using invoke in a class rather than in a form - vb.net

Question

i wrote a program reading a com port for a signal, everything was working fine, but they wanted to make the application a service so i swapped the application type to 'windows service' and created a class and put everything in the form in there and i called the class in my Main() in the startup module. the line,
Me.Invoke(New myDelegate(AddressOf UPdateVariable), New Object() {})
in the class has invoke in red saying that, "'Invoke, is not a member of Moisture.Moisture.'" and the "Me" part of that line is no longer greyed out as it was in the form. it worked before dont know what made the difference.
this is the whole code for that class
Imports System
Imports System.IO.Ports
Imports System.Net.Mime
Public Class Moisture
Dim WithEvents serialPort As New IO.Ports.SerialPort
Public Delegate Sub myDelegate()
Public RawString As New System.Text.StringBuilder
Public value As String
Public Sub StartListening()
If serialPort.IsOpen Then
serialPort.Close()
End If
Try
With serialPort
.PortName = "COM3"
.BaudRate = 9600
.Parity = Parity.None
.StopBits = StopBits.One
.DataBits = 8
.Handshake = Handshake.None
.RtsEnable = True
End With
serialPort.Open()
Catch ex As Exception
End Try
End Sub
Private Sub serialPort_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles SerialPort.DataReceived
Me.Invoke(New myDelegate(AddressOf UPdateVariable), New Object() {})
End Sub
Public Sub UPdateVariable()
With RawString
.Append(serialPort.ReadLine())
End With
If RawString.ToString().Count(Function(x As Char) x = "%"c) = 2 Then
PiTagUpdater(StringParser(RawString.ToString()))
RawString.Clear()
End If
End Sub
Public Function StringParser(RawString As String) As String
Dim Moisture = RawString
Dim value As String
Dim values As String() = Moisture.Split(New Char() {":"c})
value = values(values.Length - 1).Trim({" "c, "%"c})
Return value
End Function
Private Sub PiTagUpdater(Value As Decimal)
Try
Dim piserver As New PCA.Core.PI.PIServer(PCA.Core.Globals.Applications.Application("GENERAL").ConfigValues.ConfigValue("PI_SERVER_NAME").StringValue, PCA.Core.Globals.Applications.Application("GENERAL").ConfigValues.ConfigValue("PI_SERVER_UID").GetDeCryptedStringValue, PCA.Core.Globals.Applications.Application("GENERAL").ConfigValues.ConfigValue("PI_SERVER_PASSWD").GetDeCryptedStringValue, True)
Dim TimeStamp As DateTime = FormatDateTime(Now)
Dim RapidRingCrush = "M1:RapidRingCrush.T"
Try
piserver.WriteValue(RapidRingCrush, Value, TimeStamp)
Catch ex As Exception
MessageBox.Show("Error occured locating Pi Tag", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
Application.Exit()
End Try
Catch ex As Exception
MessageBox.Show("Cannot connect to Pi Server")
End Try
End Sub
End Class

Answer 1

Me refers to the current object, in this case the instance of your class. Your class doesn't have an Invoke() method (like the error says), though anything that derives from System.Windows.Forms.Control does (for instance a Form).
Control.Invoke() is used to move the execution of a method to the same thread that the control was created on. This is used to achieve thread-safety.
Since you switched to a service it is fair to assume that you do not have a user interface, thus there's no need to invoke. Removing the Invoke() call and calling the method manually should be enough:
Private Sub serialPort_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles SerialPort.DataReceived
UPdateVariable()
End Sub
EDIT:
As LarsTech says, you also have to switch the message boxes to some kind of logging methods. A Windows Service usually runs under a different account, which means that it cannot display a user interface to the current user.