Another Generic State Machine

Introduction

I was looking for a generic implementation of the State Machine pattern. Of course, there are many out there. But what I found was either too specific or part of some monster framework. So I wrote my own.

Background

The State Machine pattern is discussed here.

Using the Code

To use the StateMachine, simply derive from the class and setup your states and transition events:

public class MyStateMachine : StateMachine<StateData, int, string>
{
   public MyStateMachine ()
   {
       AddState(new State { data = new StateData { Identity = 0, Name = "Solid" }, 
                            IdSelector = x=> x.Identity });
       AddState(new State { data = new StateData { Identity = 1, Name = "Liquid" }, 
                            IdSelector = x => x.Identity });
       AddState(new State { data = new StateData { Identity = 2, Name = "Gas" }, 
                            IdSelector = x => x.Identity });
       AddEvent(new StateMachine<StateData, int, string>.Event { ID = "Cool", 
                   Transitions = new Dictionary<int, int> { { 0, 0 }, { 1, 0 }, { 2, 1 } } });
       AddEvent(new StateMachine<StateData, int, string>.Event { ID = "Heat", 
                   Transitions = new Dictionary<int, int> { { 0, 1 }, { 1, 2 }, { 2, 2 } } });
   } 
   public void Heat()
   {
       var ev = GetEventByKey("Heat");
       FireEvent(ev);
   }
   public void Cool()
   {
      var ev = GetEventByKey("Cool");
      FireEvent(ev);
   }

} 

An event in this StateMachine is the action that happens in the world, this then triggers transitions in the state machine from one state to another. You can setup public methods to match the actions set on your StateMachine.

In this simplified example, the state machine matches the state of matter depending on its heat property. Cooling a gas will result in a liquid. Heating a solid will result in a liquid.

Using the state machine is easy:

var target = new MyStateMachine();
target.LeaveState += LeaveHandler; 
target.SetState(1); 
target.SetState(1); 

Points of Interest

I ran into interesting questions while writing unit tests for this class. See tip on "Mocking Event Handlers".