VB.NET WebBrowser Control Programmatically Filling Form After Changing User-Agent (Object reference not set to an instance of an object.) - vb.net

Question

I'm working on a project where I have a WebBrowser control which needs to have a custom user-agent set, then go to Google and fill out the search box, click the search button, then click a link from the search results. Unfortunately I can't use HTTPWebRequest, it has to be done with the WebBrowser control.
Before I added the code to change the user-agent, everything worked fine. Here's the code that I have:
Imports System.Runtime.InteropServices
Public Class Form1
<DllImport("urlmon.dll", CharSet:=CharSet.Ansi)> _
Private Shared Function UrlMkSetSessionOption(dwOption As Integer, pBuffer As String, dwBufferLength As Integer, dwReserved As Integer) As Integer
End Function
Const URLMON_OPTION_USERAGENT As Integer = &H10000001
Public Sub ChangeUserAgent(Agent As String)
UrlMkSetSessionOption(URLMON_OPTION_USERAGENT, Agent, Agent.Length, 0)
End Sub
Private Sub btnGo_Click(sender As Object, e As EventArgs) Handles btnGo.Click
ChangeUserAgent("Fake User-Agent")
wb.Navigate("http://www.google.com", "_self", Nothing, "User-Agent: Fake User-Agent")
End Sub
Private Sub wb_DocumentCompleted(ByVal sender As Object, ByVal e As WebBrowserDocumentCompletedEventArgs) Handles wb.DocumentCompleted
Dim Source As String = wb.Document.Body.OuterHtml
Dim Uri As String = wb.Document.Url.AbsoluteUri
If Uri = "http://www.google.com/" Then
wb.Document.GetElementById("lst-ib").SetAttribute("value", "browser info")
wb.Document.All("btnK").InvokeMember("click")
End If
If Uri.Contains("http://www.google.com/search?") Then
Dim TheDocument = wb.Document.All
For Each curElement As HtmlElement In TheDocument
Dim ctrlIdentity = curElement.GetAttribute("innerText").ToString
If ctrlIdentity = "BROWSER-INFO" Then
curElement.InvokeMember("click")
End If
Next
End If
End Sub
End Class
The problem lies in the following code:
wb.Document.GetElementById("lst-ib").SetAttribute("value", "browser info")
wb.Document.All("btnK").InvokeMember("click")
I thought the problem might be that the page not being fully loaded (frame issue) but I put the offending code in a timer to test, and got the same error. Any help would be much appreciated.

Answer 1

Do you realize .All("btnK") returns a collection? So, you are doing .InvokeMember("click") on a Collection :). You cannot do that, you can only do .InvokeMember("click") on an element for obvious reasons!
Try this:
wb.Document.All("btnK").Item(0).InvokeMember("click")
The .Item(0) returns the first element in the collection returned by .All("btnK"), and since there will only probably be one item returned, since there is only one on the page, you want to do the InvokeMember on the first item, being .Item(0).
May I ask what it is you are developing?
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