vb.net - how do i fix crossthreading with background worker - vb.net

Question

In VB.Net I've created a background worker which seems to work. It is set up like this:
Private bw As BackgroundWorker = New BackgroundWorker
Public Sub construct_configure()
bw.WorkerReportsProgress = True
bw.WorkerSupportsCancellation = True
AddHandler bw.DoWork, AddressOf bw_DoWork
AddHandler bw.ProgressChanged, AddressOf bw_ProgressChanged
AddHandler bw.RunWorkerCompleted, AddressOf bw_RunWorkerCompleted
end sub
Then I have the doWork Sub set up like this:
Private Sub bw_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
' create the picture box
pic_holder = New PictureBox()
' Show GIF and disable whatever you need to
With pic_holder
.Image = My.Resources.counter_gif
.Size = New Size(200, 100)
.Location = New Point(0, 0)
.Visible = True
.BackColor = Color.Red
End With
Main.Controls.Add(pic_holder)
pic_holder.BringToFront()
MessageBox.Show("worker started")
End Sub
The message box shows up when I click on my button to call the Sub, but the animated gif never does. I'm trying to simply set up an indicator that there is some background work going on. The gif shows up when I set it up in the parent sub.
Also, I'd like to place the gif in a panel that already exists, but every time I try to, I get a cross threading error that says the panel was created in another thread. How can I get around that?
Thanks.

Answer 1

It's recommended that if you want to invoke the main form you should do this in the ProgressChanged event. The bw_ProgressChanged is called on the same thread as the main form.
Private Sub bw_DoWork(sender As Object, e As DoWorkEventArgs) Handles bw.DoWork
'WORKER THREAD, do not invoke main form.
Dim worker As BackgroundWorker = CType(sender, BackgroundWorker)
'Report start
worker.ReportProgress(0)
'Do some work...
Threading.Thread.Sleep(5000)
'Report end.
worker.ReportProgress(100)
End Sub
Private Sub bw_ProgressChanged(sender As Object, e As ProgressChangedEventArgs) Handles bw.ProgressChanged
'MAIN THREAD, safe to invoke main form.
If (e.ProgressPercentage = 0) Then
'Started: Do something...
ElseIf (e.ProgressPercentage = 100) Then
'Stopped: Do something...
End If
End Sub