How can I Set Simple Timer in Service class

hi
i use of below code
` public override StartCommandResult OnStartCommand(Intent intent, [GeneratedEnum] StartCommandFlags flags, int startId)
{

        Toast.MakeText(this, "Start", ToastLength.Short).Show();
        System.Timers.Timer timer = new System.Timers.Timer();
        timer.Interval = 5000;
        timer.Elapsed += Timer_Elapsed;
        timer.Start();
        return base.OnStartCommand(intent, flags, startId);
    }`

but timer not running
why?
and what must i do?