Public Class Form1
  Inherits System.Windows.Forms.Form

Vom Windows Form Designer generierter Code

  Private sFile As String = System.IO.Path.Combine _
        (Application.StartupPath, "Liste.dat")

  Private Sub SaveListbox(ByVal ListBox As ListBox, _
        ByVal sFile As String)

    Dim writer As IO.StreamWriter
    Dim i As Short

    writer = New IO.StreamWriter(sFile)

    For Each item As Object In ListBox1.Items
      writer.WriteLine(ListBox.Items(i))
      i += 1
    Next

    writer.Close()
  End Sub

  Private Sub ReadListbox(ByVal ListBox As ListBox, _
        ByVal sFile As String)

    Dim reader As IO.StreamReader
    Dim sLine As String

    ListBox.Items.Clear()

    Dim oFile As New IO.FileInfo(sFile)
    If oFile.Exists() = True Then
      reader = New IO.StreamReader(sFile)
      Do
        sLine = reader.ReadLine()
        If IsNothing(sLine) Then Exit Do
        ListBox.Items.Add(sLine)
      Loop
      reader.Close()
    End If
  End Sub

  Private Sub Form1_Load(ByVal sender As System.Object, _
         ByVal e As System.EventArgs) Handles MyBase.Load
    With ListBox1
      .Items.Add("Arnie Müller")
      .Items.Add("Peter Pankrat")
      .Items.Add("Annelise Netrowic")
    End With
  End Sub

  Private Sub Button1_Click(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles Button1.Click
    SaveListbox(ListBox1, sFile)
  End Sub

  Private Sub Button2_Click(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles Button2.Click
    ReadListbox(ListBox1, sFile)
  End Sub

  Private Sub MenuItem1_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles MenuItem1.Click

    If ListBox1.SelectedIndex() <> -1 Then
      ListBox1.Items.RemoveAt(ListBox1.SelectedIndex())
    Else
      MessageBox.Show("Bitte den zu löschenden Eintrag " & _
            zuerst markieren!", "Eintrag markieren", _
            MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
    End If

  End Sub
End Class

Public Class Form1
  ' Der Speicherort der Textdatei
  Private FILENAME As String = IO.Path.Combine _
          (Application.StartupPath, "Liste.dat")

  Private Sub SaveListbox(ByVal ListBox As ListBox, _
          ByVal sFile As String)
    ' Inhalt einer ListBox speichern
    With ListBox1.Items
      ' Alle Inhalte aus ListBox ins Stringarray bringen
      Dim strArr(.Count - 1) As String
      .CopyTo(strArr, 0)

      ' Array In Textdatei speichern
      IO.File.WriteAllLines(sFile, strArr)
    End With
  End Sub

  Private Sub ReadListbox(ByVal ListBox As ListBox, _
          ByVal sFile As String)
    ' Vorhandenen ListBox-Inhalt löschen
    ListBox.Items.Clear()

    ' Existsiert die Datei?
    If IO.File.Exists(sFile) = True Then
      ' Inhalt einer Datei in ListBox einlesen
      Dim strArr() As String = IO.File.ReadAllLines(sFile)
      ListBox.Items.AddRange(strArr)
    End If
  End Sub

  Private Sub Form1_Load(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles MyBase.Load
    ' ListBox beim Anwendungstart füllen
    Dim strPersonen() As String = {"Arnie Müller", "Peter Pankrat",_
        "Annelise Netrowic"}
    ListBox1.Items.AddRange(strPersonen)
  End Sub

  Private Sub Button1_Click(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles Button1.Click
    ' ListBox speichern
    SaveListbox(ListBox1, FILENAME)
  End Sub

  Private Sub Button2_Click(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles Button2.Click
    ' ListBox einlesen
    ReadListbox(ListBox1, FILENAME)
  End Sub

  Private Sub Button3_Click(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles Button3.Click
    ' Inhalt der Listbox löschen
    ListBox1.Items.Clear()
  End Sub

  Private Sub Button4_Click(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles Button4.Click
    If CheckBox1.Checked Then
      ' Doppeleinträge verhindern (Contains)
      If Not ListBox1.Items.Contains(TextBox1.Text) Then
        ' Eintrag hinzufügen
        ListBox1.Items.Add(TextBox1.Text)
      Else
        MessageBox.Show("Eintrag schon vorhanden!", _
            "Doppeleinträge werden nicht zugelassen.", _
            MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
      End If
    Else
      ' Eintrag hinzufügen (Doppelte zulassen)
      ListBox1.Items.Add(TextBox1.Text)
    End If
  End Sub

  Private Sub Button5_Click(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles Button5.Click
    ' Applikation beenden
    Me.Close()
  End Sub

  Private Sub MarkiertenEintragLöschenToolStripMenuItem_Click(ByVal _
          sender As System.Object, ByVal e As System.EventArgs) _
          Handles MarkiertenEintragLöschenToolStripMenuItem.Click
    ' Markierten Eintrag in Listbox löschen
    ' über das Contextmenu (rechte Maustaste)
    If ListBox1.SelectedIndex() <> -1 Then
      ListBox1.Items.RemoveAt(ListBox1.SelectedIndex())
    Else
      MessageBox.Show("Bitte den zu löschenden Eintrag zuerst"_
             "markieren!", "Eintrag markieren", _
             MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
    End If
  End Sub
End Class