Imports System.IO
Imports System
Imports Microsoft.VisualBasic
 
Public Class Form1
    Dim sLines() As String
    Public Function ReadLine(ByVal sFile As String, _
  Optional ByVal nLine As Long = 1) As String
 
        Dim oFSO As Object
        Dim oFile As Object
 
        On Error GoTo ErrHandler
 
        oFSO = CreateObject("Scripting.FileSystemObject")
 
        If oFSO.FileExists(sFile) Then
            oFile = oFSO.OpenTextFile(sFile)
 
            sLines = Split(oFile.ReadAll, vbCrLf)
 
            oFile.Close()
 
            Select Case Math.Sign(nLine)
                Case 1
                    ReadLine = sLines(nLine - 1)
 
                Case -1
                    ReadLine = sLines(UBound(sLines) + nLine + 1)
            End Select
        End If
 
ErrHandler:
        oFile = Nothing
        oFSO = Nothing
    End Function
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
 
        ProgressBar1.Value = 0
        Dim wert() As String
        Dim wert2 As Object
 
        ComboBox1.Items.Clear()
 
        For a = 1 To 40000
            ProgressBar1.Value = a
            wert = Split(ReadLine("C:\Test.txt", a), ";")
            wert2 = wert(1)
            wert = wert
            ComboBox1.Items.Add(wert2)
        Next a
 
    End Sub
 
    Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, _
      ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
 
        ProgressBar1.Value = 0
        Dim wert() As String
        Dim wert2 As Object
        Dim wert3 As Object
 
        ComboBox2.Items.Clear()
 
        For a = 1 To 40000
            ProgressBar1.Value = a
            wert = Split(ReadLine("C:\Test.txt", a), ";")
            wert2 = wert(1)
            If wert2 = ComboBox1.Text Then
                wert3 = wert(2)
                ComboBox2.Items.Add(wert3)
            End If
        Next a
 
    End Sub