Finite State Machine with Sub-state

using System;
using System.Collections.Generic;
using System.Text;

namespace StateModel
{
    public abstract class StateMgmt
    {
        protected State rootState = null;

        public State GetCurrentState()
        {
            if (this.rootState != null)
            {
                return rootState.GetCurrentState();
            }
            return null;
        }

        public virtual void GoToState(int stateId)
        {
            if (rootState != null)
            {
                rootState.GoToState(stateId);
            }
            else
            {
                throw new Exception("Root state is not initialized");
            }
        }

        public virtual void HandleTrigger(int trigger)
        {
            if (this.rootState != null)
            {
                rootState.HandleTrigger(trigger);
            }
        }
    }
}