ServerMainForm.cs

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.Net.Sockets;
using System.Net;

namespace Server
{
    public partial class ServerMainForm : Form
    {
        TcpListener Listener;
        List<Client> ClientList = new List<Client>();

        public ServerMainForm()
        {
            InitializeComponent();
            StartStropListening();
        }

        private void StartStropListening()
        {
            try
            {
                if (button1.Text == "Start")
                {
                    Listener = new TcpListener(IPAddress.Any, Convert.ToInt32(textBox1.Text));
                    Listener.Start();
                    Listener.BeginAcceptTcpClient(new AsyncCallback(AcceptClient), Listener);
                    button1.Text = "Stop";

                }
                else
                {
                    Listener.Stop();
                    button1.Text = "Start";

                }


            }
            catch (Exception)
            {

                throw;
            }
        }

        private void AcceptClient(IAsyncResult ar)
        {
            try
            {
                Client client = new Client(Listener.EndAcceptTcpClient(ar));

                client.DataRecievedEvent += DataRecieved;

                client.ClientExitedEvent += ClientExited;

                ClientList.Add(client);

                SetText("Clients connected: " + ClientList.Count);
                // ClientsConnectedLabel.Text = "Clients connected: " + ClientList.Count;

                //call this to accept next client...
                Listener.BeginAcceptTcpClient(new AsyncCallback(AcceptClient), Listener);


            }
            catch (Exception)
            {

                throw;
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            StartStropListening();
        }

        private void DataRecieved(Byte[] data)
        {
            //just to let the server know that globally there is data recieved...

        }

        private void ClientExited(Client client)
        {
            // the client exited event was raised thus we need to remove them fromt he list...
            ClientList.Remove(client);
            SetText("Clients connected: " + ClientList.Count);

        }

        delegate void SetTextCallback(string text);
        private void SetText(string text)
        {
            // InvokeRequired required compares the thread ID of the
            // calling thread to the thread ID of the creating thread.
            // If these threads are different, it returns true.
            if (ClientsConnectedLabel.InvokeRequired)
            {
                SetTextCallback d = new SetTextCallback(SetText);
                this.Invoke(d, new object[] { text });
            }
            else
            {
                this.ClientsConnectedLabel.Text = text;
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            ClientList[0].SendMessage("hello world! :P ");
        }
    }
}