Dim saved As Boolean = True
 
    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles TextBox1.TextChanged
        saved = False
    End Sub
 
    Private Sub Form1_Closing(ByVal sender As Object, ByVal e As _
      System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
        If Not saved Then
            Select Case MessageBox.Show("Änderungen speichern?", _
              Application.ProductName, MessageBoxButtons.YesNoCancel)
                Case DialogResult.Yes
                    ' Code zum Speichern
                Case DialogResult.Cancel
                    e.Cancel = True
            End Select
        End If
    End Sub