Cannot Await BackgroundWorker CancelAsync - vb.net

Question

I have a BackgroundWorker in my project that I want to restart in a single method. However, when I use the CancelAsync() method and then the RunWorkerAsync() method immediately after, the cancel hasn't completed and 2 instances of the BackgroundWorker are started and an InvalidOperationException is thrown. To combat this, I made the method async (it's a Sub method) and awaited the CancelAsync() to wait for it to finish. However, this returns an error that the expression doesn't produce a value. Is this due to the calling or the worker's method?
Worker Method:
Private Sub GIFworker(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles bkwGIF.DoWork
Dim hum As Integer = e.Argument
If hum Mod 2 = 1 Then
While bkwGIF.CancellationPending = False
pbxRpsHum.Image = ilRPS.Images(0)
Thread.Sleep(1000)
pbxRpsHum.Image = ilRPS.Images(1)
Thread.Sleep(1000)
End While
Else
While bkwGIF.CancellationPending = False
pbxRpsHum.Image = ilRPS.Images(0)
Thread.Sleep(1000)
pbxRpsHum.Image = ilRPS.Images(3)
Thread.Sleep(1000)
End While
End If
End Sub
Calling CancelAsync() (hum is an integer):
Await bkwGIF.CancelAsync()
bkwGIF.RunWorkerAsync(hum)

Answer 1

Here's an example of how you cancel a BackgroundWorker:
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
'Raise the DoWork event in a worker thread.
Me.BackgroundWorker1.RunWorkerAsync()
End Sub
'This method is executed in a worker thread.
Private Sub BackgroundWorker1_DoWork(sender As Object, e As DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Dim worker As BackgroundWorker = DirectCast(sender, BackgroundWorker)
For i As Integer = 1 To 100
If worker.CancellationPending Then
'The user has cancelled the background operation.
e.Cancel = True
Exit For
End If
'Raise the ProgressChanged event in the UI thread.
worker.ReportProgress(i, i & " iterations complete")
'Perform some time-consuming operation here.
Threading.Thread.Sleep(250)
Next i
End Sub
'This method is executed in the UI thread.
Private Sub BackgroundWorker1_ProgressChanged(sender As Object, e As ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
Me.ProgressBar1.Value = e.ProgressPercentage
Me.Label1.Text = TryCast(e.UserState, String)
End Sub
'This method is executed in the UI thread.
Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
If e.Cancelled Then
'The background operation was cancelled.
Me.Label1.Text = "Operation cancelled"
Else
'The background operation completed normally.
Me.Label1.Text = "Operation complete"
End If
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
'Only cancel the background opertion if there is a background operation in progress.
If Me.BackgroundWorker1.IsBusy Then
Me.BackgroundWorker1.CancelAsync()
End If
End Sub
If you want to restart the background work on a cancellation then you would do so in the RunWorkerCompleted event handler when you detect that e.Cancelled is True.