Public Enum RandomTextType
        LowerCaseLetters = 1
        UpperCaseLetters = 2
        LowerCaseLettersMixedNumbers = 3
        UpperCaseLettersMixedNumbers = 4
        MixedAll = 5
    End Enum

 ''' <summary>
    '''   Erzeugen von Zufallsstring
    ''' </summary>
    ''' <param name="theLen">die Länge des Strings</param>
    ''' <param name="art">die Art der Zusammensetzung des Strings</param>
    Public Function CreateRandomString(theLen As Short, art As RandomTextType) _
      As String
        Const lowerChars = "abcdefghijklmnopqrstuvwxyzäöüß"
        Const upperChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZÄÖÜ"
        Const numericChars = "0123456789"
        Const specChars = "!§$%&/()=?{[]}+*~#'-_.:,;<>"
 
        Dim rs As String = ""
        Dim ast As String = "", le, ix As Short
        Dim rnd As New Random()
 
        ' Zusammensetzung gemäß vorgegebener Art
        Select Case art
            Case RandomTextType.LowerCaseLetters
                ast = lowerChars
            Case RandomTextType.UpperCaseLetters
                ast = upperChars
            Case RandomTextType.LowerCaseLettersMixedNumbers
                ast = lowerChars + numericChars
            Case RandomTextType.UpperCaseLettersMixedNumbers
                ast = upperChars + numericChars
            Case RandomTextType.MixedAll
                ast = lowerChars + upperChars + numericChars + specChars
        End Select
 
        le = ast.Length - 1
        For i As Short = 1 To theLen
            ix = rnd.Next(0, le)
            rs += ast.Substring(ix, 1)
        Next
 
        ' Rückgabe des Strings
        Return rs
    End Function

Dim file As System.IO.StreamWriter
        file = My.Computer.FileSystem.OpenTextFileWriter("D:\pPA - praktische" & _
          "Pflegeausbildung\pPA\pPA\Kalender-Export.ics", False)
    file.WriteLine("BEGIN:VTIMEZONE")
        file.WriteLine("TZID:Europe/Berlin")
        file.WriteLine("X-LIC-Location:Europe/Berlin")
        file.WriteLine("BEGIN:DAYLIGHT")
        file.WriteLine("TZOFFSETFROM:+0100")
        file.WriteLine("TZOFFSETTO:+0200")
        file.WriteLine("TZNAME:CEST")
        file.WriteLine("DTSTART:19700329T020000")
        file.WriteLine("RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3")
        file.WriteLine("End:DAYLIGHT")
        file.WriteLine("BEGIN:STANDARD")
        file.WriteLine("TZOFFSETFROM:+0200")
        file.WriteLine("TZOFFSETTO:+0100")
        file.WriteLine("TZNAME:CET")
        file.WriteLine("DTSTART:19701025T030000")
        file.WriteLine("RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10")
        file.WriteLine("End:STANDARD")
        file.WriteLine("End:VTIMEZONE")
    For x As Integer = 0 To 20
              Dim Zufallszahl As String = CreateRandomString(100, _
                RandomTextType.MixedAll)
file.WriteLine("UID:" & Zufallszahl)
next

 For x As Integer = 0 To 20
              Dim Zufallszahl As String = CreateRandomString(100, _
                RandomTextType.MixedAll)
MsgBox(Zufallszahl)
file.WriteLine("UID:" & Zufallszahl)
next

  Dim rnd As New Random(Now.Millisecond)
 
  Public Function CreateRandomString(theLen As Short, art As RandomTextType) As _
    String
        Const lowerChars As String = "abcdefghijklmnopqrstuvwxyzäöüß"
        Const upperChars As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZÄÖÜ"
        Const numericChars As String = "0123456789"
        Const specChars As String = "!§$%&/()=?{[]}+*~#'-_.:,;<>"
 
        Dim rs As String = ""
        Dim ast As String = "", le, ix As Integer
 
        ' Zusammensetzung gemäß vorgegebener Art
        Select Case art
            Case RandomTextType.LowerCaseLetters
                ast = lowerChars
            Case RandomTextType.UpperCaseLetters
                ast = upperChars
            Case RandomTextType.LowerCaseLettersMixedNumbers
                ast = lowerChars + numericChars
            Case RandomTextType.UpperCaseLettersMixedNumbers
                ast = upperChars + numericChars
            Case RandomTextType.MixedAll
                ast = lowerChars + upperChars + numericChars + specChars
        End Select
 
        le = ast.Length - 1
        For i As Short = 1 To theLen
            ix = rnd.Next(0, le + 1)
            rs &= ast.Substring(ix, 1)
        Next
 
        ' Rückgabe des Strings
        Return rs
  End Function