在Unity中玩转表达式树：解锁游戏逻辑的动态魔法

 

 

using System;

using System.Linq.Expressions;

using System.Reflection;

using UnityEngine;

using Object = UnityEngine.Object;

public class EnemyStateMachine : MonoBehaviour {

    //定义状态机委托，以Enemy和Hero为参数，返回一个以Enemy和Hero为参数的空方法

    //它会根据英雄的状态（如生命值和距离）返回一个相应的行为函数。

    Func<Enemy, Hero, Action<Enemy, Hero>> stateEvaluator;

    //存储当前行为函数

    Action<Enemy, Hero> behavior;

    Enemy enemy;

    Hero hero;

    void Start() {

        enemy = FindObjectOfType<Enemy>();

        hero = FindObjectOfType<Hero>();

        stateEvaluator = CreateDynamicStateMachine();

    }

    void Update() {

        //获取当前行为

        behavior = stateEvaluator(enemy, hero);

        //执行当前行为

        behavior(enemy, hero);

        Debug.Log("Enemy Aggression Level:", enemy.AggressionLevel);

    }

    public Func<Enemy, Hero, Action<Enemy, Hero>> CreateDynamicStateMachine() {

        //定义参数表达式

        ParameterExpression enemyParam = Expression.Parameter(typeof(Enemy), "enemy");

        ParameterExpression heroParam = Expression.Parameter(typeof(Hero), "hero");

        //定义一个二元表达式

        BinaryExpression heroLowHealth = Expression.LessThan(

            Expression.Property(heroParam, "Health"),

            Expression.Constant(30)

        );

        BinaryExpression heroNear = Expression.LessThan(

            Expression.Property(heroParam, "Distance"),

            Expression.Constant(10f)

        );

        Debug.Log($"HeroLowHealth{heroLowHealth}");

        Debug.Log($"HeroNear{heroNear}");

        var attack = CreateActionExpression("Attack").Compile();

        var taunt = CreateActionExpression("Taunt").Compile();

        var patrol = CreateActionExpression("Patrol").Compile();

        //条件表达式，如果heroNear为真则执行taunt，否则执行patrol

        ConditionalExpression tauntOrPatrol = Expression.Condition(heroNear, Expression.Constant(taunt), Expression.Constant(patrol));

        ConditionalExpression finalCondition = Expression.Condition(heroLowHealth, Expression.Constant(attack), tauntOrPatrol);

        //

        var lambda = Expression.Lambda<Func<Enemy, Hero, Action<Enemy, Hero>>>(finalCondition, enemyParam, heroParam);

        return lambda.Compile();

    }

    Expression<Action<Enemy, Hero>> CreateActionExpression(string methodName) {

        ParameterExpression enemyParam = Expression.Parameter(typeof(Enemy), "enemy");

        ParameterExpression heroParam = Expression.Parameter(typeof(Hero), "hero");

        MethodInfo method = typeof(Enemy).GetMethod(methodName, new[] { typeof(Hero) });

        MethodCallExpression call = Expression.Call(enemyParam, method, heroParam);

        return Expression.Lambda<Action<Enemy, Hero>>(call, enemyParam, heroParam);

    }

}