WPF asynchronous invoke question

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