Backgroundworker Errors - vb.net

Question

I am trying to implement BackgroundWorker in my vb.net code. I understand you cannot update the UI from the background worker. Since when setting breakpoints in my code in the Backgroundworker.DoWork sub I would get
Me.Accessibility.Object threw an exception of type 'System.InvalidOperationException'
Message "Cross-thread operation not valid: Control 'FrmLoad' accessed from a thread other than the thread it was created on."
To try to understand why this was happening I copied the code EXACTLY from
https://learn.microsoft.com/en-us/dotnet/api/system.componentmodel.backgroundworker?view=netframework-4.7.2
and when setting a breakpoints again in the DoWork sub I get the same exception. I have tried several other microsoft code examples with the same issue. Is there something wrong with the code?
Imports System
Imports System.ComponentModel
Imports System.Windows.Forms
Namespace BackgroundWorkerSimple
Public Partial Class Form1
Inherits Form
Public Sub New()
InitializeComponent()
backgroundWorker1.WorkerReportsProgress = True
backgroundWorker1.WorkerSupportsCancellation = True
End Sub
Private Sub startAsyncButton_Click(ByVal sender As Object, ByVal e As EventArgs)
If backgroundWorker1.IsBusy <> True Then
backgroundWorker1.RunWorkerAsync()
End If
End Sub
Private Sub cancelAsyncButton_Click(ByVal sender As Object, ByVal e As EventArgs)
If backgroundWorker1.WorkerSupportsCancellation = True Then
backgroundWorker1.CancelAsync()
End If
End Sub
Private Sub backgroundWorker1_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
Dim worker As BackgroundWorker = TryCast(sender, BackgroundWorker)
For i As Integer = 1 To 10
If worker.CancellationPending = True Then
e.Cancel = True
Exit For
Else
System.Threading.Thread.Sleep(500)
worker.ReportProgress(i * 10)
End If
Next
End Sub
Private Sub backgroundWorker1_ProgressChanged(ByVal sender As Object, ByVal e As ProgressChangedEventArgs)
resultLabel.Text = (e.ProgressPercentage.ToString() & "%")
End Sub
Private Sub backgroundWorker1_RunWorkerCompleted(ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs)
If e.Cancelled = True Then
resultLabel.Text = "Canceled!"
ElseIf e.[Error] IsNot Nothing Then
resultLabel.Text = "Error: " & e.[Error].Message
Else
resultLabel.Text = "Done!"
End If
End Sub
End Class
End Namespace
It's not actually hindering the code from running, but I want to make sure that the thread is actually remaining safe.

Answer 1

That sample code is written in C#, and you apparently left out a function and it’s call:
// Set up the BackgroundWorker object by
// attaching event handlers.
private void InitializeBackgroundWorker()
{
backgroundWorker1.DoWork +=
new DoWorkEventHandler(backgroundWorker1_DoWork);
backgroundWorker1.RunWorkerCompleted +=
new RunWorkerCompletedEventHandler(
backgroundWorker1_RunWorkerCompleted);
backgroundWorker1.ProgressChanged +=
new ProgressChangedEventHandler(
backgroundWorker1_ProgressChanged);
}
While this can be rewritten using addhandler, the vbish way to do this is to add a handles clause to you method declaration.

Answer 2

I believe this is what you are looking for:
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
InitializeComponent()
BackgroundWorker1.WorkerReportsProgress = True
BackgroundWorker1.WorkerSupportsCancellation = True
End Sub
Private Sub startAsyncButton_Click(sender As Object, e As EventArgs) Handles btn_Start.Click
If Not BackgroundWorker1.IsBusy Then
BackgroundWorker1.RunWorkerAsync()
End If
End Sub
Private Sub cancelAsyncButton_Click(sender As Object, e As EventArgs) Handles btn_Cancel.Click
If BackgroundWorker1.WorkerSupportsCancellation = True Then
BackgroundWorker1.CancelAsync()
End If
End Sub
Private Sub backgroundWorker1_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs) Handles BackgroundWorker1.DoWork
'Dim worker As BackgroundWorker = TryCast(sender, BackgroundWorker)
For i As Integer = 1 To 10
If Not BackgroundWorker1.CancellationPending Then
System.Threading.Thread.Sleep(500)
BackgroundWorker1.ReportProgress(i * 10)
Else
e.Cancel = True
Exit For
End If
Next
End Sub
Private Sub backgroundWorker1_ProgressChanged(ByVal sender As Object, ByVal e As ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
resultLabel.Text = (e.ProgressPercentage.ToString() & "%")
End Sub
Private Sub backgroundWorker1_RunWorkerCompleted(ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
If e.Cancelled = True Then
resultLabel.Text = "Canceled!"
ElseIf e.Error IsNot Nothing Then
resultLabel.Text = "Error: " & e.[Error].Message
Else
resultLabel.Text = "Done!"
End If
End Sub
The main thing it looked like you were missing was the Handles Event for the Background1.ProgressChanged