Creating a webbrowser control in a background thread in backgroundworker

Question

Is it possible to create a WebBrowser control in a background thread in BackgroundWorker?

Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
    Using web1 As New WebBrowser

    End Using
End Sub

This throws the following error:

ActiveX control '8856f961-340a-11d0-a96b-00c04fd705a2' cannot be instantiated because the current thread is not in a single-threaded apartment.

Does anyone know a way to create a background WebBrowser? I would like to do it to extract info from websites then spit out the various HTML DOM arrays

Answer 1

The thread that the Webbrowser runs in must be ApartmentState.STA. From a BackgroundWorker thread you'll have to use Invoke on a UI object and add the Webbrowser in that context.

I don't think you really need to run the WebBrowser object in a background thread anyway. All of it's functionality is handled asynchronously with events.

Answer 2

You can also write a wrapper class, that instantiates the web browser control, create methods that wrap your extraction functions, and fire off the results through public events.

From here you just create a new instance of your wrapper, and add it to the ThreadPool.

Remember to do proper owner-thread invoking to avoid cross-thread exceptions ;)

Answer 3

Having been down both roads, I would recommend WatiN, an open source library to automate IE and Firefox. The WebBrowser control is good for displaying content, but for anything more complex it becomes a big hassle.