Chat Application using Web services in C#

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

namespace ChatClient
{
    public partial class PrivateMessage : Form
    {
        [DllImport("user32.dll")]
        static extern Int32 FlashWindowEx(ref FLASHWINFO pwfi);

        [StructLayout(LayoutKind.Sequential)]
        public struct FLASHWINFO
        {
            public UInt32 cbSize;
            public IntPtr hwnd;
            public UInt32 dwFlags;
            public UInt32 uCount;
            public UInt32 dwTimeout;
        }

        //Stop flashing. The system restores the window to its original state. 
        public const UInt32 FLASHW_STOP = 0;
        //Flash the window caption. 
        public const UInt32 FLASHW_CAPTION = 1;
        //Flash the taskbar button. 
        public const UInt32 FLASHW_TRAY = 2;
        //Flash both the window caption and taskbar button.
        //This is equivalent to setting the FLASHW_CAPTION | FLASHW_TRAY flags. 
        public const UInt32 FLASHW_ALL = 3;
        //Flash continuously, until the FLASHW_STOP flag is set. 
        public const UInt32 FLASHW_TIMER = 4;
        //Flash continuously until the window comes to the foreground. 
        public const UInt32 FLASHW_TIMERNOFG = 12; 

        ChatService chat = new ChatService();
        private string strUser;
        private Font font;
        public PrivateMessage(string strUserName)
        {
            InitializeComponent();
            strUser = strUserName;
        }

        public PrivateMessage(string strUserName, string strMg)
        {
            InitializeComponent();
            strUser = strUserName;
            string[] strU = Form1.strMess.Split(':');
            string strM = string.Empty;
            
            for (int i = 1; i < strU.Length; i++)
            {
                strM = strM + strU[i];
            }
            rtbMessage.SelectedText = strU[0] + ": ";
            rtbMessage.SelectedRtf = strM;
            Form1.strMess = "";
        }

        private void btnSend_Click(object sender, EventArgs e)
        {
            if (rtbWriteMsg.Text.Trim().Length > 0)
            {
                chat.SendMessage(Form1.strMe, strUser, rtbWriteMsg.Rtf);
                rtbMessage.SelectedText = Form1.strMe + ": ";
                rtbMessage.SelectedRtf = rtbWriteMsg.Rtf;
                rtbMessage.ScrollToCaret();
                rtbWriteMsg.Clear();
                rtbWriteMsg.Focus();
            }
        }

        private void PrivateMessage_Load(object sender, EventArgs e)
        {            
            timer1.Enabled = true;
            Text = strUser;
        }

        private void PrivateMessage_FormClosing(object sender, FormClosingEventArgs e)
        {
            Form1.arrOUsers.Remove(strUser);
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            if (Form1.strMess.Trim().Length > 0)
            {
                string[] strU = Form1.strMess.Split(':');
                string strM = string.Empty;
                if (strU[0] == strUser)
                {
                    for (int i = 1; i < strU.Length; i++)
                    {
                        strM = strM + strU[i];
                    }
                    rtbMessage.SelectedText = strU[0] + ": ";
                    rtbMessage.SelectedRtf = strM;
                    Form1.strMess = "";                    
                    rtbMessage.ScrollToCaret();
                    FlashWindowEx(this);
                }
            }
        }    

        public static bool FlashWindowEx(Form frm)
        {
            IntPtr hWnd = frm.Handle;
            FLASHWINFO fInfo = new FLASHWINFO();

            fInfo.cbSize = Convert.ToUInt32(Marshal.SizeOf(fInfo));
            fInfo.hwnd = hWnd;
            fInfo.dwFlags = FLASHW_ALL | FLASHW_TIMERNOFG;
            fInfo.uCount = UInt32.MaxValue;
            fInfo.dwTimeout = 0;

            return (FlashWindowEx(ref fInfo) == 0);
        }

        private void rtbWriteMsg_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar == '\r')
            {
                if (rtbWriteMsg.Text.Trim().Length > 0)
                {
                    chat.SendMessage(Form1.strMe, strUser, rtbWriteMsg.Rtf);
                    rtbMessage.SelectedText = Form1.strMe + ": ";
                    rtbMessage.SelectedRtf = rtbWriteMsg.Rtf;
                    rtbMessage.ScrollToCaret();
                    rtbWriteMsg.Clear();
                    rtbWriteMsg.Focus();
                }
            }
        }

        private void btnFont_Click(object sender, EventArgs e)
        {
            fontDialog1.ShowDialog();
            font = new Font(fontDialog1.Font.Name, fontDialog1.Font.Size, fontDialog1.Font.Style);
            rtbWriteMsg.Font = font;
            rtbWriteMsg.Focus();
            font.Dispose();
        }

        private void btnColor_Click(object sender, EventArgs e)
        {
            colorDialog1.ShowDialog();
            rtbWriteMsg.ForeColor = colorDialog1.Color;
            rtbWriteMsg.Focus();
        }       
    }
}