Unity 策略模式（实例详解）

简介

在Unity中使用策略模式，我们可以将不同的行为或算法封装成独立的类（策略），然后根据需要在运行时动态选择和切换这些策略。下面我将通过5个简化的代码示例来说明如何在Unity中实现策略模式。

示例1：角色攻击行为

// 定义策略接口（抽象策略类）
public abstract class AttackStrategy
{
    public abstract void ExecuteAttack(Character target);
}

// 具体策略类 - 近战攻击
public class MeleeAttack : AttackStrategy
{
    public override void ExecuteAttack(Character target)
    {
        Debug.Log($"{target.name} 使用近战攻击了 {target.Target.name}");
        // 实现具体的近战攻击逻辑...
    }
}

// 具体策略类 - 远程攻击
public class RangedAttack : AttackStrategy
{
    public override void ExecuteAttack(Character target)
    {
        Debug.Log($"{target.name} 发射了一枚远程攻击向 {target.Target.name}");
        // 实现具体的远程攻击逻辑...
    }
}

// 上下文类 - 角色
public class Character
{
    public AttackStrategy CurrentAttackStrategy { get; set; }

    public void ChangeAttackStrategy(AttackStrategy newStrategy)
    {
        CurrentAttackStrategy = newStrategy;
    }

    public void PerformAttack()
    {
        if (CurrentAttackStrategy != null)
        {
            CurrentAttackStrategy.ExecuteAttack(this);
        }
    }
}

// 使用示例
Character player = new Character();
player.CurrentAttackStrategy = new MeleeAttack(); // 设置初始攻击策略为近战
player.PerformAttack();

// 游戏进程中动态切换策略
player.ChangeAttackStrategy(new RangedAttack());
player.PerformAttack();

示例2：游戏内购折扣策略

// 抽象折扣策略
public abstract class DiscountStrategy
{
    public abstract float CalculateDiscount(float originalPrice);
}

// 具体折扣策略 - 普通价格
public class NormalDiscount : DiscountStrategy
{
    public override float CalculateDiscount(float originalPrice)
    {
        return originalPrice; // 不打折
    }
}

// 具体折扣策略 - 五折优惠
public class HalfOffDiscount : DiscountStrategy
{
    public override float CalculateDiscount(float originalPrice)
    {
        return originalPrice * 0.5f;
    }
}

// 上下文类 - 购物车
public class ShoppingCart
{
    public DiscountStrategy CurrentDiscountStrategy { get; set; }

    public float GetFinalPrice(float itemPrice)
    {
        return itemPrice * CurrentDiscountStrategy.CalculateDiscount(itemPrice);
    }

    public void SetDiscountStrategy(DiscountStrategy newDiscount)
    {
        CurrentDiscountStrategy = newDiscount;
    }
}

// 使用示例
ShoppingCart cart = new ShoppingCart();
cart.CurrentDiscountStrategy = new NormalDiscount();
float finalPrice = cart.GetFinalPrice(100); // 原价购买

cart.SetDiscountStrategy(new HalfOffDiscount());
finalPrice = cart.GetFinalPrice(100); // 半价购买

示例3：NPC寻路策略

// 抽象寻路策略
public abstract class PathfindingStrategy
{
    public abstract List<Vector3> FindPath(Vector3 start, Vector3 end);
}

// 具体寻路策略 - A*寻路
public class AStarPathfinding : PathfindingStrategy
{
    public override List<Vector3> FindPath(Vector3 start, Vector3 end)
    {
        // 实现A*算法寻找路径
        // ...
        return pathList;
    }
}

// 具体寻路策略 - Dijkstra寻路
public class DijkstraPathfinding : PathfindingStrategy
{
    public override List<Vector3> FindPath(Vector3 start, Vector3 end)
    {
        // 实现Dijkstra算法寻找路径
        // ...
        return pathList;
    }
}

// 上下文类 - NPC实体
public class NPC
{
    public PathfindingStrategy CurrentPathfindingStrategy { get; set; }

    public void MoveTo(Vector3 destination)
    {
        var path = CurrentPathfindingStrategy.FindPath(transform.position, destination);
        // 根据路径移动NPC
        // ...
    }

    public void SetPathfindingStrategy(PathfindingStrategy newPathfinding)
    {
        CurrentPathfindingStrategy = newPathfinding;
    }
}

// 使用示例
NPC npc = new NPC();
npc.CurrentPathfindingStrategy = new AStarPathfinding();
npc.MoveTo(targetPosition);

// 更改寻路策略
npc.SetPathfindingStrategy(new DijkstraPathfinding());
npc.MoveTo(anotherTargetPosition);

示例4：动画过渡策略

// 抽象动画过渡策略
public abstract class TransitionStrategy
{
    public abstract void ApplyTransition(Animator animator, string targetState);
}

// 具体动画过渡策略 - 直接切换
public class DirectTransition : TransitionStrategy
{
    public override void ApplyTransition(Animator animator, string targetState)
    {
        animator.CrossFade(targetState, 0f);
    }
}

// 具体动画过渡策略 - 平滑过渡
public class SmoothTransition : TransitionStrategy
{
    public override void ApplyTransition(Animator animator, string targetState)
    {
        animator.CrossFade(targetState, 0.5f);
    }
}

// 上下文类 - 动画控制器
public class AnimationController
{
    public TransitionStrategy CurrentTransitionStrategy { get; set; }

    public void ChangeAnimation(string stateName)
    {
        CurrentTransitionStrategy.ApplyTransition(animator, stateName);
    }

    public void SetTransitionStrategy(TransitionStrategy newStrategy)
    {
        CurrentTransitionStrategy = newStrategy;
    }
}

// 使用示例
AnimationController animCtrl = new AnimationController();
animCtrl.CurrentTransitionStrategy = new DirectTransition();
animCtrl.ChangeAnimation("Run");

// 更改过渡策略
animCtrl.SetTransitionStrategy(new SmoothTransition());
animCtrl.ChangeAnimation("Idle");

示例5：敌人AI决策策略

// 抽象AI决策策略
public abstract class AIActionStrategy
{
    public abstract void DecideAction(Enemy enemy);
}

// 具体AI决策策略 - 随机行动
public class RandomAI : AIActionStrategy
{
    public override void DecideAction(Enemy enemy)
    {
        int randomChoice = Random.Range(0, 3);
        switch (randomChoice)
        {
            case 0:
                enemy.Attack();
                break;
            case 1:
                enemy.Defend();
                break;
            case 2:
                enemy.Flee();
                break;
        }
    }
}

// 具体AI决策策略 - 精确计算行动
public class CalculatedAI : AIActionStrategy
{
    public override void DecideAction(Enemy enemy)
    {
        // 根据战场情况、玩家状态等精确计算并执行动作
        // ...
    }
}

// 上下文类 - 敌人实体
public class Enemy
{
    public AIActionStrategy CurrentAIAction { get; set; }

    public void UpdateAI()
    {
        CurrentAIAction.DecideAction(this);
    }

    public void SetAIAction(AIActionStrategy newAI)
    {
        CurrentAIAction = newAI;
    }
}

// 使用示例
Enemy enemy = new Enemy();
enemy.CurrentAIAction = new RandomAI();
enemy.UpdateAI(); // 随机执行动作

// 更改AI策略
enemy.SetAIAction(new CalculatedAI());
enemy.UpdateAI(); // 根据计算结果执行动作

以上每个示例都展示了策略模式的基本应用，在Unity中可以根据具体项目需求灵活运用这一设计模式。

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