Continuous chat

The following implements bidirectional chat functionality using multithreading to prevent UI freezes.

The WinForm implementation uses BackgroundWorker for loop‑based receiving on a separate thread, while message sending is triggered from the UI thread. This bypasses the limitation and enables unrestricted two‑way chat.

Server‑side code first

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Windows.Forms;

namespace Service
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            Control.CheckForIllegalCrossThreadCalls = false;
        }

        IPAddress ip;
        TcpListener listener;
        TcpClient tcpClient;

        private void buttonStart_Click(object sender, EventArgs e)
        {
            this.backgroundWorker1.RunWorkerAsync();
        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            ip = IPAddress.Parse(this.textBoxIP.Text);
            listener = new TcpListener(ip, Convert.ToInt32(this.textBoxPort.Text));
            listener.Start();
            this.textBoxInfo.Text = "Server started - " + DateTime.Now.ToShortTimeString() + "\r\n" + this.textBoxInfo.Text;
            tcpClient = listener.AcceptTcpClient();
            this.textBoxInfo.Text = "Connection established - " + DateTime.Now.ToShortTimeString() + "\r\n" + this.textBoxInfo.Text;

            NetworkStream stream = tcpClient.GetStream();
            byte[] byteArray = new byte[1024];
            while (true)
            {
                int length = stream.Read(byteArray, 0, 1024);
                string receiveMessage = Encoding.Unicode.GetString(byteArray, 0, length);
                this.textBoxInfo.Text = "Received: " + receiveMessage + " - " + DateTime.Now.ToShortTimeString() + "\r\n" + this.textBoxInfo.Text;
            }
        }

        private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {

        }

        private void buttonSend_Click(object sender, EventArgs e)
        {
            string message = this.textBoxInput.Text;
            this.textBoxInfo.Text = "Sent \"" + message + "\" - " + DateTime.Now.ToShortTimeString() + "\r\n" + this.textBoxInfo.Text;
            NetworkStream stream = tcpClient.GetStream();
            byte[] byteArray = Encoding.Unicode.GetBytes(message);
            stream.Write(byteArray, 0, byteArray.Length);
        }
    }
}
Code language: C# (cs)

Client‑side implementation

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Net.Sockets;
using System.Text;
using System.Windows.Forms;

namespace Client
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            Control.CheckForIllegalCrossThreadCalls = false;
        }
        TcpClient tcpClient;
        private void buttonStart_Click(object sender, EventArgs e)
        {
            tcpClient = new TcpClient();
            try
            {
                tcpClient.Connect(this.textBoxIP.Text, Convert.ToInt32(this.textBoxPort.Text));
                this.textBoxInfo.Text = "Connection established - " + DateTime.Now.ToShortTimeString() + "\r\n" + this.textBoxInfo.Text;
                this.backgroundWorker1.RunWorkerAsync();
            }
            catch (Exception ex)
            {
                MessageBox.Show("Connection failed - "+ex.Message);
            }
        }

        private void buttonSend_Click(object sender, EventArgs e)
        {
            string message = this.textBoxInput.Text;
            this.textBoxInfo.Text = "Sent \""+message+"\" - " + DateTime.Now.ToShortTimeString() + "\r\n" + this.textBoxInfo.Text;
            NetworkStream stream = tcpClient.GetStream();
            byte[] byteArray = Encoding.Unicode.GetBytes(message);
            stream.Write(byteArray, 0, byteArray.Length);
        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            NetworkStream stream = tcpClient.GetStream();
            byte[] byteArray = new byte[1024];
            while (true)
            {
                int length = stream.Read(byteArray, 0, 1024);
                string receiveMessage = Encoding.Unicode.GetString(byteArray, 0, length);
                this.textBoxInfo.Text = "Received: " + receiveMessage + " - " + DateTime.Now.ToShortTimeString() + "\r\n" + this.textBoxInfo.Text;
            }
        }
    }
}
Code language: C# (cs)

Continuous chat