C#/基于Unity 行为树的实现步骤【纯代码】

using BTAI;
using UnityEngine;

public class TestBT : MonoBehaviour, BTAI.IBTDebugable
{
    Root aiRoot = BT.Root();


    private void OnEnable()
    {
        aiRoot.OpenBranch(
                BT.If(TestVisibleTarget).OpenBranch(
                BT.Call(Aim),
                BT.Call(Shoot)
                 ),
                BT.Sequence().OpenBranch(
                BT.Call(Walk),
                BT.Wait(5.0f),
                BT.Call(Turn),
                BT.Wait(1.0f),
                BT.Call(Turn)
             )
        );
    }

    private void Turn()
    {
        Debug.Log("执行了 Turn");
    }

    private void Walk()
    {
        Debug.Log("执行了 Walk");
    }

    private void Shoot()
    {
        Debug.Log("执行了 Shoot");
    }

    private void Aim()
    {
        Debug.Log("执行了 Aim");
    }

    private bool TestVisibleTarget()
    {
        var isSuccess = UnityEngine.Random.Range(0, 2) == 1;
        Debug.Log("执行了 TestVisibleTarget    Result:" + isSuccess);

        return isSuccess;
    }

    private void Update()
    {
        aiRoot.Tick();
    }

    public Root GetAIRoot()
    {
        return aiRoot;
    }
}

using System.Collections.Generic;
using UnityEngine;

/// <summary>
/// 这只是脚本系统
/// 行为树会从Root节点开始遍历子节点。Update中执行
/// 每个节点都有相关的操作，但是基本上就是返回三种状态
/// ● Success: 节点成功完成任务
/// ● Failure: 节点未通过任务
/// ● Continue:节点尚未完成任务。
/// 但是每个节点的父节点对子节点的结果处理方式还不同。  例如
/// ● Test 节点： 测试节点将调用其子节点并在测试为真时返回子节点状态，如果测试为假，则返回Failure而不调用其子节点。
/// 行为树的一种构造方式如下：
/// Root aiRoot = BT.Root(); 
/// aiRoot.Do(  
/// BT.If(TestVisibleTarget).Do(
///  BT.Call(Aim),
///  BT.Call(Shoot)
///  ),
///  BT.Sequence().Do(
///  BT.Call(Walk),
///  BT.Wait(5.0f),
///  BT.Call(Turn),
///  BT.Wait(1.0f),
///  BT.Call(Turn)
///  )
/// ); 
///然后在Update中 调用   aiRoot.Tick() 。  刚刚构造的行为树是怎么样的检查过程呢？  
///1、首先检查TestVisibleTarget是否返回Ture，如果是继续执行子节点执行Aim函数和Shoot函数
///2、TestVisibleTarget是否返回false,if节点将返回Failure， 然后Root 将转向下一个子节点。这是个Sequence节点，它从执行第一个子节点开始。
///   1）将调用Walk函数，直接返回 Success，以便Sequence将下一个子节点激活并执行它。
///   2）执行Wait 节点，只是要等待5秒，还是第一次调用，所以肯定返回Running状态， 当Sequence从子节点上得到Running状态时，不会更改激活的子节点索引，下次Update的时候还是从这个节点开始执行
///3、Update的执行，当Wait节点等待的时间到了的时候，将会返回Success， 以便序列将转到下一个孩子。
///脚本中的Node列表 
/// Sequence：
//一个接一个地执行子节点。如果子节点返回：
//●Success：Sequence将选择下一帧的下一个孩子开始。
//●Failure：Sequence将返回到下一帧的第一个子节点（从头开始）。
//●Continue：Sequence将在下一帧再次调用该节点。
//RandomSequence：
// 每次调用时，从子列表中执行一个随机子节点。您可以在构造函数中指定要应用于每个子项的权重列表作为int数组，以使某些子项更有可能被选中。
//Selector ：
//按顺序执行所有子项，直到一个返回Success，然后退出而不执行其余子节点。如果没有返回Success，则此节点将返回Failure。

// Condition ：
// 如果给定函数返回true，则此节点返回Success;如果为false，则返回Failure。
// 与其他依赖于子节点结果的节点链接时很有用（例如，Sequence，Selector等）
// If ：
//调用给定的函数。
// ●如果返回true，则调用当前活动的子级并返回其状态。
// ●否则，它将在不调用其子项的情况下返回Failure
// While：
//只要给定函数返回true，就返回Continue（因此，下一帧将再次从该节点开始，而不会评估所有先前的节点）。
//子节点们将陆续被执行。
//当函数返回false并且循环中断时，将返回Failure。
// Call 
//调用给定的函数，它将始终返回Success。是动作节点！
//Repeat 
//将连续执行给定次数的所有子节点。
//始终返回Continue，直到达到计数，并返回Success。
//Wait
//将返回Continue，直到达到给定时间（首次调用时开始），然后返回Success。
//Trigger 
//允许在给定的动画师animator中设置Trigger参数（如果最后一个参数设置为false，则取消设置触发器）。始终返回成功。
//SetBool
//允许在给定的animator中设置布尔参数的值。始终返回成功
//SetActive 
//设置给定GameObject的活动/非活动状态。始终返回成功。
/// </summary>
namespace BTAI
{
    public enum BTState
    {
        Failure,
        Success,
        Continue,
        Abort
    }

    /// <summary>
    /// 节点 对象工厂
    /// </summary>
    public static class BT
    {
        public static Root Root() { return new Root(); }
        public static Sequence Sequence() { return new Sequence(); }
        public static Selector Selector(bool shuffle = false) { return new Selector(shuffle); }
        public static Action RunCoroutine(System.Func<IEnumerator<BTState>> coroutine) { return new Action(coroutine); }
        public static Action Call(System.Action fn) { return new Action(fn); }
        public static ConditionalBranch If(System.Func<bool> fn) { return new ConditionalBranch(fn); }
        public static While While(System.Func<bool> fn) { return new While(fn); }
        public static Condition Condition(System.Func<bool> fn) { return new Condition(fn); }
        public static Repeat Repeat(int count) { return new Repeat(count); }
        public static Wait Wait(float seconds) { return new Wait(seconds); }
        public static Trigger Trigger(Animator animator, string name, bool set = true) { return new Trigger(animator, name, set); }
        public static WaitForAnimatorState WaitForAnimatorState(Animator animator, string name, int layer = 0) { return new WaitForAnimatorState(animator, name, layer); }
        public static SetBool SetBool(Animator animator, string name, bool value) { return new SetBool(animator, name, value); }
        public static SetActive SetActive(GameObject gameObject, bool active) { return new SetActive(gameObject, active); }
        public static WaitForAnimatorSignal WaitForAnimatorSignal(Animator animator, string name, string state, int layer = 0) { return new WaitForAnimatorSignal(animator, name, state, layer); }
        public static Terminate Terminate() { return new Terminate(); }
        public static Log Log(string msg) { return new Log(msg); }
        public static RandomSequence RandomSequence(int[] weights = null) { return new BTAI.RandomSequence(weights); }

    }

    /// <summary>
    /// 节点抽象类
    /// </summary>
    public abstract class BTNode
    {
        public abstract BTState Tick();
    }

    /// <summary>
    /// 包含子节点的组合 节点基类
    /// </summary>
    public abstract class Branch : BTNode
    {
        protected int activeChild;
        protected List<BTNode> children = new List<BTNode>();
        public virtual Branch OpenBranch(params BTNode[] children)
        {
            for (var i = 0; i < children.Length; i++)
                this.children.Add(children[i]);
            return this;
        }

        public List<BTNode> Children()
        {
            return children;
        }

        public int ActiveChild()
        {
            return activeChild;
        }

        public virtual void ResetChildren()
        {
            activeChild = 0;
            for (var i = 0; i < children.Count; i++)
            {
                Branch b = children[i] as Branch;
                if (b != null)
                {
                    b.ResetChildren();
                }
            }
        }
    }

    /// <summary>
    /// 装饰节点    只包含一个子节点，用于某种方式改变这个节点的行为
    /// 比如过滤器（用于决定是否允许子节点运行的，如：Until Success, Until Fail等），这种节点的子节点应该是条件节点，条件节点一直检测“视线中是否有敌人”，知道发现敌人为止。
    /// 或者 Limit 节点，用于指定某个子节点的最大运行次数
    /// 或者 Timer节点，设置了一个计时器，不会立即执行子节点，而是等一段时间，时间到了开始执行子节点
    /// 或者 TimerLimit节点，用于指定某个子节点的最长运行时间。
    /// 或者 用于产生某个返回状态，
    /// </summary>
    public abstract class Decorator : BTNode
    {
        protected BTNode child;
        public Decorator Do(BTNode child)
        {
            this.child = child;
            return this;
        }
    }

    /// <summary>
    /// 顺序节点 （从左到右依次执行所有子节点，只要子节点返回Success就继续执行后续子节点，直到遇到Failure或者Runing， 
    /// 停止后续执行，并把这个节点返回给父节点，只有它的所有子节点都是Success他才会向父节点返回Success）
    /// </summary>
    public class Sequence : Branch
    {
        public override BTState Tick()
        {
            var childState = children[activeChild].Tick();
            switch (childState)
            {
                case BTState.Success:
                    activeChild++;
                    if (activeChild == children.Count)
                    {
                        activeChild = 0;
                        return BTState.Success;
                    }
                    else
                        return BTState.Continue;
                case BTState.Failure:
                    activeChild = 0;
                    return BTState.Failure;
                case BTState.Continue:
                    return BTState.Continue;
                case BTState.Abort:
                    activeChild = 0;
                    return BTState.Abort;
            }
            throw new System.Exception("This should never happen, but clearly it has.");
        }
    }

    /// <summary>
    /// 选择节点从左到右依次执行所有子节点 ，只要遇到failure就继续执行后续子节点，直到遇到一个节点返回Success或Running为止。向父节点返回Success或Running
    /// 所有子节点都是Fail， 那么向父节点凡湖Fail
    /// 选择节点 用来在可能的行为集合中选择第一个成功的。 比如一个试图躲避枪击的AI角色， 它可以通过寻找隐蔽点， 或离开危险区域， 或寻找援助等多种方式实现目标。
    /// 利用选择节点，他会尝试寻找Cover，失败后在试图逃离危险区域。
    /// </summary>
    public class Selector : Branch
    {
        public Selector(bool shuffle)
        {
            if (shuffle)
            {
                var n = children.Count;
                while (n > 1)
                {
                    n--;
                    var k = Mathf.FloorToInt(Random.value * (n + 1));
                    var value = children[k];
                    children[k] = children[n];
                    children[n] = value;
                }
            }
        }

        public override BTState Tick()
        {
            var childState = children[activeChild].Tick();
            switch (childState)
            {
                case BTState.Success:
                    activeChild = 0;
                    return BTState.Success;
                case BTState.Failure:
                    activeChild++;
                    if (activeChild == children.Count)
                    {
                        activeChild = 0;
                        return BTState.Failure;
                    }
                    else
                        return BTState.Continue;
                case BTState.Continue:
                    return BTState.Continue;
                case BTState.Abort:
                    activeChild = 0;
                    return BTState.Abort;
            }
            throw new System.Exception("This should never happen, but clearly it has.");
        }
    }

    /// <summary>
    /// 行为节点  调用方法，或运行协程。完成实际工作， 例如播放动画，让角色移动位置，感知敌人，更换武器，播放声音，增加生命值等。
    /// </summary>
    public class Action : BTNode
    {
        System.Action fn;
        System.Func<IEnumerator<BTState>> coroutineFactory;
        IEnumerator<BTState> coroutine;
        public Action(System.Action fn)
        {
            this.fn = fn;
        }
        public Action(System.Func<IEnumerator<BTState>> coroutineFactory)
        {
            this.coroutineFactory = coroutineFactory;
        }
        public override BTState Tick()
        {
            if (fn != null)
            {
                fn();
                return BTState.Success;
            }
            else
            {
                if (coroutine == null)
                    coroutine = coroutineFactory();
                if (!coroutine.MoveNext())
                {
                    coroutine = null;
                    return BTState.Success;
                }
                var result = coroutine.Current;
                if (result == BTState.Continue)
                    return BTState.Continue;
                else
                {
                    coroutine = null;
                    return result;
                }
            }
        }

        public override string ToString()
        {
            return "Action : " + fn.Method.ToString();
        }
    }

    /// <summary>
    /// 条件节点   调用方法，如果方法返回true则返回成功，否则返回失败。
    /// 用来测试当前是否满足某些性质或条件，例如“玩家是否在20米之内？”“是否能看到玩家？”“生命值是否大于50？”“弹药是否足够？”等
    /// </summary>
    public class Condition : BTNode
    {
        public System.Func<bool> fn;

        public Condition(System.Func<bool> fn)
        {
            this.fn = fn;
        }
        public override BTState Tick()
        {
            return fn() ? BTState.Success : BTState.Failure;
        }

        public override string ToString()
        {
            return "Condition : " + fn.Method.ToString();
        }
    }

    /// <summary>
    /// 当方法为True的时候 尝试执行当前  子节点
    /// </summary>
    public class ConditionalBranch : Block
    {
        public System.Func<bool> fn;
        bool tested = false;
        public ConditionalBranch(System.Func<bool> fn)
        {
            this.fn = fn;
        }
        public override BTState Tick()
        {
            if (!tested)
            {
                tested = fn();
            }
            if (tested)
            {
                // 当前子节点执行完就进入下一个节点(超上限就返回到第一个)
                var result = base.Tick();
                // 没执行完
                if (result == BTState.Continue)
                    return BTState.Continue;
                else
                {
                    tested = false;
                    // 最后一个子节点执行完，才会为Ture
                    return result;
                }
            }
            else
            {
                return BTState.Failure;
            }
        }

        public override string ToString()
        {
            return "ConditionalBranch : " + fn.Method.ToString();
        }
    }

    /// <summary>
    /// While节点   只要方法  返回True 就执行所有子节点， 否则返回 Failure
    /// </summary>
    public class While : Block
    {
        public System.Func<bool> fn;

        public While(System.Func<bool> fn)
        {
            this.fn = fn;
        }

        public override BTState Tick()
        {
            if (fn())
                base.Tick();
            else
            {
                //if we exit the loop
                ResetChildren();
                return BTState.Failure;
            }

            return BTState.Continue;
        }

        public override string ToString()
        {
            return "While : " + fn.Method.ToString();
        }
    }

    /// <summary>
    /// 阻塞节点  如果当前子节点是Continue 说明没有执行完，阻塞着，执行完之后在继续它后面的兄弟节点 不管成功失败。
    /// 如果当前结点是最后一个节点并执行完毕，说明成功！否则就是处于Continue状态。 
    /// 几个基本上是抽象节点， 像是让所有子节点都执行一遍， 当前子节点执行完就进入下一个节点(超上限就返回到第一个)
    /// </summary>
    public abstract class Block : Branch
    {
        public override BTState Tick()
        {
            switch (children[activeChild].Tick())
            {
                case BTState.Continue:
                    return BTState.Continue;
                default:
                    activeChild++;
                    if (activeChild == children.Count)
                    {
                        activeChild = 0;
                        return BTState.Success;
                    }
                    return BTState.Continue;
            }
        }
    }

    public class Root : Block
    {
        public bool isTerminated = false;

        public override BTState Tick()
        {
            if (isTerminated) return BTState.Abort;
            while (true)
            {
                switch (children[activeChild].Tick())
                {
                    case BTState.Continue:
                        return BTState.Continue;
                    case BTState.Abort:
                        isTerminated = true;
                        return BTState.Abort;
                    default:
                        activeChild++;
                        if (activeChild == children.Count)
                        {
                            activeChild = 0;
                            return BTState.Success;
                        }
                        continue;
                }
            }
        }
    }

    /// <summary>
    /// 多次运行子节点（一个子节点执行一次就算一次）
    /// </summary>
    public class Repeat : Block
    {
        public int count = 1;
        int currentCount = 0;
        public Repeat(int count)
        {
            this.count = count;
        }
        public override BTState Tick()
        {
            if (count > 0 && currentCount < count)
            {
                var result = base.Tick();
                switch (result)
                {
                    case BTState.Continue:
                        return BTState.Continue;
                    default:
                        currentCount++;
                        if (currentCount == count)
                        {
                            currentCount = 0;
                            return BTState.Success;
                        }
                        return BTState.Continue;
                }
            }
            return BTState.Success;
        }

        public override string ToString()
        {
            return "Repeat Until : " + currentCount + " / " + count;
        }
    }


    /// <summary>
    /// 随机的顺序  执行子节点 
    /// </summary>
    public class RandomSequence : Block
    {
        int[] m_Weight = null;
        int[] m_AddedWeight = null;

        /// <summary>
        /// 每次再次触发时，将选择一个随机子节点
        /// </summary>
        /// <param name="weight">保留null，以便所有子节点具有相同的权重。
        /// 如果权重低于子节点， 则后续子节点的权重都为1</param>
        public RandomSequence(int[] weight = null)
        {
            activeChild = -1;

            m_Weight = weight;
        }

        public override Branch OpenBranch(params BTNode[] children)
        {
            m_AddedWeight = new int[children.Length];

            for (int i = 0; i < children.Length; ++i)
            {
                int weight = 0;
                int previousWeight = 0;

                if (m_Weight == null || m_Weight.Length <= i)
                {//如果没有那个权重， 就将权重 设置为1
                    weight = 1;
                }
                else
                    weight = m_Weight[i];

                if (i > 0)
                    previousWeight = m_AddedWeight[i - 1];

                m_AddedWeight[i] = weight + previousWeight;
            }

            return base.OpenBranch(children);
        }

        public override BTState Tick()
        {
            if (activeChild == -1)
                PickNewChild();

            var result = children[activeChild].Tick();

            switch (result)
            {
                case BTState.Continue:
                    return BTState.Continue;
                default:
                    PickNewChild();
                    return result;
            }
        }

        void PickNewChild()
        {
            int choice = Random.Range(0, m_AddedWeight[m_AddedWeight.Length - 1]);

            for (int i = 0; i < m_AddedWeight.Length; ++i)
            {
                if (choice - m_AddedWeight[i] <= 0)
                {
                    activeChild = i;
                    break;
                }
            }
        }

        public override string ToString()
        {
            return "Random Sequence : " + activeChild + "/" + children.Count;
        }
    }


    /// <summary>
    /// 暂停执行几秒钟。
    /// </summary>
    public class Wait : BTNode
    {
        public float seconds = 0;
        float future = -1;
        public Wait(float seconds)
        {
            this.seconds = seconds;
        }

        public override BTState Tick()
        {
            if (future < 0)
                future = Time.time + seconds;

            if (Time.time >= future)
            {
                future = -1;
                return BTState.Success;
            }
            else
                return BTState.Continue;
        }

        public override string ToString()
        {
            return "Wait : " + (future - Time.time) + " / " + seconds;
        }
    }

    /// <summary>
    /// 设置动画  trigger 参数
    /// </summary>
    public class Trigger : BTNode
    {
        Animator animator;
        int id;
        string triggerName;
        bool set = true;

        //如果 set == false, 则重置trigger而不是设置它。
        public Trigger(Animator animator, string name, bool set = true)
        {
            this.id = Animator.StringToHash(name);
            this.animator = animator;
            this.triggerName = name;
            this.set = set;
        }

        public override BTState Tick()
        {
            if (set)
                animator.SetTrigger(id);
            else
                animator.ResetTrigger(id);

            return BTState.Success;
        }

        public override string ToString()
        {
            return "Trigger : " + triggerName;
        }
    }

    /// <summary>
    /// 设置动画 boolean 参数
    /// </summary>
    public class SetBool : BTNode
    {
        Animator animator;
        int id;
        bool value;
        string triggerName;

        public SetBool(Animator animator, string name, bool value)
        {
            this.id = Animator.StringToHash(name);
            this.animator = animator;
            this.value = value;
            this.triggerName = name;
        }

        public override BTState Tick()
        {
            animator.SetBool(id, value);
            return BTState.Success;
        }

        public override string ToString()
        {
            return "SetBool : " + triggerName + " = " + value.ToString();
        }
    }

    /// <summary>
    /// 等待animator达到一个状态。
    /// </summary>
    public class WaitForAnimatorState : BTNode
    {
        Animator animator;
        int id;
        int layer;
        string stateName;

        public WaitForAnimatorState(Animator animator, string name, int layer = 0)
        {
            this.id = Animator.StringToHash(name);
            if (!animator.HasState(layer, this.id))
            {
                Debug.LogError("The animator does not have state: " + name);
            }
            this.animator = animator;
            this.layer = layer;
            this.stateName = name;
        }

        public override BTState Tick()
        {
            var state = animator.GetCurrentAnimatorStateInfo(layer);
            if (state.fullPathHash == this.id || state.shortNameHash == this.id)
                return BTState.Success;
            return BTState.Continue;
        }

        public override string ToString()
        {
            return "Wait For State : " + stateName;
        }
    }

    /// <summary>
    /// 设置 GameObject 的激活状态
    /// </summary>
    public class SetActive : BTNode
    {

        GameObject gameObject;
        bool active;

        public SetActive(GameObject gameObject, bool active)
        {
            this.gameObject = gameObject;
            this.active = active;
        }

        public override BTState Tick()
        {
            gameObject.SetActive(this.active);
            return BTState.Success;
        }

        public override string ToString()
        {
            return "Set Active : " + gameObject.name + " = " + active;
        }
    }

    /// <summary>
    /// 等待animator从SendSignal状态机行为 接收信号。   SendSignal : StateMachineBehaviour
    /// </summary>
    public class WaitForAnimatorSignal : BTNode
    {
        // 进入或退出动画都为 False， 只有执行中为True
        internal bool isSet = false;
        string name;
        int id;

        public WaitForAnimatorSignal(Animator animator, string name, string state, int layer = 0)
        {
            this.name = name;
            this.id = Animator.StringToHash(name);
            if (!animator.HasState(layer, this.id))
            {
                Debug.LogError("The animator does not have state: " + name);
            }
            else
            {
                SendSignal.Register(animator, name, this);
            }
        }

        public override BTState Tick()
        {
            if (!isSet)
                return BTState.Continue;
            else
            {
                isSet = false;
                return BTState.Success;
            }

        }

        public override string ToString()
        {
            return "Wait For Animator Signal : " + name;
        }
    }

    /// <summary>
    /// 终止节点  切换到中止 状态
    /// </summary>
    public class Terminate : BTNode
    {

        public override BTState Tick()
        {
            return BTState.Abort;
        }

    }

    /// <summary>
    /// Log  输出Log 的节点
    /// </summary>
    public class Log : BTNode
    {
        string msg;

        public Log(string msg)
        {
            this.msg = msg;
        }

        public override BTState Tick()
        {
            Debug.Log(msg);
            return BTState.Success;
        }
    }

}

#if UNITY_EDITOR
namespace BTAI
{
    public interface IBTDebugable
    {
        Root GetAIRoot();
    }
}
#endif

using BTAI;
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

namespace Gamekit2D
{

    /// <summary>
    /// 运行是查看  行为树中所有节点的状态 
    /// </summary>
    public class BTDebug : EditorWindow
    {
        protected BTAI.Root _currentRoot = null;


        [MenuItem("Kit Tools/Behaviour Tree Debug")]
        static void OpenWindow()
        {
            BTDebug btdebug = GetWindow<BTDebug>();
            btdebug.Show();
        }

        private void OnGUI()
        {
            if (!Application.isPlaying)
            {
                EditorGUILayout.HelpBox("Only work during play mode.", MessageType.Info);
            }
            else
            {
                if (_currentRoot == null)
                    FindRoot();
                else
                {
                    RecursiveTreeParsing(_currentRoot, 0, true);
                }
            }
        }

        void Update()
        {
            Repaint();
        }

        void RecursiveTreeParsing(Branch branch, int indent, bool parentIsActive)
        {
            List<BTNode> nodes = branch.Children();

            for (int i = 0; i < nodes.Count; ++i)
            {
                EditorGUI.indentLevel = indent;

                bool isActiveChild = branch.ActiveChild() == i;
                GUI.color = (isActiveChild && parentIsActive) ? Color.green : Color.white;
                EditorGUILayout.LabelField(nodes[i].ToString());

                if (nodes[i] is Branch)
                    RecursiveTreeParsing(nodes[i] as Branch, indent + 1, isActiveChild);
            }
        }

        void FindRoot()
        {
            if (Selection.activeGameObject == null)
            {
                _currentRoot = null;
                return;
            }

            IBTDebugable debugable = Selection.activeGameObject.GetComponentInChildren<IBTDebugable>();

            if (debugable != null)
            {
                _currentRoot = debugable.GetAIRoot();
            }
        }

    }
}