Unity 下简易状态机的实现

国庆到处都是人，我的建议是要么出国旅游，要么就宅在家把时间留给自己或家人。朋友约我去星巴克坐着重构代码，想想也是程序猿之间才有的默契。

关于状态机，我想都知道它很常用，就像单例一样，缺了它们，我们在游戏编程世界里呼吸都不畅快。网上也有很多大神写的状态机，比如PlayMaker这样重量级的插件，功能很强大，依赖也不少。程序猿的胃口有时候就是很挑剔，吃惯了大鱼大肉，也想整点清粥小菜。应该有很多朋友跟我一样，希望有一套简易的状态机实现，每行代码自己都了如指掌，实现我们一些简单的状态控制的需求。In hand，伸手就来的方便！

下面是我的实现，有错误或者low的地方，欢迎大家留言，一起进步吧！

讲到状态机，首当其冲的肯定是状态，我们把状态细分为不同的阶段，每个阶段处理各自的事情。状态里最基本要有OnEnter，OnExit，OnUpdate三个阶段的处理。在 Unity下，我把OnUpdate分得更细，原因在于有些操作需要放在特定的帧下面执行，比如相机的跟随，角色的移动等。

    /// <summary>    /// 状态基类.    /// </summary>    public class FiniteState {        public string Name {            get {                return GetType().Name;            }        }        public virtual void OnEnter(object context){}        public virtual void OnExit(object context){}        public virtual void OnUpdate(object context){}        public virtual void OnFixedUpdate(object context){}        public virtual void OnLateUpdate(object context){}    }}

Transition是有限状态机里面不可或缺的三要素之一，它主要约束状态之间的过渡，A和B两个状态之间是否存在过渡关系，以及过渡的条件是什么，就由FiniteStateTransition来决定。

using UnityEngine;using System.Collections;namespace PLY.StateMachine{    /// <summary>    /// 状态机过渡约束基类.    /// </summary>    public class FiniteStateTransition {        public string EventName;        public string LastStateName;        public string NextStateName;        public FiniteStateTransition(string eventName, string lastStateName, string nextStateName){            EventName = eventName;            LastStateName = lastStateName;            NextStateName = nextStateName;        }    }

最后是管理所有状态及其之间 Transition关系的状态机，它提供映射 Transition的方法，接收触发事件并过渡到对应的状态。

using UnityEngine;using System.Collections;using System.Collections.Generic;namespace PLY.StateMachine {    /// <summary>    /// 有限状态机基类.    /// </summary>    [System.Serializable]    public class FiniteStateMachine : MonoBehaviour {        private object Context_;        public string CurrentStateName = "EmptyState";        private FiniteState CurrentState_;        protected FiniteState CurrentState{            get{                return CurrentState_;            }            set{                CurrentState_ = value;                CurrentStateName = CurrentState_.Name;            }        }        protected FiniteState defaultState;        private Dictionary<string, FiniteState> allStates_ = new Dictionary<string, FiniteState>();        private List<FiniteStateTransition> allTransitions_ = new List<FiniteStateTransition>();        protected virtual void Init(){}        protected void AddState(FiniteState state){            allStates_.Add(state.Name, state);        }        protected void RemoveState(FiniteState state){            allStates_.Remove(state.Name);        }        /// <summary>        /// 添加过渡.        /// </summary>        /// <param name="eventName">Event name.</param>        /// <typeparam name="T1">源状态类型.</typeparam>        /// <typeparam name="T2">目标状态类型.</typeparam>        protected void AddTransition<T1,T2>(string eventName)where T1 : FiniteState where T2 : FiniteState{            string lastStateName = typeof(T1).Name;            string nextStateName = typeof(T2).Name;            FiniteStateTransition transition = new FiniteStateTransition(eventName, lastStateName, nextStateName );            allTransitions_.Add(transition);        }        protected void AddTransition(FiniteStateTransition transition){            allTransitions_.Add(transition);        }        protected void RemoveTransation(FiniteStateTransition transition){            allTransitions_.Remove(transition);        }        public void SetContext(object context){            Context_ = context;        }        /// <summary>        /// 发送事件，触发下一状态的切换        /// </summary>        /// <param name="eventName">事件名.</param>        public void SendEvent(string eventName){            for (int i = 0; i < allTransitions_.Count; i++) {                FiniteState nextState;                if (TryGetNextStateByEventName(allTransitions_[i], eventName, out nextState)){                    ChangeState(nextState);                    break;                }            }        }        private bool TryGetNextStateByEventName(FiniteStateTransition transation, string eventName, out FiniteState state){            state = null;            if (CurrentState == null || !CurrentState.Name.Equals(transation.LastStateName)) return false;            if (!eventName.Equals(transation.EventName)) return false;            return (allStates_.TryGetValue(transation.NextStateName, out state));        }        /// <summary>        /// 切换状态.        /// </summary>        /// <param name="newState">New state.</param>        private void ChangeState(FiniteState newState){            if (CurrentState != null){                CurrentState.OnExit(Context_);            }            else{                Debug.LogError("当前状态为空，退出状态失败！", gameObject);            }            CurrentState = newState;            if(CurrentState != null){                CurrentState.OnEnter(Context_);            }            else{                Debug.LogError("当前状态为空，进入状态失败！", gameObject);            }        }        private void SetDefaultToCurrent(){            CurrentState = defaultState;        }        private void Awake(){            Init();            SetDefaultToCurrent();        }        private void Start () {            if (CurrentState != null){                CurrentState.OnEnter(Context_);            }               }        private void Update () {            if (CurrentState != null){                CurrentState.OnUpdate(Context_);            }        }        private void FixedUpdate(){            if (CurrentState != null){                CurrentState.OnFixedUpdate(Context_);            }        }        private void LateUpdate(){            if (CurrentState != null){                CurrentState.OnLateUpdate(Context_);            }        }    }}

下面是我的测试用例了，简单写了一个关于锁的状态机，两种状态：锁住，未锁住。

using UnityEngine;using System.Collections;using PLY.StateMachine;public class PlayerStateMachine : FiniteStateMachine{    protected override void Init (){        Locked state1 = new Locked();        AddState(state1);        Unlocked state2 = new Unlocked();        AddState(state2);        defaultState = state1;        AddTransition<Locked, Unlocked>("UNLOCK");        AddTransition<Unlocked, Locked>("LOCK");    }}public class Locked : FiniteState{    public override void OnEnter (object target){        Player owner = target as Player;        owner.Show(true);    }    public override void OnExit (object target){}    public override void OnUpdate (object target){}}public class Unlocked : FiniteState{    public override void OnEnter (object target){        Player owner = target as Player;        owner.Show(false);    }    public override void OnExit (object target){}    public override void OnUpdate (object target){}}

using UnityEngine;using System.Collections;using PLY.StateMachine;public class Player : MonoBehaviour{    public FiniteStateMachine StateMachine;    private bool isShowingLockedView_;    private Texture LockTex_;    private Texture UnlockTex_;    private void Awake(){        StateMachine.SetContext(this);        LockTex_ = Resources.Load("tex_locked") as Texture;        UnlockTex_ = Resources.Load("tex_unlocked") as Texture;    }    private void OnGUI(){        if(GUI.Button(new Rect(0,0,120,30), "UNLOCK")){            StateMachine.SendEvent("UNLOCK");        }        if(GUI.Button(new Rect(0,40,120,30), "LOCK")){            StateMachine.SendEvent("LOCK");        }        if(isShowingLockedView_){            GUI.Label(new Rect(Screen.width/2,50,128,128), new GUIContent(LockTex_));        }        else{            GUI.Label(new Rect(Screen.width/2,50,128,128), new GUIContent(UnlockTex_));        }    }    public void Show(bool isLocked){        isShowingLockedView_ = isLocked;    }}