Public Class Form1
    Dim PictureList As New List(Of String)(IO.Directory.GetFiles("C:\Dokumente" & _
      "und Einstellungen\Cath\Eigene Dateien\Eigene Bilder\testbilder\"))
    Dim PictureIndex As Integer = 0
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
 
    End Sub
    Public Sub New()
        Me.InitializeComponent()
        LoadImage()
    End Sub
    Sub LoadImage()
        Me.picMain.Image = New Bitmap(PictureList.Item(PictureIndex))
        LoadThumbnails()
    End Sub
    Sub LoadThumbnails()
        'Erstes Thumbnail
        If PictureIndex > 1 Then
            Me.picThumb1.Image = New Bitmap(PictureList.Item(PictureIndex - 2))
        Else
            If PictureIndex = 0 Then
                Me.picThumb1.Image = New Bitmap(PictureList.Item( _
                  PictureList.Count - 2))
            ElseIf PictureIndex = 1 Then
                Me.picThumb1.Image = New Bitmap(PictureList.Item( _
                  PictureList.Count - 1))
            End If
        End If
 
        'Zweites Thumbnail
        If PictureIndex > 0 Then
            Me.picThumb2.Image = New Bitmap(PictureList.Item(PictureIndex - 1))
        Else
 
            Me.picThumb2.Image = New Bitmap(PictureList.Item(PictureList.Count _
              - 1))
        End If
        'Drittes Thumbnail
        Me.picThumb3.Image = New Bitmap(PictureList.Item(PictureIndex))
 
        'Viertes Thumbnail
        If PictureList.Count > PictureIndex + 1 Then
            Me.picThumb4.Image = New Bitmap(PictureList.Item(PictureIndex + 1))
        Else
            Me.picThumb4.Image = New Bitmap(PictureList.Item(0))
        End If
 
        'Fünftes Thumbnail
        If PictureList.Count > PictureIndex + 2 Then
            Me.picThumb5.Image = New Bitmap(PictureList.Item(PictureIndex + 2))
        Else
            If PictureIndex = PictureList.Count - 2 Then
                Me.picThumb5.Image = New Bitmap(PictureList.Item(0))
            ElseIf PictureIndex = PictureList.Count - 1 Then
                Me.picThumb5.Image = New Bitmap(PictureList.Item(1))
            End If
        End If
    End Sub
    Private Sub butPrevious_Click_1(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles butPrevious.Click
        If PictureIndex = 0 Then
            PictureIndex = PictureList.Count - 1
            MessageBox.Show(PictureIndex)
        Else
            PictureIndex -= 1
        End If
 
        LoadImage()
    End Sub
    Private Sub butNext_Click_1(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles butNext.Click
        If PictureIndex = PictureList.Count - 1 Then
            PictureIndex = 0
        Else
            PictureIndex += 1
        End If
        LoadImage()
    End Sub
End Class