Finite State Machine in CSharp

State.cs

/*****************************************************************************
 * State.cs
 * 
 * This interface allows an object to be treated as a State by a State
 * Machine.
 ****************************************************************************/

using UnityEngine;
using System.Collections;

namespace FiniteStateMachine
{
    public interface State  
    {
        /// <summary>
        /// Called when the state is made active by the state machine.
        /// </summary>
        void setup();

        /// <summary>
        /// Called each time Update is called by the Unity engine.
        /// </summary>
        void update();

        /// <summary>
        /// Called when the state machine changes state to allow the 
        /// state to clean up.
        /// </summary>
        void teardown();
    }
}

StateMachine.cs

/*****************************************************************************
 * StateMachine.cs
 * 
 * A finite state machine that allows an object to have multiple states
 * and handle updates in a consistent way.
 ****************************************************************************/

using UnityEngine;
using System.Collections;

namespace FiniteStateMachine
{
    public class StateMachine
    {
        /*********************************************************************
         * PRIVATE DATA
         ********************************************************************/

        private State currentState;

        /*********************************************************************
         * CONSTRUCTOR
         ********************************************************************/

        public StateMachine(State initialState)
        {
            this.changeState (initialState);
        }

        /*********************************************************************
         * PUBLIC METHODS
         ********************************************************************/

        /// <summary>
        /// Changes the state.  Calls teardown on current state (if it exists)
        /// and calls setup on the new state.
        /// </summary>
        /// <param name="newState">New state to switch to.</param>
        public void changeState(State newState)
        {
            if(this.currentState != null)
            {
                this.currentState.teardown();
            }

            newState.setup ();

            this.currentState = newState;
        }

        /// <summary>
        /// Update the current state.
        /// 
        /// A null pointer exception will occur if the state is null.
        /// </summary>
        public void update()
        {
            this.currentState.update ();
        }

    }
}