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

 GameData.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
[System.Serializable]
public class GameData
{
    public int currency;
    public SerializableDictionary<string, bool> skillTree;
    public SerializableDictionary<string, int> inventory;
    public List<string> equipmentId;
    public GameData()
    {
        this.currency = 0;
        skillTree = new SerializableDictionary<string, bool>();
        inventory = new SerializableDictionary<string, int>();
        equipmentId = new List<string>();
    }
}

Skill

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

public class Skill : MonoBehaviour
{
    public float cooldown;
    protected float cooldownTimer;

    protected Player player;//拿到player
    
    protected virtual void Start()
    {
        player = PlayerManager.instance.player;//拿到player

        CheckUnlock();
    }
    protected virtual void Update()
    {
        cooldownTimer -= Time.deltaTime;
    }
    protected virtual void CheckUnlock()//再次打开游戏时读取数据文件后使技能可以使用的函数
    {

    }

    public virtual bool CanUseSkill()
    {
        if (cooldownTimer < 0)
        {
            UseSkill();
            cooldownTimer = cooldown;
            return true;
        }
        else
        {
            Debug.Log("Skill is on cooldown");
            return false;
        }

    }
    public virtual void UseSkill()
    {
        // do some skill thing
    }


    //整理能返回最近敌人位置的函数
    protected virtual Transform FindClosestEnemy(Transform _checkTransform)
    {
        Collider2D[] colliders = Physics2D.OverlapCircleAll(_checkTransform.position, 25);//找到环绕自己的所有碰撞器

        float closestDistance = Mathf.Infinity;//正无穷大的表示形式（只读）
        Transform closestEnemy = null;


        //https://docs.unity3d.com/cn/current/ScriptReference/Mathf.Infinity.html
        foreach (var hit in colliders)
        {
            if (hit.GetComponent<Enemy>() != null)
            {
                float distanceToEnemy = Vector2.Distance(_checkTransform.position, hit.transform.position);//拿到与敌人之间的距离
                if (distanceToEnemy < closestDistance)//比较距离，如果离得更近，保存这个敌人的位置,更改最近距离
                {
                    closestDistance = distanceToEnemy;
                    closestEnemy = hit.transform;
                }
            }
        }

        return closestEnemy;
       
    }

}

UI_SkillTreeSlot

using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

public class UI_SkillTreeSlot : MonoBehaviour, IPointerEnterHandler, IPointerExitHandler,ISaveManager
{

    [SerializeField] private int skillCost;
    [SerializeField] private string skillName;
    [TextArea]
    [SerializeField] private string skillDescription;
    [SerializeField] private Color lockedSkillColor;

    private UI ui;

    public bool unlocked;//一个表示是否解锁的bool值

    private Image skillImage;
    [SerializeField] private UI_SkillTreeSlot[] shouldBeUnlocked;
    [SerializeField] private UI_SkillTreeSlot[] shouldBeLocked;//应该解锁和不该解锁的Slot组和Image


    private void OnValidate()
    {
        gameObject.name = "SkillTreeSlot_UI - " + skillName;
        
    }
    private void Awake()
    {
        GetComponent<Button>().onClick.AddListener(() => UnlockSkillSlot());
    }
    private void Start()
    {
        skillImage = GetComponent<Image>();

        skillImage.color = lockedSkillColor;

        ui = GetComponentInParent<UI>();

        if (unlocked)
            skillImage.color = Color.white;
    }

    public void UnlockSkillSlot()//一个判断此Skill是否可以解锁的函数
    {
        if (PlayerManager.instance.HaveEnoughMoney(skillCost) == false)
            return;

        Debug.Log("Slot unlocked");
        for (int i = 0; i < shouldBeUnlocked.Length; i++)
        {
            if (shouldBeUnlocked[i].unlocked == false)
            {
                Debug.Log("Cannot unlock skill");
                return;
            }
        }

        for (int i = 0; i < shouldBeLocked.Length; i++)
        {
            if (shouldBeLocked[i].unlocked == true)
            {
                Debug.Log("Cannot unlock skill");
                return;
            }
        }

        unlocked = true;
        skillImage.color = Color.white;
    }

    public void OnPointerEnter(PointerEventData eventData)
    {
        ui.skillToolTip.ShowToolTip(skillDescription, skillName,skillCost.ToString());
    }

    public void OnPointerExit(PointerEventData eventData)
    {
        ui.skillToolTip.HideToolTip();
    }

    public void LoadData(GameData _data)
    {
        if(_data.skillTree.TryGetValue(skillName,out bool value))
        {
            unlocked = value;
        }
    }

    public void SaveData(ref GameData _data)
    {
        if (_data.skillTree.TryGetValue(skillName, out bool value))//这应该是跟clear一样的，但是为什么不直接用clear？
                                                                   //因为clear会调用24次，每一次都把前面保存的删了，最后只剩下一个
        {
            _data.skillTree.Remove(skillName);
            _data.skillTree.Add(skillName, unlocked);
        }
        else
        {
            _data.skillTree.Add(skillName, unlocked);
        }
        //_data.skillTree.Clear();
        //_data.skillTree.Add(skillName, unlocked);

    }
}

Dogge_Skill

using UnityEngine;
using UnityEngine.UI;

public class Dogge_Skill : Skill
{
    [Header("Dodge")]
    [SerializeField] private UI_SkillTreeSlot unlockDoggeButton;
    [SerializeField] private int evasionAmount;
    public bool doggeUnlocked;

    [Header("Mirage dodge")]
    [SerializeField] private UI_SkillTreeSlot unlockMirageDoggeButton;
    public bool dodgemirageUnlocked;

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

        unlockDoggeButton.GetComponent<Button>().onClick.AddListener(UnlockDodge);
        unlockMirageDoggeButton.GetComponent<Button>().onClick.AddListener(UnlockMirageDogge);
    }
    protected override void CheckUnlock()
    {
        UnlockDodge();
        UnlockMirageDogge();
    }
    private void UnlockDodge()
    {
        if (unlockDoggeButton.unlocked && !doggeUnlocked)
        {
            player.stats.evasion.AddModifier(evasionAmount);
            Inventory.instance.UpdateStatsUI();
            doggeUnlocked = true;

        }
    }
    private void UnlockMirageDogge()
    {
        if (unlockMirageDoggeButton.unlocked)
            dodgemirageUnlocked = true;
    }

    public void CreateMirageOnDoDogge()
    {
        if (dodgemirageUnlocked)
            SkillManager.instance.clone.CreateClone(player.transform, Vector3.zero);
    }
}