How to update a rich text box from a background worker using a delegate

Question

Ok I'm pretty new to using threads but so far I've managed to get the following:

Private Delegate Sub dlgUpdateText(text as string)

Private Sub UpdateStatus(text as string)
  If rtxStatus.InvokeRequired then
    Dim dlg as new dlgUpdateText(AddressOf UpdateStatus)
    Me.Invoke(dlg, text)
  Else
    rtxStatus.text = text
  End If
End Sub

and from my Async BackgroundWorker I call

UpdateStatus("Some text") 

which seems to work ok however in my original code (which generates errors because I'm updating the control from the wrong thread) I used the following code to append to the (rich)textbox:

rtxStatus.Select(rtxStatus.TextLength, 0)
rtxStatus.SelectionColor = Color.Red
rtxStatus.AppendText("Some error occurred gathering data")

My question is how should I modify my new code to allow me to do this rather than just replace the text? I have read several guides on using delegates but I'm still lost on a few points so I don't really know what's going on with the code I have.

Bonus questions (which probably serve best to show what needs explaining to me!):

1. What does the Delegate Sub actually do? It doesn't seem to serve any purpose other than hold the property (text) that was already passed to the main Sub (UpdateStatus)?
2. What is happening when Me.Invoke is called? Me is the current form so when I pass the Delegate Sub and the text where is it specified that the text should be passed to the rtxSTatus.Text property?
3. UpdateStatus runs in the main thread (?) and is called from one of the background worker threads so why is the Invoke even necessary or is the UpdateStatus Sub run under the background thread that called it? When I altered the text that is applied in the Else statement to see which was run it seems that Invoke is never used to change the text in the box.

Any help would be really appreciated, I'm completely baffled by this - thanks!

Answer 1

Rather than creating a delegate I would suggest using the existing methods offered from a backgroundworker. The backgroundworker provides two methods to access the main thread:

The ProgressChanged event to update the main thread during backgroundworker processing and the RunWorkerCompleted event to update the main thread once the backgroundworker process is complete.

You can find this information and how to implement it from the following link:

http://msdn.microsoft.com/en-us/library/ywkkz4s1.aspx