Background Cancle Event Form Closing Error - vb.net

Question

I have a background event that is consistently withdraws data. When I close the form background event doesn't cancel for some reason. If I enable a message in between it does...... I tried to put a time pause, REFRESH, and both. But its only works properly after the message box. I don't really understand why, since button it self to cancel works fine when form is not close. ERROR "Cannot access a disposed object.Object name: 'Form1'." Somehow it doesn't see "False" on closing.
Thanks!
Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
RED(False)
'Some other functions - WORK OK
End Sub
Private Sub RED(ByVal reads As Boolean)
bck.WorkerSupportsCancellation = True
If reads = True Then
bck.RunWorkerAsync()
ElseIf reads = False Then
bck.CancelAsync()
bck.Dispose()
End If
End Sub
Private Sub bck_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bck.DoWork
Do
If bck.CancellationPending = True Then --- DOESN'T look like see this without Message BOX
Exit Sub
End If
Me.Invoke(Sub()
'EVENT HERE WERE I AM GETTING AN ERROR --- HOWEVER, Works as a button when called on RED(False) and Works if I put a message BOX
End Sub)
Loop
End Sub

Answer 1

It would appear to be a matter of timing, as is often the case with multiple threads. What I would suggest is that, if the form is closed when the background task is in progress, you cancel the background task and then cancel the close. You can then close again when the background task has completed, e.g.
Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Do
If BackgroundWorker1.CancellationPending Then
'Cancel the background work.
Exit Do
End If
'Do the background work.
'...
Loop
End Sub
Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
'Close the form.
Close()
End Sub
Private Sub Form1_FormClosing(sender As Object, e As FormClosingEventArgs) Handles Me.FormClosing
If BackgroundWorker1.IsBusy Then
'Cancel the background task.
BackgroundWorker1.CancelAsync()
'Do not close the form this time.
e.Cancel = True
End If
End Sub
If you won't always want to close the form when the background task completes then you can indicate that to the RunWorkerCompleted event handler by, for instance, setting e.Result in the DoWork event handler and then testing it in the RunWorkerCompleted event handler, e.g.
Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
e.Result = False
Do
If BackgroundWorker1.CancellationPending Then
e.Result = True
'Cancel the background work.
Exit Do
End If
'Do the background work.
'...
Loop
End Sub
Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
If CBool(e.Result) Then
'Close the form.
Close()
End If
End Sub

Answer 2

Use PROGRESS REPORT instead of Invoke.
Private Sub bck_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bck.DoWork
Do
If bck.CancellationPending = True Then
Exit Sub
End If
bck.ReportProgress("WHATEVER YOU CAPTURING/VALUES UPDATE")
Loop
End Sub
Private Sub bck_dProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles bck.ProgressChanged
YOUR DISPLAY = ("WHATEVER YOU CAPTURING/VALUES UPDATE")
End Sub