Alex教程每一P的教程原代码加上我自己的理解初步理解写的注释，可供学习Alex教程的人参考
此代码仅为较上一P有所改变的代码

【Unity教程】从0编程制作类银河恶魔城游戏_哔哩哔哩_bilibili

Enemy.cs

using System.Collections;
using System.Collections.Generic;
using Unity.VisualScripting;
using UnityEngine;

public class Enemy : Entity
{
    [SerializeField] protected LayerMask whatIsPlayer;
    [Header("Move Info")]
    public float moveSpeed;
    public float idleTime;
    [Header("Attack Info")]
    public float attackDistance;
    #region 类
    public EnemyStateMachine stateMachine;
    
    #endregion

    protected override void Awake()
    {
        base.Awake();
        stateMachine = new EnemyStateMachine();
        
    }
    protected override void Start()
    {
        base.Start();
       
    }


    protected override void Update()
    {
        base.Update();

        stateMachine.currentState.Update();
        
        //Debug.Log(IsPlayerDetected().collider.gameObject.name + "I see");//这串代码会报错，可能使版本的物体，因为在没有找到Player的时候物体是空的，NULL，你想让他在控制台上显示就报错了
    }

    public virtual RaycastHit2D IsPlayerDetected() => Physics2D.Raycast(wallCheck.position, Vector2.right * facingDir, 50, whatIsPlayer);//用于从射线投射获取信息的结构。
    //该函数的返回值可以变，可以只返回bool，也可以是碰到的结构

    protected override void OnDrawGizmos()
    {
        base.OnDrawGizmos();

        Gizmos.color = Color.yellow;
        Gizmos.DrawLine(transform.position, new Vector3(transform.position.x + attackDistance * facingDir, transform.position.y));
    }
}

Enemy_Skeleton.cs

using System.Collections;
using System.Collections.Generic;
using Unity.VisualScripting;
using UnityEditorInternal;
using UnityEngine;

public class Enemy_Skeleton : Enemy
{
    #region 类State
    public SkeletonIdleState idleState { get; private set; }
    public SkeletonMoveState moveState { get; private set; }
    public SkeletonBattleState battleState { get; private set; }
    #endregion
    protected override void Awake()
    {
        base.Awake();

        idleState = new SkeletonIdleState(this, stateMachine, "Idle", this);
        moveState = new SkeletonMoveState(this,stateMachine, "Move", this);
        battleState = new SkeletonBattleState(this, stateMachine, "Move", this);

    }

    protected override void Start()
    {
        base.Start();
        stateMachine.Initialize(idleState);
    }

    protected override void Update()
    {
        base.Update();
        
    }
}

EnemyState.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class EnemyState
{

    protected Enemy enemyBase;

    protected EnemyStateMachine stateMachine;

    protected Rigidbody2D rb;//小简化

    protected bool triggerCalled;

    private string animBoolName;

    protected float stateTimer;


    public EnemyState(Enemy _enemyBase, EnemyStateMachine _stateMachine, string _animBoolName)
    {
        this.enemyBase = _enemyBase;
        this.stateMachine = _stateMachine;
        this.animBoolName = _animBoolName;
    }
    public virtual void Enter()
    {
        triggerCalled = false;
        enemyBase.anim.SetBool(animBoolName, true);
        rb = enemyBase.rb;//小简化
    }
    public virtual void Update()
    {
        stateTimer -= Time.deltaTime;
    }
    public virtual void Exit()
    {
        enemyBase.anim.SetBool(animBoolName, false);
    }

    
}

SkeletonGroundState.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SkeletonGroundState : EnemyState
{
    protected Enemy_Skeleton enemy;
    public SkeletonGroundState(Enemy _enemyBase, EnemyStateMachine _stateMachine, string _animBoolName,Enemy_Skeleton _enemy) : base(_enemyBase, _stateMachine, _animBoolName)
    {
        enemy = _enemy;
    }

    public override void Enter()
    {
        base.Enter();
    }

    public override void Exit()
    {
        base.Exit();
    }

    public override void Update()
    {
        base.Update();

        if(enemy.IsPlayerDetected())
        {
            stateMachine.ChangeState(enemy.battleState);
        }
    }
}

SkeletonIdleState.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SkeletonIdleState : SkeletonGroundState
{
    public SkeletonIdleState(Enemy _enemyBase, EnemyStateMachine _stateMachine, string _animBoolName, Enemy_Skeleton _enemy) : base(_enemyBase, _stateMachine, _animBoolName, _enemy)
    {
    }

    public override void Enter()
    {
        base.Enter();
        stateTimer = enemy.idleTime;
    }

    public override void Exit()
    {
        base.Exit();
    }

    public override void Update()
    {
        base.Update();
        if(stateTimer < 0)
        {
            stateMachine.ChangeState(enemy.moveState);
        }
    }
}

SkeletonMoveState.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SkeletonMoveState : SkeletonGroundState
{
    public SkeletonMoveState(Enemy _enemyBase, EnemyStateMachine _stateMachine, string _animBoolName, Enemy_Skeleton _enemy) : base(_enemyBase, _stateMachine, _animBoolName, _enemy)
    {
    }

    public override void Enter()
    {
        base.Enter();
    }

    public override void Exit()
    {
        base.Exit();
    }

    public override void Update()
    {
        base.Update();

        enemy.SetVelocity(enemy.moveSpeed * enemy.facingDir, rb.velocity.y);

        if(enemy.IsWallDetected()||!enemy.IsGroundDetected())//当撞墙或者没有路的时候翻转
        {
            enemy.Flip();
            stateMachine.ChangeState(enemy.idleState);
        }
    }
}

SkeletonBattleState.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SkeletonBattleState : EnemyState
{
    private Transform player;//用于给Player定位，好判断怎么跟上他
    private Enemy_Skeleton enemy;
    private int moveDir;
    public SkeletonBattleState(Enemy _enemyBase, EnemyStateMachine _stateMachine, string _animBoolName,Enemy_Skeleton _enemy ) : base(_enemyBase, _stateMachine, _animBoolName)
    {
        enemy = _enemy;
    }

    public override void Enter()
    {
        base.Enter();
        
        player = GameObject.Find("Player").transform;//全局找Player位置
    }

    public override void Exit()
    {
        base.Exit();
    }

    public override void Update()
    {
        base.Update();
        if(enemy.IsPlayerDetected().distance < enemy.attackDistance)
        {
            Debug.Log("I Attack");
            enemy.ZeroVelocity();
            return;
        }
        if(player.position.x > enemy.transform.position.x)
        {
            moveDir = 1;
        }
        else if(player.position.x<enemy.transform.position.x)
        {
            moveDir = -1;
        }

        enemy.SetVelocity(enemy.moveSpeed * moveDir, rb.velocity.y);
    }
}