Text from a serial port appearing in a rich text box but not being picked up as string?

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C#

serial-port

Hi All,

I am reading a serial port and putting output to a string.
But the string is blank, however if I stick a message box in, it causes enough of a gap to allow the text to appear in the string. I am using a delay based on the length of the expected reply.
The line of code that appears is

reply = rtbIncoming.text

rtbIncoming.Text has a string in it from the device. Is it because of seperate threads the reply in the text box appears on one thread, there is not enough of a delay for it to get from the comms thread to the UI thread? As I have had the following advice

So instead of a line like this:
   rtbIncoming.Text = reply;

I'd try code like this:

this.Invoke(new MethodInvoker(delegate()
{
   rtbIncoming.Text = reply;
}));

This would appear to use a delegate similar to the one I am using the Data Recieved Event.

    private void port_DataReceived_1(object sender,SerialDataReceivedEventArgs e)   
        {
           // MessageBox.Show("Here!!");
           int valueWait = WaitForData(12, 10);
          InputData = myComPort.ReadExisting(); 
          if (InputData != String.Empty)
          {
            this.BeginInvoke(new SetTextCallback(SetText), new object[]
{InputData});
            
          }
            /*
             this.Invoke(new MethodInvoker(delegate()
               {
                ReplyData=  rtbIncoming.Text;
               }));
             */
        }

I think the previous answer I had over looked this as I now have two delegates to the same thread with no success! HELP!!
Glenn