Chat Application using Web services in C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Collections;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Diagnostics;
using ChatClient.ChatServices;

namespace ChatClient
{
    public partial class Form1 : Form
    {
        // Creating the object of the web service
        ChatService chat = new ChatService();
        // Arraylist to hold all the currently logged users.
        static public ArrayList arrOUsers = new ArrayList();
        static public string strMe = string.Empty;
        static public string strMess = string.Empty;
        private bool userFlag = true;
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            // Retrieving the Windows UserName.
            lblUserName.Text = System.Windows.Forms.SystemInformation.UserName.ToString();
            strMe = lblUserName.Text;
            // Calling the web service for 'AddUser' for adding himself after logging.
            chat.AddUser(lblUserName.Text);
            timer1.Enabled = true;
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            ShowUsers();
            RecvMessage();
        }

        private void ShowUsers()
        {
            lstUsers.Items.Clear();
            // Calling the web service for 'GetUsers' for retrieving all the currently logged users. 
            string[] strUsers = chat.GetUsers().Split('|');
            for (int i = 0; i < strUsers.Length-1; i++)
            {
                if(strUsers[i].ToUpper() != lblUserName.Text.Trim().ToUpper())
                    lstUsers.Items.Add(strUsers[i], 1);
            }            
        }

        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            e.Cancel = true;
            // On closing hide the form that can be re-opened from the icon in the system tray.
            Hide();
        }

        private void lstUsers_DoubleClick(object sender, EventArgs e)
        {
            userFlag = true;
            // To check whether the chat window for this user is already open.
            for (int i = 0; i < arrOUsers.Count; i++)
            {
                if (lstUsers.FocusedItem.Text.ToString() == arrOUsers[i].ToString())
                    userFlag = false;
            }
            if (userFlag == true)
            {
                arrOUsers.Add(lstUsers.FocusedItem.Text.ToString());
                Form f = new PrivateMessage(lstUsers.FocusedItem.Text.ToString());
                f.Show();
            }
        }

        private void lstUsers_SelectedIndexChanged(object sender, EventArgs e)
        {
            
        }

        private void RecvMessage()
        {
            strMess = chat.ReceiveMessage(lblUserName.Text);
            if (strMess.Trim().Length > 0)
            {
                string[] strUser = strMess.Split(':');
                userFlag = true;
                for (int i = 0; i < arrOUsers.Count; i++)
                {
                    if (strUser[0] == arrOUsers[i].ToString())
                        userFlag = false;
                }
                if (userFlag == true)
                {
                    arrOUsers.Add(strUser[0]);
                    Form f = new PrivateMessage(strUser[0], strMess);
                    f.Show();
                }
            }
        }

        private void toolStripMenuItem2_Click(object sender, EventArgs e)
        {
            chat.RemoveUser(lblUserName.Text);
            notifyIcon1.Visible = false;
            notifyIcon1.Dispose();
            Environment.Exit(0);           
        }

        private void toolStripMenuItem1_Click(object sender, EventArgs e)
        {
            Form f = new About();
            f.Show();
        }

        private void notifyIcon1_MouseClick(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                Show();
            }
        }
    }
}