C# 3.0下有限状态机的一种优雅的实现
C# 3.0下有限状态机的一种优雅的实现
实现状态机有多种模式，其中最灵活而强大的方式是通过迁移表来实现，该方式的缺点之一是需要编写大量小块代码去支持迁移表。而在C#3.0中，可以以一种非常优雅的方式实现。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace StateMachine
{
class Program
{
static void Main(string[] args)
{
var door = new Door(State.Open);
while (true)
{
string s = Console.ReadLine();
Operation op = string.IsNullOrEmpty(s) ? Operation.Push : Operation.Pull;
door.Process(op);
}
}
}
enum Operation
{
Push, Pull
}
enum State
{
Open, Closed
}
class Door
{
public State State { get; set; }
Dictionary<State, Dictionary<Operation, Action>> rule;
public Door(State state)
{
this.State = state;
rule = new Dictionary<State, Dictionary<Operation, Action>>();
foreach (var e in Enum.GetValues(typeof(State)))
{
rule[(State)e] = new Dictionary<Operation, Action>();
}
InitOperationRule();
}
void InitOperationRule()
{
//正常操作
rule[State.Closed][Operation.Push] = () => { Console.WriteLine("门被推开了"); State = State.Open; };
rule[State.Open][Operation.Pull] = () => { Console.WriteLine("门被拉上了"); State = State.Closed; };
////加入几种特殊情况的处理
//rule[State.Closed][Operation.Pull] = () => Console.WriteLine("门是关上的，拉了也白拉");
//rule[State.Open][Operation.Push] = () => Console.WriteLine("门是开的，不用推了，直接进去吧");
}
public void Process(Operation op)
{
try
{
rule[State][op]();
}
catch (KeyNotFoundException)
{
Console.WriteLine(string.Format("门在{0}状态下不允许{1}操作", State, op));
}
}
}
}
从代码中可以看到，通过lambda表达式，可以简化迁移表的构造，并且更加直观。
通过迁移表构造状态机的一种不足在于查询速度，在本例中每个操作都要进行两次查询才能进行状态转换操作。如果状态较多则非常费时，这里我把它改进了一下，使得每次操作只需要查询一次即可。
class DoorPlus
{
State state;
public State State
{
get { return state; }
set
{
if (state != value)
currentOpRule = rule[value];
state = value;
}
}
Dictionary<Operation, Action> currentOpRule;
Dictionary<State, Dictionary<Operation, Action>> rule;
public DoorPlus(State state)
{
this.State = state;
rule = new Dictionary<State, Dictionary<Operation, Action>>();
foreach (var e in Enum.GetValues(typeof(State)))
{
rule[(State)e] = new Dictionary<Operation, Action>();
}
currentOpRule = rule[State];
InitOperationRule();
}
void InitOperationRule()
{
//正常操作
rule[State.Closed][Operation.Push] = () => { Console.WriteLine("门被推开了"); State = State.Open; };
rule[State.Open][Operation.Pull] = () => { Console.WriteLine("门被拉上了"); State = State.Closed; };
////加入几种特殊情况的处理
//rule[State.Closed][Operation.Pull] = () => Console.WriteLine("门是关上的，拉了也白拉");
//rule[State.Open][Operation.Push] = () => Console.WriteLine("门是开的，不用推了，直接进去吧");
}
public void Process(Operation op)
{
try
{
currentOpRule[op]();
}
catch (KeyNotFoundException)
{
Console.WriteLine(string.Format("门在{0}状态下不允许{1}操作", State, op));
}
}
}
