Hello, Mo!

You have to use Control.Invoke method to access your
UI.

From the docs on DataReceived
"The DataReceived event is raised on a secondary thread when data is
received from the SerialPort object. Because this event is raised on a
secondary thread, and not the main thread, attempting to modify some
elements in the main thread, such as UI elements, could raise a threading
exception. If it is necessary to modify elements in the main Form or
Control, post change requests back using Invoke, which will do the work on
the proper thread.
"

Have a look at ( http://www.codeproject.com/csharp/winformthreading.asp ) to
see how to handle mutlithreading in WinForms

You wrote  on 30 Sep 2006 20:00:57 -0700:

M> Hi,
M> I have an application where I read a serial port data from a barcode
M> and set the labels on a form. I also have a textbox and button where
M> you can enter the data and here is the problem. if I use the textbox
M> and submit using thebutton everything works fine. If I use the
M> SerialDataReceivedEventHandler method  of the serial port, the
M> application crahes. It seens like that when the serial port triggers
M> and I call the same routines it is not aware of the form elements and
M> hence the application hangs up. Any body has ideas on what is the
M> fix?
M> if I debug, I get the following message on when I go over the label
M> in
M> the routine

M> AutoEllipsis = Function evaluation disabled because a previous
M> function
M> evaluation timed out. You must continue execution to reenable
M> function
M> evaluation.

M> Here is the code

M> namespace ShippingLabel
M> {
M>     public partial class xxxx : Form
M>     {
M>         SerialPort sp = new SerialPort();
M>         public NDES2()
M>         {
M>             InitializeComponent();

M> System.Windows.Forms.Control.CheckForIllegalCrossThreadCalls = false;
M>             sp.BaudRate = 9600;
M>             sp.Parity = Parity.None;
M>             sp.DataBits = 8;
M>             sp.StopBits = StopBits.One;
M>             sp.ReadTimeout = 1500;
M>             sp.DataReceived += new
M> SerialDataReceivedEventHandler(sp_DataReceived);
M>             sp.Open();

M>         }
M>         void sp_DataReceived(object sender,
M> SerialDataReceivedEventArgs
M> e)
M>         {
M>             try
M>             {
M>                 string ret = "\r";
M>                 string ID = sp.ReadLine().Replace(ret, "");
M>                 sp.Close();
M>                 TheNumber.Text = ID;
M>                 Generate_Label(ID);
M>                  sp.Open();

M>             }
M>             catch
M>             {
M>                 ErrorLabel.Text += "Scanner Communication Failed";
M>                 sp.Close();
M>             }
M>         }
M>  public void Generate_Label(string theNumber)
M>         {

M> myLabel.text = theNumber;
M> }

With best regards, Vadym Stetsyak.
Blog: http://vadmyst.blogspot.com