Notice to all .NET Experts who experience imagelist

''Begin Form1.vb
''===================
Public Class Form1
    'Inherits Form
    Private ThumbEntry() As ListViewItem
    Private stopwatch As New Stopwatch
    Private length As Integer
 
    Private nextdir As String = Nothing
    Private lastdir As String = "D:\All1000mixImages"
    Private retdir As String
 
    Private basePath As IO.DirectoryInfo
    Private DI As IO.DirectoryInfo
 
    Private cachesize As Integer = 0
    Private firstnext As Integer = 0
    Private nextfirst As Integer = 0
 
    Private filename As String
    Private fi As Object
 
    Private Imagelist1 As New ImageList
    Private Imagelist2 As New ImageList
 
    Dim imageStream As System.IO.Stream
    Private istream As ImageListStreamer
    Private h As New Hashtable()
 
    Private Sub ListView1_RetrieveVirtualItem(ByVal sender As Object, ByVal e As RetrieveVirtualItemEventArgs) Handles ListView1.RetrieveVirtualItem
        'Caching is not required but improves performance on large sets.
        'To leave out caching, don't connect the CacheVirtualItems event 
        'and make sure myCache is null.
        'check to see if the requested item is currently in the cache
        If Not (ThumbEntry Is Nothing) Then 'AndAlso e.ItemIndex >= cc AndAlso e.ItemIndex < cc + ThumbEntry.Length Then
            'A cache hit, so get the ListViewItem from the cache instead of making a new one.
            e.Item = ThumbEntry((e.ItemIndex))
 
        Else
            'A cache miss, so create a new ListViewItem and pass it back.
            'Dim x As Integer = 1
            'e.Item = New ListViewItem(x.ToString())
            e.Item = New ListViewItem()
            'ShowImages(lastdir)
        End If
    End Sub
 
    'Manages the cache.  ListView calls this when it might need a 
    'cache refresh.
    Private Sub ListView1_CacheVirtualItems(ByVal sender As Object, ByVal e As CacheVirtualItemsEventArgs) Handles ListView1.CacheVirtualItems
        'We've gotten a request to refresh the cache.
        'First check if it's really neccesary.
        If Not (ThumbEntry Is Nothing) Then 'AndAlso e.StartIndex >= cc AndAlso e.EndIndex <= cc + ThumbEntry.Length Then
            'If the newly requested cache is a subset of the old cache, 
            'no need to rebuild everything, so do nothing.
            Return
        Else
            'Now we need to rebuild the cache.
            'Fill the cache with the appropriate ListViewItems.
            ShowImages(lastdir)
        End If
 
    End Sub
 
    Private Function gti(ByVal filename As String, ByVal width As Integer, ByVal height As Integer) As Bitmap
        Using fs As New IO.FileStream(filename, IO.FileMode.Open, IO.FileAccess.Read)
            Using img As Image = Image.FromStream(fs, True, False)
                Return DirectCast(img.GetThumbnailImage(width, height, Nothing, IntPtr.Zero), Bitmap)
            End Using
        End Using
    End Function
 
    Private Sub ShowImages(ByVal filePath As String)
        Dim p As Integer = 0
        Dim q As Integer = 0
        basePath = New IO.DirectoryInfo(filePath)
        '--------------------
        stopwatch.Reset()
        stopwatch.Start()
        ThumbEntry = New ListViewItem(length) {}
 
        For Each filename In IO.Directory.GetFiles(filePath)
            fi = New IO.FileInfo(filename)
            If fi.Extension.toupper.Equals(".BMP") Or _
               fi.Extension.toupper.Equals(".JPG") Or _
               fi.Extension.toupper.Equals(".GIF") Then
                ThumbEntry(q) = New ListViewItem()
                ThumbEntry(q).Text = fi.Name
 
                h.Add(q, gti(fi.FullName, 100, 80))
 
                ThumbEntry(q).ImageIndex = Imagelist1.Images.Count - 1
 
                q += 1
            End If
            p = CInt(q / length * 100)
            ProgressBar1.Value = p
        Next filename
        ListView1.VirtualListSize = length
 
        stopwatch.Stop()
        Me.Text = "ListView in " + stopwatch.ElapsedMilliseconds.ToString + " mS"
        '-----------------
    End Sub
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'Imagelist1 = New ImageList
        'Imagelist2 = New ImageList
 
        Imagelist2.ColorDepth = ColorDepth.Depth16Bit
        Imagelist2.ImageSize = New Size(100, 80)
        ListView1.View = View.LargeIcon
        ListView1.LargeImageList = Imagelist2
 
        Imagelist1.ColorDepth = ColorDepth.Depth16Bit
        Imagelist1.ImageSize = New Size(100, 80)
        ListView1.View = View.LargeIcon
        ListView1.LargeImageList = Imagelist1
 
        Application.DoEvents()
        length = IO.Directory.GetFiles(lastdir, "*.jpg").Length
        length = length + IO.Directory.GetFiles(lastdir, "*.bmp").Length
        length = length + IO.Directory.GetFiles(lastdir, "*.gif").Length
        ListView1.VirtualListSize = length
 
        cachesize = 100
        firstnext = 0
    End Sub
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        '--------------------
        stopwatch.Reset()
        stopwatch.Start()
        'GC.Collect(256)
        'GC.AddMemoryPressure(256)
        'Imagelist2 = New ImageList
        ListView1.BeginUpdate()
If cachesize >= length Then cachesize = length - 1
        For i As Integer = firstnext To cachesize
            Imagelist1.Images.Add(h.Item(i))
            ThumbEntry(i).ImageIndex = Imagelist1.Images.Count - 1
        Next
        ListView1.EndUpdate()
        'GC.WaitForPendingFinalizers()
        'Imagelist1 = Imagelist2
 
        nextfirst = cachesize
        firstnext = nextfirst + 1
        nextfirst = 0
        cachesize = cachesize + 100
 
        stopwatch.Stop()
        Me.Text = "ImageList in " + stopwatch.ElapsedMilliseconds.ToString + " mS"
        '-----------------
    End Sub
 
    Private Sub InitializeComponent()
        Me.ListView1 = New System.Windows.Forms.ListView
        Me.ProgressBar1 = New System.Windows.Forms.ProgressBar
        Me.Button1 = New System.Windows.Forms.Button
        Me.SuspendLayout()
        '
        'ListView1
        '
        Me.ListView1.AutoArrange = False
        Me.ListView1.HeaderStyle = System.Windows.Forms.ColumnHeaderStyle.None
        Me.ListView1.ImeMode = System.Windows.Forms.ImeMode.Off
        Me.ListView1.Location = New System.Drawing.Point(12, 34)
        Me.ListView1.Name = "ListView1"
        Me.ListView1.ShowGroups = False
        Me.ListView1.Size = New System.Drawing.Size(508, 598)
        Me.ListView1.TabIndex = 0
        Me.ListView1.UseCompatibleStateImageBehavior = False
        Me.ListView1.VirtualMode = True
        '
        'ProgressBar1
        '
        Me.ProgressBar1.Location = New System.Drawing.Point(12, 5)
        Me.ProgressBar1.Name = "ProgressBar1"
        Me.ProgressBar1.Size = New System.Drawing.Size(431, 23)
        Me.ProgressBar1.TabIndex = 3
        '
        'Button1
        '
        Me.Button1.Location = New System.Drawing.Point(449, 5)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(75, 23)
        Me.Button1.TabIndex = 9
        Me.Button1.Text = "Button1"
        Me.Button1.UseVisualStyleBackColor = True
        '
        'Form1
        '
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 13.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(536, 658)
        Me.Controls.Add(Me.Button1)
        Me.Controls.Add(Me.ProgressBar1)
        Me.Controls.Add(Me.ListView1)
        Me.Name = "Form1"
        Me.Text = "Form111b"
        Me.WindowState = System.Windows.Forms.FormWindowState.Maximized
        Me.ResumeLayout(False)
 
    End Sub
 
End Class
''End Form1.vb
''===================
 
 
''--------------------------
''Begin Form1.Designer.vb
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Partial Class Form1
    Inherits System.Windows.Forms.Form
  
    Friend WithEvents ListView1 As System.Windows.Forms.ListView
    Friend WithEvents ProgressBar1 As System.Windows.Forms.ProgressBar
    Friend WithEvents Button1 As System.Windows.Forms.Button
 
End Class
''End Form1.Designer.vb
''-----------------------------

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