（存储）登录页面设置的会话和cookie；然后在您下一次请求产品信息之前，将凭证注入请求的 webRequest。
- 使用 WebRequest 对象加载登录页面。
- 存储登录页面响应标头发送的任何信息（cookie）。
- 使用提供的响应标头创建一个新的 WebRequest 对象，注入用户 ID/密码。
- 存储响应返回的任何凭据。
- 继续请求报价信息。
在不知道您尝试从哪个网站截屏的情况下，没有通用的方法可以做到这一点。但一般步骤如上。基本上，您需要为此创建一个自定义类。
此外，您需要HTMLAgilityPack来解析 HTML 节点。这是正确的方法。
编辑：添加了我的代码。碰巧我之前创建了这个类。所以，你很幸运。但是，您需要安装并引用 HTMLAgilityPack 才能使用它。您可以在以下网址下载 HAP：http ://htmlagilitypack.codeplex.com/ 如果您想做任何严重的屏幕抓取，HAP 是事实上的标准。
Public Class clsBrowserSession
'=================================================================================================================================
'This is a special Browser Post class
' Instead of just POST to a URL as per the clsWeb.fnsPostResponse()
' clsBrowserSession allows us to LOAD a page first, persist all the cookies and variables, and then only POST to the target URL.
' The reason is that some program will drop (lets say) a SessionID as an input when you first load the page.
' and when you post, without the SessionID (variable), it will reject the POST. Thus clsBrowserSession can solve this problem.
'=================================================================================================================================
' USAGE:
' Dim voBrowserSession As New clsBrowserSession
' voBrowserSession.sbLoadPage("https://xxx.yyy.net.my/publicncdenq/index.htm")
' voBrowserSession.proFormElements("UserID") = "myID"
' voBrowserSession.proFormElements("Password") = "myPassword"
' Dim vsResponseHTML As String = voBrowserSession.Post("https://xxx.yyy.net.my/publicncdenq/index.htm")
Private vbIsPostingInProgress As Boolean
Public voCookies As System.Net.CookieCollection
Public proHTMLDoc As HtmlAgilityPack.HtmlDocument
Public proFormElements As clsFormElementCollection
Public Sub sbLoadPage(pvsURL As String)
vbIsPostingInProgress = False
fnoCreateWebRequestObject().Load(pvsURL)
End Sub
Public Function Post(pvsURL As String) As String
vbIsPostingInProgress = True
fnoCreateWebRequestObject().Load(pvsURL, "POST")
Return proHTMLDoc.DocumentNode.InnerHtml
End Function
Private Function fnoCreateWebRequestObject() As HtmlAgilityPack.HtmlWeb
Dim voWeb As New HtmlAgilityPack.HtmlWeb
voWeb.UseCookies = True
voWeb.PreRequest = New HtmlAgilityPack.HtmlWeb.PreRequestHandler(AddressOf event_OnPreRequest)
voWeb.PostResponse = New HtmlAgilityPack.HtmlWeb.PostResponseHandler(AddressOf event_OnAfterResponse)
voWeb.PreHandleDocument = New HtmlAgilityPack.HtmlWeb.PreHandleDocumentHandler(AddressOf event_OnPreHandleDocument)
Return voWeb
End Function
Private Sub sbAddPostDataTo(pvoRequest As Net.HttpWebRequest)
Dim vsPayload As String = proFormElements.fnsAssemblePostPayload()
Dim vabyteBuffer As Byte() = Text.Encoding.UTF8.GetBytes(vsPayload.ToCharArray())
pvoRequest.ContentLength = vabyteBuffer.Length
pvoRequest.ContentType = "application/x-www-form-urlencoded"
pvoRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.97 Safari/537.11"
pvoRequest.GetRequestStream().Write(vabyteBuffer, 0, vabyteBuffer.Length)
End Sub
Private Sub sbAddvoCookiesTo(pvoRequest As Net.HttpWebRequest)
If (Not IsNothing(voCookies)) Then
If voCookies.Count > 0 Then pvoRequest.CookieContainer.Add(voCookies)
End If
End Sub
Private Sub sbSaveCookiesFrom(pvoResponse As Net.HttpWebResponse)
If pvoResponse.Cookies.Count > 0 Then
If IsNothing(voCookies) Then voCookies = New Net.CookieCollection
voCookies.Add(pvoResponse.Cookies)
End If
End Sub
Private Sub sbSaveHtmlDocument(pvoHTMLDocument As HtmlAgilityPack.HtmlDocument)
proHTMLDoc = pvoHTMLDocument
proFormElements = New clsFormElementCollection(proHTMLDoc)
End Sub
Protected Function event_OnPreRequest(pvoRequest As Net.HttpWebRequest) As Boolean
sbAddvoCookiesTo(pvoRequest)
If vbIsPostingInProgress Then sbAddPostDataTo(pvoRequest)
Return True
End Function
Protected Sub event_OnAfterResponse(pvoRequest As System.Net.HttpWebRequest, pvoResponse As Net.HttpWebResponse)
sbSaveCookiesFrom(pvoResponse)
End Sub
Protected Sub event_OnPreHandleDocument(pvoHTMLDocument As HtmlAgilityPack.HtmlDocument)
sbSaveHtmlDocument(pvoHTMLDocument)
End Sub
'-----------------------------------------------------------------------------------------------------
'Form Elements class
' Note: This element class will only capture (any) INPUT elements only, which should be enough
' for most cases. It can be easily modified to add other SELECT, TEXTAREA, etc voInputs
'-----------------------------------------------------------------------------------------------------
Public Class clsFormElementCollection
Inherits Dictionary(Of String, String)
Public Sub New(htmlDoc As HtmlAgilityPack.HtmlDocument)
Dim voInputs As Collections.Generic.IEnumerable(Of HtmlAgilityPack.HtmlNode) = htmlDoc.DocumentNode.Descendants("input")
For Each voInput As HtmlAgilityPack.HtmlNode In voInputs
Dim vsName = voInput.GetAttributeValue("name", "undefined")
Dim vsValue = voInput.GetAttributeValue("value", "")
If vsName <> "undefined" Then Add(vsName, vsValue)
Next
End Sub
Public Function fnsAssemblePostPayload() As String
Dim sb As New Text.StringBuilder
For Each voKeyValuePair In Me
Dim vsValue = System.Web.HttpUtility.UrlEncode(voKeyValuePair.Value)
sb.Append("&" & voKeyValuePair.Key & "=" & vsValue)
Next
Return sb.ToString.Substring(1)
End Function
End Class
End Class
只需将上面的内容变成一个类对象并实例化它。用法示例在评论中。你想要vsResponseHTML字符串。