invalid cast exeption

Question

Hallo, ich möchte Messwerte aus einem Atmega chip per Uart in Visual Basic 2010 visualisieren. Das klappt auch ganz gut. Ich sehe am Bildschirm schöne Sinuskurven. Leider bekomme ich jedoch in unregelmäßigen Abständen eine Fehlermeldung. Invalid Cast exeption.  Ungültige Konvertierung von der Zeichenfolge  in Typ Integer.

z = SerialPort1.ReadLine
y(hh) = z

Ich habe bereits eine Konvertierung mittels Cint versucht aber ohne Erfolg. Bin für jede HIlfe dankbar. Gruß Holger (Code siehe unten)

Hi, i'm currently trying to visualize measured values in Visual basic using Uart. Everything is fine unless I receive an error message "Invalid Cast exeption" from time to time.

z = SerialPort1.ReadLine
y(hh) = z

I have already tried to convert the sting to int by using Cint. Unfortunately without success. Any help is appreciated. Many thanks Holger

Public Class Form1

  Public opx, upx, lpx, rpx, mypx, mxpx
  Dim hh As Integer
  Dim z As String
  Dim y(1000) As Integer


  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Try
      SerialPort1.PortName = "COM3"
      SerialPort1.BaudRate ="9600"
      SerialPort1.Open()
    Catch ex As Exception
      MsgBox("Verbindung fehlgeschlagen")
    End Try

  End Sub

  Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
    Dim l As Graphics = PictureBox1.CreateGraphics()

    If RadioButton1.Checked = True And hh < 500 Then
      hh = hh + 1
      z = SerialPort1.ReadLine
      y(hh) = z
      l.DrawLine(Pens.MidnightBlue, hh, y(hh - 1), hh + 1, y(hh))
    End If

  End Sub

  Private Sub RadioButton1_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RadioButton1.CheckedChanged

  End Sub

  Private Sub PictureBox1_Paint(ByVal sender As System.Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles PictureBox1.Paint
    Dim l As Graphics = e.Graphics 'Deklaration der Variable l als Grafik
    Dim opx = 0 'obenpixel
    Dim upx = PictureBox1.Height 'untenpixel
    Dim lpx = 0 'linkspixel
    Dim rpx = PictureBox1.Width 'rechtspixel
    Dim mxpx As Integer = PictureBox1.Width / 2 'Hälfte von der Breite (mx = x-Achse)
    Dim mypx As Integer = PictureBox1.Height / 2 'Hälfte von der Länge (my = y-Achse)

    l.DrawLine(Pens.Black, 0, opx, 0, upx) 'y-Achse
    l.DrawLine(Pens.PaleGreen, 0, mypx - 50, rpx, mypx - 50)
    l.DrawLine(Pens.PaleGreen, 0, mypx - 100, rpx, mypx - 100)
    l.DrawLine(Pens.PaleGreen, 0, mypx - 150, rpx, mypx - 150)
    l.DrawLine(Pens.PaleGreen, 0, mypx - 200, rpx, mypx - 200)
    l.DrawLine(Pens.PaleGreen, 0, mypx - 250, rpx, mypx - 250)
    l.DrawLine(Pens.Black, lpx, mypx, rpx, mypx) 'x-Achse
    l.DrawLine(Pens.PaleGreen, 0, mypx + 50, rpx, mypx + 50)
    l.DrawLine(Pens.PaleGreen, 0, mypx + 100, rpx, mypx + 100)
    l.DrawLine(Pens.PaleGreen, 0, mypx + 150, rpx, mypx + 150)
    l.DrawLine(Pens.PaleGreen, 0, mypx + 200, rpx, mypx + 200)
    l.DrawLine(Pens.PaleGreen, 0, mypx + 250, rpx, mypx + 250)

  End Sub
End Class