Cross-thread operation not valid in vb.net with serial port

Question

I have a form that uses a class to process incoming data in a richtextbox. The data is received via serial port.

When I load the form I initialize the class by doing this:

oDigi = New DigitalProcessing
oDigi.InitHostForm(Me, 1, MyParentNumber)

and that executes this in the class:

Public Sub InitHostForm(ByVal theHostForm As Object, ByVal iInterface As Integer,      Optional ByVal Parent As Integer = 0)
Hostform = theHostForm
ParentNr = Parent
End Sub

In the form I initialize the serialport and everything is good. When text is received from the serial port this routine is called:

Private Sub MSComm1_DataReceived(sender As Object, e As SerialDataReceivedEventArgs) Handles MSComm1.DataReceived
    If Unloaded Then Exit Sub
    oDigi.RxComData(MSComm1.ReadExisting, Val(MyRXid))
End Sub

Thats calls this routine:

Public Sub PrintToRxWindow(ByVal sMsg As String, ByVal Index As Integer)
If Len(Hostform.rtfRX(Index).Text) > lMaxLen Then
LockWindowUpdate(Hostform.rtfRX(Index).Handle)
Hostform.rtfRX(Index).SelectionStart = 0
Hostform.rtfRX(Index).SelectionLength = 500
Hostform.rtfRX(Index).ReadOnly = False
Hostform.rtfRX(Index).SelectedText = ""
Hostform.rtfRX(Index).ReadOnly = True
LockWindowUpdate(0)
End If

In the If line above I get the following error "Cross-thread operation not valid: Control '' accessed from a thread other than the thread it was created on."

This only happens if I use the serial port. If I input text via another method then I do not get an error. Upon doing some searching on Microsoft I found that the Serial port class will run in it's own thread so I understand where the separate threads are coming from. But I do not know how to fix it. I am guessing I need to use .invoke but I can't figure out where it needs to be done.

Answer 1

That is because the DataReceived event is returned from a helper thread. Use a delegate:

Private Sub MSComm1_DataReceived(sender As Object, e As SerialDataReceivedEventArgs) Handles MSComm1.DataReceived
 If Unloaded Then Exit Sub
 'lambda sub acting as delegate
 'all code inside this sub is on UI thread
 Me.Invoke(Sub()
            oDigi.RxComData(MSComm1.ReadExisting, Val(MyRXid))
           End Sub)
End Sub