VB.NET Background Worker check propriety of the form TargetInvocationException

Question

I'm working on a program that should find some image's urls from a website and should download them, i already wrote the parsing code and the downloading code, and it work, but since i noticed it's really slow i thought that it would be better if i make it work async from the form, so i created 2 background worker:

1) The parser

2) The downloader

When the parser starts the downloader starts too, the parser should add urls to a listbox, and the downloader should download them and delete from the list, i don't think it will be a problem to manage that, my real problem is... that i never used background worker...

The parser should load the page in a Webbrowser, than parse the images, but when i call the function navigate on the webbrowser... it stop giving me a TargetInvocationException.

I searched online, and from what i have seen it seems that backgrond workers cannot directly access to proprieties and methods of the GUI controls, from what i've understand it shold use Invoke, so i created a function that do all the work, and it check if the browser is in another thread or is in this thread by doing this:

Sub parse(ByVal url As String)
  If wb.InvokeRequired Then 'wb is the Webbrowser
    wb.Invoke(New Action(AddressOf prova))
    Return
  End If
  'Navigate to the url, wait for browser to complete loading then do the parsing
End Sub

Now my problems are two:

1)The invokerequired propriety value is false even if i call the method from the worker, so the invoke is not called and it still give me the same exception

2)If i call invoke i should force the method to run in the GUI thread, right? If so... shouldn't it slow my program as before?

Answer 1

I did it alone, the problem was that i created the components in runtime, so I should have created the handles for the components, it was enough to do something like this after creating the components:

If Not wb.IsHandleCreated Then
  Dim handle As IntPtr = wb.Handle
End If

The variable handle is useless, but calling the handle propriety of the component it force the component to create the handle, that's why I made that assignment.