WPF asynchronous invoke question - wpf

Question

What's wrong in my code? It's not updating the TextBox and the ProgressBar while deleting files.
Imports System.Windows.Threading
Imports System.IO
Class MainWindow
Private Sub bt_Click(ByVal sender As Object,
ByVal e As RoutedEventArgs) Handles bt.Click
Dim sb As New System.Text.StringBuilder
Dim files = IO.Directory.EnumerateFiles(
My.Computer.FileSystem.SpecialDirectories.Temp, "*.*",
SearchOption.TopDirectoryOnly)
Dim count = files.Count
pb.Minimum = 0
pb.Maximum = count
For i = 0 To count - 1
Dim f = files(i)
Dispatcher.BeginInvoke(
New Action(Of String, Integer)(
Sub(str, int)
tb.SetValue(TextBox.TextProperty, str)
pb.SetValue(ProgressBar.ValueProperty, int)
End Sub),
DispatcherPriority.Send,
f, i + 1)
Try
File.Delete(f)
Catch ex As Exception
sb.AppendLine(f)
End Try
Dim exceptions = sb.ToString
Stop
Next
End Sub
End Class

Answer 1

I got this working with the BackgroundWorker object. This places your work in a background thread, with calls to update the UI going through the ProgressChanged event. I also used Invoke instead of BeginInvoke within the work loop, which forces the loop to wait for the UI to become updated before it proceeds.
Imports System.ComponentModel
Imports System.IO
Class MainWindow
Private WithEvents bw As New BackgroundWorker
Private Sub Button1_Click(ByVal sender As System.Object,
ByVal e As RoutedEventArgs) Handles btn.Click
pb.Minimum = 0
pb.Maximum = 100
bw.WorkerReportsProgress = True
bw.RunWorkerAsync()
End Sub
Private Sub bw_DoWork(ByVal sender As Object,
ByVal e As DoWorkEventArgs) Handles bw.DoWork
Dim sb As New System.Text.StringBuilder
Dim files = IO.Directory.EnumerateFiles(
My.Computer.FileSystem.SpecialDirectories.Temp, "*.*",
SearchOption.TopDirectoryOnly)
Dim count = files.Count
Me.Dispatcher.BeginInvoke(Sub()
tb.Text = "SOMETHING ELSE"
End Sub)
For i = 0 To count - 1
Dim f = files(i)
Dim myI = i + 1
Me.Dispatcher.Invoke(
Sub()
bw.ReportProgress(CInt((myI / count) * 100), f)
End Sub)
'Try
' File.Delete(f)
'Catch ex As Exception
' sb.AppendLine(f)
'End Try
Dim exceptions = sb.ToString
'Stop
Next
End Sub
Private Sub bw_ProgressChanged(
ByVal sender As Object,
ByVal e As ProgressChangedEventArgs) Handles bw.ProgressChanged
Dim fString As String = TryCast(e.UserState, String)
Me.Dispatcher.BeginInvoke(Sub()
tb.Text = fString
End Sub)
End Sub
End Class