BackroundWorker Problem that I can't figure out

[Pradeep1210]

here's an example:

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        BackgroundWorker1.RunWorkerAsync()
    End Sub

    Private Sub BackgroundWorker1_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
        For x As Integer = 1 To 10
            setText(x.ToString)
            MsgBox(getText)
        Next
    End Sub

    Private Delegate Sub setTextCallBack(ByVal newValue As String)
    Private Sub setText(ByVal newValue As String)
        If TextBox1.InvokeRequired Then
            TextBox1.Invoke(New setTextCallBack(AddressOf setText), newValue)
        Else
            TextBox1.Text = newValue
        End If
    End Sub

    Private Delegate Function getTextCallBack() As String
    Private Function getText() As String
        If TextBox1.InvokeRequired Then
            Return DirectCast(TextBox1.Invoke(New getTextCallBack(AddressOf getText)), String)
        Else
            Return TextBox1.Text
        End If
    End Function

End Class

While this would work, this seems to defeat the whole purpose of the BackgroundWorker class. The background worker class was really meant to avoid this type of code. It has all the logic already built into it.
Whenever you want to access any UI element, do that via the ReportProgress method and ProgressChanged event. You can pass the ProgressPercentage to the ProgressReport method, telling it how much of your work is complete. Additionally you can pass it the UserState parameter with whatever value you want and do UI related things with that, if required. These two things are available for use in the ProgressChanged event handler.

Here is an example of how to do it the proper way, avoiding delegates:
Put a TextBox, a ProgressBar, and two Buttons on a form and the following code.

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    ProgressBar1.Maximum = 100
    ProgressBar1.Value = 0
    BackgroundWorker1.WorkerReportsProgress = True
    BackgroundWorker1.WorkerSupportsCancellation = True
    BackgroundWorker1.RunWorkerAsync()
End Sub
 
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
    ' Cancel button
    BackgroundWorker1.CancelAsync()
End Sub
 
Private Sub BackgroundWorker1_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
    Const MAX As Integer = 1000
    For i As Integer = 1 To MAX
        ' some delay to simulate work in progress
        Threading.Thread.Sleep(100)
 
        ' report the progress to UI. You can optionally pass any values required to be accessed by UI elements.
        Dim progress As Integer = (i * 100) \ MAX
        BackgroundWorker1.ReportProgress(progress, i)
        ' check if user wants to cancel this task. If Yes, then quit.
        If BackgroundWorker1.CancellationPending Then
            e.Cancel = True
            Exit Sub
        End If
    Next
End Sub
 
Private Sub BackgroundWorker1_ProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
    ProgressBar1.Value = e.ProgressPercentage
    TextBox1.Text = e.UserState.ToString
End Sub
 
Private Sub BackgroundWorker1_RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
    If e.Cancelled Then
        MessageBox.Show("Cancelled!")
    Else
        MessageBox.Show("Work done")
    End If
End Sub

Run the program and first click Button1. It will start the background worker thread. Click Button2 anywhere in between to cancel it.