This application demonstrates several useful techniques including:

• Loading and saving settings when the application starts and stops.
• Tracking multiple selected directories.
• Managing ListBox choices.
• Quickly listing the files in a directory with API functions.
• Converting long file names to short file names.
• Letting the user browse to select a directory.
• Randomizing an array.
• Generating a list of random files picked from the selected directories.
• Copying files.

When the program starts, it calls its LoadSettings routine. That routine uses GetSetting to loads saved settings. It loads source directory names and their selected state by looping through the setting values Source0, Source1, ... and Selected0, Selected1, ...

Private Sub LoadSettings()
    txtDestination.Text = GetSetting(APP_NAME, _
        "Settings", "DestinationDirectory", CurDir)
    txtNumFiles.Text = GetSetting(APP_NAME, _
        "Settings", "NumFiles", "1")

    lstSources.Items.Clear()
    Dim txt As String
    Dim new_index As Integer
    Dim is_selected As Boolean
    For i As Integer = 0 To 100
        txt = GetSetting(APP_NAME, "Settings", "Source" & _
            Format$(i), "")
        If Len(txt) < 1 Then Exit For
        new_index = lstSources.Items.Add(txt)
        is_selected = CBool(GetSetting(APP_NAME, _
            "Settings", "Selected" & Format$(i), "False"))
        lstSources.SetSelected(new_index, is_selected)
    Next i
End Sub

Next the program uses SaveSetting to save the current settings.

Private Sub SaveSettings()
    On Error Resume Next
    DeleteSetting(APP_NAME)
    On Error GoTo 0
    SaveSetting(APP_NAME, "Settings", _
        "DestinationDirectory", txtDestination.Text)
    SaveSetting(APP_NAME, "Settings", "NumFiles", _
        txtNumFiles.Text)

    For i As Integer = 0 To lstSources.Items.Count - 1
        SaveSetting(APP_NAME, "Settings", "Source" & _
            Format$(i), lstSources.Items(i).ToString)
        SaveSetting(APP_NAME, "Settings", "Selected" & _
            Format$(i), lstSources.GetSelected(i).ToString)
    Next i
End Sub

The main form checks the dialog's txtDir text box to see if the user made a selection. If txtDir is not blank, then the program uses ChDir to try to move to that directory. If it succeeds, the program adds the directory to the source list.

Private Sub btnAdd_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles btnAdd.Click
    Dim dlg As New dlgPickFolder
    dlg.txtDir.Text = CurDir()
    CenterFormOnForm(dlg, Me)
    dlg.ShowDialog(Me)

    If Len(dlg.txtDir.Text) > 0 Then
        On Error Resume Next
        ChDir(dlg.txtDir.Text)
        If Err.Number <> 0 Then
            MessageBox.Show("Error moving to directory '" & _
                _
                dlg.txtDir.Text & "'", _
                "Directory Error", _
                MessageBoxButtons.OK, _
                MessageBoxIcon.Error)
        Else
            lstSources.Items.Add(dlg.txtDir.Text)
        End If
        On Error GoTo 0
    End If
    dlg.Close()
End Sub

Public Sub CenterFormOnForm(ByVal frm_above As Form, ByVal _
    frm_below As Form)
    Dim working_area As Rectangle = _
        Screen.GetWorkingArea(New Point(0, 0))

    Dim x As Integer
    x = (frm_below.Left + frm_below.Right - _
        frm_above.Width) \ 2
    If x < 0 Then x = 0
    If x + frm_above.Width > working_area.Right Then
        x = working_area.Right - frm_above.Width
    End If

    Dim y As Integer
    y = (frm_below.Top + frm_below.Bottom - _
        frm_above.Height) \ 2
    If y < 0 Then y = 0
    If y + frm_above.Height > working_area.Bottom Then
        y = working_area.Bottom - frm_above.Height
    End If

    frm_above.SetBounds(x, y, frm_above.Width, _
        frm_above.Height)
End Sub

Private Sub btnRemove_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles btnRemove.Click
    If lstSources.Items.Count < 1 Then
        MessageBox.Show("No sources selected to delete", _
            "No Sources Selected", MessageBoxButtons.OK, _
            MessageBoxIcon.Information)
    ElseIf MessageBox.Show("Delete selected sources?", _
        "Delete Sources?", MessageBoxButtons.YesNo, _
        MessageBoxIcon.Question) = vbYes Then
        For Each source As Object In _
            lstSources.SelectedItems
            lstSources.Items.Remove(source)
        Next source
    End If
End Sub

Private Sub btnBrowse_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles btnBrowse.Click
    dlgFolder.SelectedPath = CurDir()
    If dlgFolder.ShowDialog(Me) = DialogResult.OK Then
        txtDestination.Text = dlgFolder.SelectedPath
        ChDir(dlgFolder.SelectedPath)
    End If
End Sub

It then makes an array containing the indexes of the files and uss subroutine RandomizeArray to randomize the indexes. Next it uses the indexes to access the files in random order and copies them to the destination directory.

Private Sub btnLoadFiles_Click(ByVal sender As _
    System.Object, ByVal e As System.EventArgs) Handles _
    btnLoadFiles.Click
    Dim file_names As Collection
    Dim num_files As Integer
    Dim indexes() As Integer
    Dim dest_dir As String
    Dim files_to_copy As Integer

    ' Make a list of all of the files.
    file_names = New Collection
    For Each source As String In lstSources.SelectedItems
        ListFiles(source, file_names)
    Next source

    ' See how many files we found.
    num_files = file_names.Count
    If num_files < 1 Then
        MessageBox.Show("No files found", "No Files", _
            MessageBoxButtons.OK, _
            MessageBoxIcon.Exclamation)
        Exit Sub
    End If

    ' Make the indexes array.
    ReDim indexes(num_files - 1)
    For i As Integer = 0 To num_files - 1
        indexes(i) = i + 1
    Next i

    ' Randomize the indexes array.
    RandomizeArray(indexes)

    ' Grab the first files.
    files_to_copy = CInt(txtNumFiles.Text)
    If files_to_copy > num_files Then files_to_copy = _
        num_files

    ' Start copying files.
    Me.Cursor = Cursors.WaitCursor
    Application.DoEvents()

    dest_dir = txtDestination.Text
    Dim file_name, file_title As String
    Dim files_copied As Integer = 0
    On Error Resume Next
    For i As Integer = 0 To files_to_copy - 1
        Me.Text = APP_NAME & " (" & i + 1 & ")"
        Me.Refresh()

        file_name = DirectCast(file_names(indexes(i)), _
            String)
        file_title = _
            file_name.Substring(file_name.LastIndexOf("\"))

        FileCopy(file_name, dest_dir & file_title)
        If Err.Number <> 0 Then
            MessageBox.Show("Error copying file '" & _
                file_name & "' to '" & _
                dest_dir & file_title & "'" & vbCrLf & _
                Err.Description, _
                "Copy Error", _
                MessageBoxButtons.OK, MessageBoxIcon.Error)
            Exit For
        End If

        files_copied += 1
        'Debug.WriteLine(i & ": FileCopy """ & _
        '    file_name & """, """ & _
        '    dest_dir & file_title & """")
    Next i
    On Error GoTo 0

    Me.Text = APP_NAME
    Me.Cursor = Cursors.Default

    MessageBox.Show("Copied " & files_copied & " files", _
        "Done", MessageBoxButtons.OK, _
        MessageBoxIcon.Information)
End Sub

Public Sub ListFiles(ByVal start_dir As String, ByVal _
    file_names As Collection)
    Dim new_files As String() = _
        Directory.GetFiles(start_dir, "*.mp3")
    For Each file_name As String In new_files
        file_names.Add(file_name)
    Next file_name
End Sub

' Randomize an array of integers indexed from 0.
Public Sub RandomizeArray(ByVal indexes() As Integer)
    Dim num_items As Integer
    Dim j As Integer
    Dim tmp As Integer

    ' Randomize the array.
    Randomize()
    num_items = indexes.GetUpperBound(0)
    For i As Integer = 0 To num_items - 2
        ' Pick a random entry.
        j = CInt(Int((num_items - i) * Rnd() + i))

        ' Swap the numbers.
        tmp = indexes(i)
        indexes(i) = indexes(j)
        indexes(j) = tmp
    Next i
End Sub