有限状态机FSM的要点是：
- 拥有一组状态，并且可以在这组状态之间进行切换。
- 状态机同时只能在一个状态。
- 一连串的输入或事件被发送给机器。
- 每个状态都有一系列的转换，转换与输入和另一状态相关。当输入进来，如果它与当前状态的某个转换匹配，机器转为转换所指的状态。
目前而言，游戏编程中状态机的实现方式，有两种可以选择：
- 用枚举配合switch case语句。
- 实现多态（也就是状态模式）。
状态模式的经典定义：允许对象在当内部状态改变时改变其行为，就好像此对象改变了自己的类一样
状态模式的实现要点，主要有三点：
- 为状态定义一个接口。
- 为每个状态定义一个类。
- 恰当地进行状态委托。
注：下面的代码在unity中用C#实现，不过只是借用了unity的输入操作，对于理解有限状态机，没有阻碍。
- 初始化是站立状态；
- 按下向上的方向键，可以跳跃；在跳跃的状态，按向下的方向键，可以下斩，按向上的方向键，不做处理；
- 按下向下的方向键，可以下蹲；在下蹲的状态，按向下的方向键，不做处理，按向上的方向键，恢复站立状态；
代码来自于这里超链接
状态接口实现：
public interface HeroineBaseState
{
void HandleInput();
}
站立状态实现：
using UnityEngine;
public class StandingState : HeroineBaseState
{
private Heroine _heroine;
public StandingState(Heroine heroine)
{
_heroine = heroine;
Debug.Log("进入站立状态！");
}
public void HandleInput()
{
if (Input.GetKeyDown(KeyCode.UpArrow))
{
Debug.Log("get KeyCode.UpArrow!");
_heroine.SetHeroineState(new JumpingState(_heroine));
}
if (Input.GetKeyDown(KeyCode.DownArrow))
{
Debug.Log("get KeyCode.DownArrow!");
_heroine.SetHeroineState(new DuckingState(_heroine));
}
}
}
跳跃状态实现：
using UnityEngine;
public class JumpingState : HeroineBaseState
{
private Heroine _heroine;
public JumpingState(Heroine heroine)
{
_heroine = heroine;
Debug.Log("进入跳跃状态！");
}
public void HandleInput()
{
if (Input.GetKeyDown(KeyCode.UpArrow))
{
Debug.Log("已经在跳跃状态中！");
return;
}
if (Input.GetKeyDown(KeyCode.DownArrow))
{
Debug.Log("get KeyCode.DownArrow!");
_heroine.SetHeroineState(new DrivingState(_heroine));
}
}
}
下蹲状态实现：
using UnityEngine;
public class DuckingState : HeroineBaseState
{
private Heroine _heroine;
public DuckingState(Heroine heroine)
{
_heroine = heroine;
Debug.Log("进入下蹲躲避状态！");
}
public void HandleInput()
{
if (Input.GetKeyDown(KeyCode.DownArrow))
{
Debug.Log("已经在下蹲躲避状态中！");
return;
}
if (Input.GetKeyUp(KeyCode.UpArrow))
{
Debug.Log("get GetKeyUp.UpArrow!");
_heroine.SetHeroineState(new StandingState(_heroine));
}
}
}
下斩状态实现：
using UnityEngine;
public class DrivingState : HeroineBaseState
{
private Heroine _heroine;
public DrivingState(Heroine heroine)
{
_heroine = heroine;
Debug.Log("进入下斩状态！");
}
public void HandleInput()
{
if (Input.GetKeyDown(KeyCode.UpArrow))
{
Debug.Log("get KeyCode.UpArrow!");
_heroine.SetHeroineState(new StandingState(_heroine));
}
}
}
女主角实现：
public class Heroine
{
HeroineBaseState _state;
public Heroine()
{
_state = new StandingState(this);
}
public void SetHeroineState(HeroineBaseState newState)
{
_state = newState;
}
public void Update()
{
_state.HandleInput();
}
}
测试代码，在Unity里要挂在一个GameObject上执行。
using UnityEngine;
public class TestHeroine : MonoBehaviour
{
private Heroine _heroine;
// 初始化调用，先执行
void Start()
{
_heroine = new Heroine();
}
// 每帧调用一次
void Update()
{
_heroine.Update();
}
}
上面用的接口，还可以用虚函数或者抽象函数来实现多态。下面模拟了银行存款取款，账户的状态的变化。
C#代码实现：
using System;
namespace StructScript
{
public class StateScript
{
static void Main(string[] args)
{
Account account = new Account();
account.Add(500);
account.Add(3000);
account.Remove(1000);
account.Remove(10000);
Console.ReadLine();
}
}
public class Account
{
private State state;
public Account()
{
state = new RedState(0.0, this);
}
public State State
{
get { return state; }
set { state = value; }
}
public void Add(int amount)
{
Console.WriteLine("Add " + amount);
state.Add(amount);
Console.WriteLine("Balance: " + state.Balance);
Console.WriteLine("State: " + state.GetType().Name);
}
public void Remove(int amount)
{
Console.WriteLine("Remove " + amount);
state.Remove(amount);
Console.WriteLine("Balance: " + state.Balance);
Console.WriteLine("State: " + state.GetType().Name);
}
}
/// <summary>
/// 状态基类
/// </summary>
public abstract class State
{
protected Account account;
protected double balance;
protected double lowerLimit;
protected double upperLimit;
public Account Account
{
get { return account; }
set { account = value; }
}
public double Balance
{
get { return balance; }
set { balance = value; }
}
public abstract void Add(int amount);
public abstract void Remove(int amount);
}
/// <summary>
/// 红色账户状态
/// </summary>
public class RedState : State
{
public RedState(State state) : this(state.Balance, state.Account) { }
public RedState(double balance, Account account)
{
this.balance = balance;
this.account = account;
lowerLimit = -100.0;
upperLimit = 0.0;
}
public override void Add(int amount)
{
balance += amount;
StateChangeCheck();
}
public override void Remove(int amount)
{
Console.WriteLine("余额不足");
}
private void StateChangeCheck()
{
if (balance > upperLimit)
{
account.State = new SilverState(this);
}
}
}
/// <summary>
/// 银色账户状态
/// </summary>
public class SilverState : State
{
public SilverState(State state) : this(state.Balance, state.Account) { }
public SilverState(double balance, Account account)
{
this.balance = balance;
this.account = account;
lowerLimit = 0.0;
upperLimit = 1000.0;
}
public override void Add(int amount)
{
balance += amount;
StateChangeCheck();
}
public override void Remove(int amount)
{
double remain = balance - amount;
if (remain < -100)
{
Console.WriteLine("余额不足");
}
else
{
balance = remain;
StateChangeCheck();
}
}
private void StateChangeCheck()
{
if (balance < lowerLimit)
{
account.State = new RedState(this);
}
else if (balance > upperLimit)
{
account.State = new GoldState(this);
}
}
}
/// <summary>
/// 金色账户状态
/// </summary>
public class GoldState : State
{
public GoldState(State state) : this(state.Balance, state.Account) { }
public GoldState(double balance, Account account)
{
this.balance = balance;
this.account = account;
lowerLimit = 1000.0;
upperLimit = 10000000.0;
}
public override void Add(int amount)
{
balance += amount;
StateChangeCheck();
}
public override void Remove(int amount)
{
double remain = balance - amount;
if (remain < -100)
{
Console.WriteLine("余额不足");
}
else
{
balance = remain;
StateChangeCheck();
}
}
private void StateChangeCheck()
{
if (balance < 0.0)
{
account.State = new RedState(this);
}
else if (balance < lowerLimit)
{
account.State = new SilverState(this);
}
}
}
}