public void Pretplati(int id)
        {
            IMeasureServiceCallback callbackChannel = OperationContext.Current.GetCallbackChannel <IMeasureServiceCallback>();

            if (!observers.ContainsKey(id))
            {
                observers[id] = new List <IMeasureServiceCallback>();
                Console.WriteLine("Ne postoji id.");
            }
            else
            {
                observers[id].Add(callbackChannel);
            }
        }
        public void Odjavi(int id)
        {
            IMeasureServiceCallback callbackChannel = OperationContext.Current.GetCallbackChannel <IMeasureServiceCallback>();

            observers[id].Remove(callbackChannel);
        }