Visual Basic : Sélectionner une ligne dans une TextBox

#Region "Using Proxy"
    <Runtime.InteropServices.DllImport("wininet.dll", SetLastError:=True)> _
    Private Shared Function InternetSetOption(ByVal hInternet As IntPtr, ByVal dwOption As Integer, ByVal lpBuffer As IntPtr, ByVal lpdwBufferLength As Integer) As Boolean
    End Function

    Public Structure Struct_INTERNET_PROXY_INFO
        Public dwAccessType As Integer
        Public proxy As IntPtr
        Public proxyBypass As IntPtr
    End Structure

    Private Sub UseProxy(ByVal strProxy As String)
        Const INTERNET_OPTION_PROXY As Integer = 38
        Const INTERNET_OPEN_TYPE_PROXY As Integer = 3

        Dim struct_IPI As Struct_INTERNET_PROXY_INFO

        struct_IPI.dwAccessType = INTERNET_OPEN_TYPE_PROXY
        struct_IPI.proxy = Marshal.StringToHGlobalAnsi(strProxy)
        struct_IPI.proxyBypass = Marshal.StringToHGlobalAnsi("local")

        Dim intptrStruct As IntPtr = Marshal.AllocCoTaskMem(Marshal.SizeOf(struct_IPI))

        Marshal.StructureToPtr(struct_IPI, intptrStruct, True)

        Dim iReturn As Boolean = InternetSetOption(IntPtr.Zero, INTERNET_OPTION_PROXY, intptrStruct, System.Runtime.InteropServices.Marshal.SizeOf(struct_IPI))
    End Sub
#End Region

If Not TextBox1.Text = "" Then
            If CheckBox1.Checked = True Then
                If TextBox2.Text = "" Then
                    Dim info = New System.Media.SoundPlayer(My.Resources.info)
                    info.Play()
                    MsgBox("Veuillez choisir une liste de proxys valide !", MsgBoxStyle.Information, "Liste de proxys invalides")
                End If
                If Not TextBox2.Text = "" Then
                    Dim separateurs() As String = {vbCrLf, vbLf} 'Les caractères de reour à la ligne
                    Dim lignes() As String = TextBox2.Text.Split(separateurs, StringSplitOptions.None)

                    Dim hasard As System.Random = New System.Random()
                    Dim selection As String = lignes(hasard.Next(0, lignes.Length))
                    UseProxy(lignes(hasard.Next(0, lignes.Length)))
                    WebBrowser1.Navigate("monip.org")
                End If
            End If
        End If