[RESOLVED] VB.net 2005 BackGroundWorker help

[MoLaw]

I am trying to write a program to read and write to a radio scanner I have via the serial port. I have the writing down (It was easy enough) and I can read the data from the scanner using the datarecieved event. I can display the read data in a messagebox with no problem but when I try to write it to a TextBox I run into a cross Threading issue. I have been reading up on the BackGroundWorker but I am having trouble wraping my head around it. A couple of questions I have is

What should I do in the DoWork event?
Run the Datarevieved event
or
the actual write to textbox event

Also some of the syntax is confusing to me

Here is the code, any help is appreciated (This project is just for personal learning so any coments about the code is appreciated)

Imports System.Text
Imports System.IO.Ports
Imports System.Threading
Imports System.ComponentModel
 
 
Public Class Main
 
    Dim WithEvents WorkingPort As New SerialPort("com1", 19200)
 
 
    Private Function EnterCommand(ByVal Input As String) As String
        'Add vbcr to the ebd of all commands because the scanner protocall requires it
        Dim addVbcr As String = Input & vbCr
        Return addVbcr
    End Function
 
    Private Sub RecieveScannerData(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles WorkingPort.DataReceived
        'Gets data sent by the scanner and displays it in a msgbox
        ' Also calls the WriteScannerData Sub which does not work and is comented out
        Dim ScannerInput As String
        ScannerInput = WorkingPort.ReadExisting
        MsgBox("data received: " & ScannerInput)
        'WriteScannerData(ScannerInput)
    End Sub
 
    Private Sub WriteScannerData(ByVal MyDebStr As String)
        'Writes scanner data to the txtFeedback TextBox
        MsgBox(" passed Value : " & MyDebStr)
        txtFeedback.AppendText(MyDebStr)
    End Sub
 
    Private Sub btnOpenPort_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOpenPort.Click
        'Opens serialport
        If WorkingPort.IsOpen = False Then
            WorkingPort.Open()
            btnOpenPort.Enabled = False
            btnClosePort.Enabled = True
            btnEnterCommand.Enabled = True
        Else
            MessageBox.Show("Port is all ready open")
        End If
        lblPortStatus.Text = WorkingPort.IsOpen
    End Sub
 
    Private Sub Main_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
 
        lblPortStatus.Text = WorkingPort.IsOpen
        If WorkingPort.IsOpen = False Then
            btnOpenPort.Enabled = True
            btnClosePort.Enabled = False
            btnEnterCommand.Enabled = False
        Else
            btnOpenPort.Enabled = False
            btnClosePort.Enabled = True
        End If
    End Sub
 
    Private Sub btnClosePort_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClosePort.Click
        'Closes serialport
        If WorkingPort.IsOpen = True Then
            WorkingPort.Close()
            btnClosePort.Enabled = False
            btnOpenPort.Enabled = True
            btnEnterCommand.Enabled = False
        Else
            MessageBox.Show("Port is all ready closed")
        End If
        lblPortStatus.Text = WorkingPort.IsOpen
    End Sub
 
    Private Sub btnEnterCommand_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEnterCommand.Click
        'Sends the command chosen from the combobox "cboCommand" the the scanner via the EnterCommand function 
        Dim CommandText As String = cboCommand.Text
        If WorkingPort.IsOpen = False Then
            MessageBox.Show("You need to open the port first")
            Exit Sub
        ElseIf CommandText.Length = 0 Then
            MessageBox.Show("Please Choose a command to send first")
        Else
            WorkingPort.Write(EnterCommand(CommandText))
 
        End If
    End Sub
End Class

[jmcilhinney]

You cannot access controls from threads other than the main thread, except for the Invoke, BeginInvoke, EndInvoke and CreateGraphics methods. You need to use a delegate to marshall the method call to the main thread. Here is an example of using a delegate to set the Text of a TextBox from a BackgroundWorker.

'This delegate matches the signature of the SetTextBoxText method so can be used to Invoke it.
    Private Delegate Sub SetTextBoxTextDelegate(ByVal text As String)
 
    'This method starts the background thread.
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Me.BackgroundWorker1.RunWorkerAsync()
    End Sub
 
    'This method sets the TextBox.Text property.
    Private Sub SetTextBoxText(ByVal text As String)
        Me.TextBox1.Text = text
    End Sub
 
    'This method does the work of the background thread.
    Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
        Me.Invoke(New SetTextBoxTextDelegate(AddressOf SetTextBoxText), "Greetings from the BackgroundWorker.")
    End Sub

Note that I have defined a method specifically to set the Text property of the TextBox and a matching delegate. The DoWork event handler is executed in the background thread, so it is necessary to Invoke the desired method via an instance of the delegate. Basically it is the delegate that carries the method call across the thread boundary, thus allowing it to be executed on the main thread.

[MoLaw]

Works like a charm here is what I ended up with, Thanx again for you time and expertise

Imports System.Text
Imports System.IO.Ports
Imports System.Threading
Imports System.ComponentModel
 
 
Public Class Main
 
    Dim WithEvents WorkingPort As New SerialPort("com1", 19200)
    Dim ScannerInput As String
 
    Private Function EnterCommand(ByVal Input As String) As String
        'Add vbcr to the ebd of all commands because the scanner protocall requires it
        Dim addVbcr As String = Input & vbCr
        Return addVbcr
    End Function
 
    Private Sub RecieveScannerData(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles WorkingPort.DataReceived
        'Gets data sent by the scanner and displays it in a msgbox
        ' Also calls the WriteScannerData Sub which does not work and is comented out
        ScannerInput = WorkingPort.ReadExisting
        MsgBox("data received: " & ScannerInput)
        backgroundWorker1.RunWorkerAsync()
        'WriteScannerData(ScannerInput)
    End Sub
 
    Private Sub WriteScannerData(ByVal MyDebStr As String)
        'Writes scanner data to the txtFeedback TextBox
        'MsgBox(" passed Value : " & MyDebStr)
        txtFeedback.AppendText(MyDebStr)
    End Sub
 
    Private Sub btnOpenPort_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOpenPort.Click
        'Opens serialport
        If WorkingPort.IsOpen = False Then
            WorkingPort.Open()
            btnOpenPort.Enabled = False
            btnClosePort.Enabled = True
            btnEnterCommand.Enabled = True
        Else
            MessageBox.Show("Port is all ready open")
        End If
        lblPortStatus.Text = WorkingPort.IsOpen
    End Sub
 
    Private Sub Main_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        lblPortStatus.Text = WorkingPort.IsOpen
        If WorkingPort.IsOpen = False Then
            btnOpenPort.Enabled = True
            btnClosePort.Enabled = False
            btnEnterCommand.Enabled = False
        Else
            btnOpenPort.Enabled = False
            btnClosePort.Enabled = True
        End If
 
    End Sub
 
    Private Sub btnClosePort_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClosePort.Click
        'Closes serialport
        If WorkingPort.IsOpen = True Then
            WorkingPort.Close()
            btnClosePort.Enabled = False
            btnOpenPort.Enabled = True
            btnEnterCommand.Enabled = False
        Else
            MessageBox.Show("Port is all ready closed")
        End If
        lblPortStatus.Text = WorkingPort.IsOpen
    End Sub
 
    Private Sub btnEnterCommand_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEnterCommand.Click
        'Sends the command chosen from the combobox "cboCommand" the the scanner via the EnterCommand function 
        Dim CommandText As String = cboCommand.Text
        If WorkingPort.IsOpen = False Then
            MessageBox.Show("You need to open the port first")
            Exit Sub
        ElseIf CommandText.Length = 0 Then
            MessageBox.Show("Please Choose a command to send first")
        Else
            WorkingPort.Write(EnterCommand(CommandText))
        End If
    End Sub
 
    Private Delegate Sub SetTextBoxTextDelegate(ByVal text As String)
 
    Private Sub backgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles backgroundWorker1.DoWork
        Me.Invoke(New SetTextBoxTextDelegate(AddressOf WriteScannerData), ScannerInput)
    End Sub
End Class

[jmcilhinney]

I would just recommend that you rename "SetTextBoxTextDelegate" to "WriteScannerDataDelegate", just so that the intended link between the two is obvious. You might not use such similar names if you wanted to use the same delegate to invoke several methods, but if there is a 1:1 correspondence then it is appropriate. Note also that if you ever need to do invoke a method that takes no arguments you don't have to declare your own delegate. You can simply use an instance of the MethodInvoker delegate.