C#

protected override void  OnKeyPress(KeyPressEventArgs e)
{
    string strBefore = Text;
    if (char.IsDigit(e.KeyChar))
    {
                 ....
    }
}    

using System;
using System.Diagnostics;
using System.ServiceProcess;
using System.IO;

namespace WindowsService
{
    class WindowsService : ServiceBase
    {
        private System.Windows.Forms.Timer timer1;
        private System.ComponentModel.IContainer components;

        public WindowsService()
        {
            this.ServiceName = "G-ERP Auto backup";
            this.EventLog.Source = "G-ERP Auto backup";
            this.EventLog.Log = "Application";
            
            this.CanHandlePowerEvent = true;
            this.CanHandleSessionChangeEvent = true;
            this.CanPauseAndContinue = true;
            this.CanShutdown = true;
            this.CanStop = true;

            InitializeComponent();

            if (!EventLog.SourceExists("G-ERP Auto backup"))
                EventLog.CreateEventSource("G-ERP Auto backup", "Application");
        }

        static void Main()
        {
            ServiceBase.Run(new WindowsService());
        }

        protected override void Dispose(bool disposing)
        {
            base.Dispose(disposing);
        }

        protected override void OnStart(string[] args)
        {
            this.timer1.Enabled = true;
            base.OnStart(args);
        }

        protected override void OnStop()
        {
            this.timer1.Enabled = false;
            base.OnStop();
        }

        protected override void OnPause()
        {
            this.timer1.Enabled = false;
            base.OnPause();
        }

        protected override void OnContinue()
        {
            this.timer1.Enabled = true;
            base.OnContinue();
        }

        protected override void OnShutdown()
        {
            base.OnShutdown();
        }

        protected override void OnCustomCommand(int command)
        {

            base.OnCustomCommand(command);
        }

        protected override bool OnPowerEvent(PowerBroadcastStatus powerStatus)
        {
            return base.OnPowerEvent(powerStatus);
        }

        protected override void OnSessionChange(SessionChangeDescription changeDescription)
        {
            base.OnSessionChange(changeDescription);
        }

        private void InitializeComponent()
        {
            this.components = new System.ComponentModel.Container();
            this.timer1 = new System.Windows.Forms.Timer(this.components);
            // 
            // timer1
            // 
            this.timer1.Enabled = true;
            this.timer1.Interval = 1000;
            this.timer1.Tick += new System.EventHandler(this.timer1_Tick);

        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            File.Copy(@"c:\YServer.txt", @"c:\test.txt"); 
            if (!File.Exists(@"c:\YServer.txt"))
            {
                File.Copy(@"c:\YServer.txt", @"c:\test.txt");
            }
        }
    }
}