Assistance with SerialPort monitoring (C# Winforms)

Question

I am trying to develop a piece of software which can listen and talk to a serial port(COM3, COM5, etc.). The file 'form1.cs' is copied and pasted below.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO.Ports;

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        string DispString;
        public Form1()
        {
            InitializeComponent();
        }

        private void StartCOM1(object sender, EventArgs e)
        {
            serialPort1.PortName = "COM1";
            StartCOM_General();
        }

        private void StartCOM3(object sender, EventArgs e)
        {
            serialPort1.PortName = "COM3";
            StartCOM_General();
        }

        public void StartCOM_General()
        {
            serialPort1.BaudRate = 115200;
            serialPort1.Parity = Parity.None;
            serialPort1.StopBits = StopBits.One;
            serialPort1.Handshake = Handshake.None;
            try { serialPort1.Open(); } finally{ }
            serialPort1.ReadTimeout = 2000;
            if (serialPort1.IsOpen)
            {
                DispString = "";
            }
        }

        private void ResetClosePort(object sender, EventArgs e)
        {
            DispString = "";
            textBox1.Text = "";
            serialPort1.Close();
        }

        private void UpdateData(object sender, SerialDataReceivedEventArgs e)
        {
            DispString += serialPort1.ReadExisting();
            textBox1.Text = DispString;
        }
    }
}

The issue I have is that my port doesn't display anything. Even though my serialPort object's event for 'DataReceived' is set to call UpdateData, I don't think that UpdateData is being called at all.

This is the image of the form, with the event tab open for serialPort1.

The image adds nothing to the question at all. Also you havent hooked up the event. maybe you should read about events a little — TheGeneral, Oct 05 '19 at 22:09
Please read the section about threading concerns in the [SerialPort.DataReceived documentation](https://learn.microsoft.com/en-us/dotnet/api/system.io.ports.serialport.datareceived?view=netframework-4.8) — Klaus Gütter, Oct 06 '19 at 09:37

score 0 · Answer 1 · answered Oct 05 '19 at 22:14

You could check with

MessageBox.Show("Data recieved!");

in UpdateData(..) to see if UpdateData is getting called.
If it is maybe try replacing

DispString += serialPort1.ReadExisting();

with

SerialPort sp = (SerialPort)sender;
DispString += sp.ReadExisting();

score 0 · Accepted Answer · answered Oct 06 '19 at 09:46

As stated in the SerialPort.DataReceived documentation, the event is signaled on a secondary thread. Therefore, you have to properly marshal back to the UI thread using Control.Invoke, e.g.:

    private void UpdateData(object sender, SerialDataReceivedEventArgs e)
    {
        DispString += serialPort1.ReadExisting();
        textBox1.Invoke((MethodInvoker)(() => textBox1.Text = DispString));
    }

Assistance with SerialPort monitoring (C# Winforms)

2 Answers2