Using the BackgroundWorker Component

[jmcilhinney]

C# version here.

Create a new Windows Forms project. Add a Label, a ProgressBar and a BackgroundWorker to the form. Set the BackgroundWorker's WorkerReportsProgress property to True. Add the following code then run the project.

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.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(ByVal sender As Object, _
                                     ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
    Dim worker As System.ComponentModel.BackgroundWorker = DirectCast(sender, System.ComponentModel.BackgroundWorker)
 
    For i As Integer = 1 To 100
        '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(ByVal sender As Object, _
                                              ByVal e As System.ComponentModel.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(ByVal sender As Object, _
                                                 ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
    Me.Label1.Text = "Operation complete"
End Sub