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

ItemData_Equipment.cs

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

public enum EquipmentType
{
    Weapon,
    Armor,
    Amulet,
    Flask

}

[CreateAssetMenu(fileName = "New Item Data", menuName = "Data/Equipment")]
public class ItemData_equipment : ItemData
{
    public EquipmentType equipmentType;

    [Header("Major stats")]
    public int strength; // 力量 增伤1点 爆伤增加 1% 物抗
    public int agility;// 敏捷 闪避 1% 闪避几率增加 1%
    public int intelligence;// 1 点 魔法伤害 1点魔抗 
    public int vitality;//加血的

    [Header("Offensive stats")]
    public int damage;
    public int critChance;      // 暴击率
    public int critPower;       //150% 爆伤

    [Header("Defensive stats")]
    public int maxHealth;
    public int armor;
    public int evasion;//闪避值
    public int magicResistance;

    [Header("Magic stats")]
    public int fireDamage;
    public int iceDamage;
    public int lightingDamage;

    public void AddModifiers()
    {
        PlayerStat playerStats = PlayerManager.instance.player.GetComponent<PlayerStat>();
        playerStats.strength.AddModifier(strength);
        playerStats.agility.AddModifier(agility);
        playerStats.intelligence.AddModifier(intelligence);
        playerStats.vitality.AddModifier(vitality);

        playerStats.damage.AddModifier(damage);
        playerStats.critChance.AddModifier(critChance);
        playerStats.critPower.AddModifier(critPower);

        playerStats.maxHealth.AddModifier(maxHealth);
        playerStats.armor.AddModifier(armor);
        playerStats.evasion.AddModifier(evasion);
        playerStats.magicResistance.AddModifier(magicResistance);

        playerStats.fireDamage.AddModifier(fireDamage);
        playerStats.iceDamage.AddModifier(iceDamage);
        playerStats.lightingDamage.AddModifier(lightingDamage);
    }

    public void RemoveModifiers()
    {
        PlayerStat playerStats = PlayerManager.instance.player.GetComponent<PlayerStat>();
        playerStats.strength.RemoveModifier(strength);
        playerStats.agility.RemoveModifier(agility);
        playerStats.intelligence.RemoveModifier(intelligence);
        playerStats.vitality.RemoveModifier(vitality);

        playerStats.damage.RemoveModifier(damage);
        playerStats.critChance.RemoveModifier(critChance);
        playerStats.critPower.RemoveModifier(critPower);

        playerStats.maxHealth.RemoveModifier(maxHealth);
        playerStats.armor.RemoveModifier(armor);
        playerStats.evasion.RemoveModifier(evasion);
        playerStats.magicResistance.RemoveModifier(magicResistance);

        playerStats.fireDamage.RemoveModifier(fireDamage);
        playerStats.iceDamage.RemoveModifier(iceDamage);
        playerStats.lightingDamage.RemoveModifier(lightingDamage);

    }
}

Inventory.cs

using Newtonsoft.Json.Linq;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Inventory : MonoBehaviour
{
    public static Inventory instance;

    public List<InventoryItem> equipment;//inventoryItems类型的列表
    public Dictionary<ItemData_equipment, InventoryItem> equipmentDictionary;//以ItemData为Key寻找InventoryItem的字典

    public List<InventoryItem> inventory;//inventoryItems类型的列表
    public Dictionary<ItemData, InventoryItem> inventoryDictionary;//以ItemData为Key寻找InventoryItem的字典

    public List<InventoryItem> stash;
    public Dictionary<ItemData, InventoryItem> stashDictionary;

    [Header("Inventory UI")]

    [SerializeField] private Transform inventorySlotParent;
    [SerializeField] private Transform stashSlotParent;
    [SerializeField] private Transform equipmentSlotParent;


    private UI_itemSlot[] inventoryItemSlot;//UI Slot的数组
    private UI_itemSlot[] stashItemSlot;
    private UI_equipementSlots[] equipmentSlot;



    private void Awake()
    {
        if (instance == null)
            instance = this;
        else
            Destroy(gameObject);
        //防止多次创建Inventory
    }

    public void Start()
    {
        inventory = new List<InventoryItem>();
        inventoryDictionary = new Dictionary<ItemData, InventoryItem>();


        stash = new List<InventoryItem>();
        stashDictionary = new Dictionary<ItemData, InventoryItem>();

        equipment = new List<InventoryItem>();
        equipmentDictionary = new Dictionary<ItemData_equipment, InventoryItem>();


        inventoryItemSlot = inventorySlotParent.GetComponentsInChildren<UI_itemSlot>();//拿到的方式有点绕，显示拿到Canvas 里的 Inventory 然后通过GetComponentsInChildren拿到其下的使用UISlot
        stashItemSlot = stashSlotParent.GetComponentsInChildren<UI_itemSlot>();
        equipmentSlot = equipmentSlotParent.GetComponentsInChildren<UI_equipementSlots>();
    }

    public void EquipItem(ItemData _item)
    {
        //解决在itemdata里拿不到子类equipment里的enum的问题
        ItemData_equipment newEquipment = _item as ItemData_equipment;//https://www.bilibili.com/read/cv15551811/
        //将父类转换为子类
        InventoryItem newItem = new InventoryItem(newEquipment);

        ItemData_equipment oldEquipment = null;

        foreach (KeyValuePair<ItemData_equipment, InventoryItem> item in equipmentDictionary)//这种方法可以同时拿到key和value保存到item里面
        {
            if (item.Key.equipmentType == newEquipment.equipmentType)//将拿到的key与转换成itemdata_equipment类型的_item的type对比拿到存在的key
            {
                oldEquipment = item.Key;//此key需保存在外部的data类型里
                //equipment.Remove(item.Value);
                //equipmentDictionary.Remove(item.Key);
            }
        }//好像用foreach里的value和key无法对外部的list和字典进行操作

        if (oldEquipment != null)
        {
            Unequipment(oldEquipment);
            AddItem(oldEquipment);
        }
            

        equipment.Add(newItem);
        equipmentDictionary.Add(newEquipment, newItem);
        newEquipment.AddModifiers();
        RemoveItem(_item);
    }

    private void Unequipment(ItemData_equipment itemToRemove)//装备其他同类型的装备时。去除已装备的装备
    {
        if (equipmentDictionary.TryGetValue(itemToRemove, out InventoryItem value))
        {

            equipment.Remove(value);
            equipmentDictionary.Remove(itemToRemove);
            itemToRemove.RemoveModifiers();
        }
    }

    private void UpdateSlotUI()
    {
        for (int i = 0; i < equipmentSlot.Length; i++)
        {
            //此步骤用于将对应类型的武器插入对应的槽内
            foreach (KeyValuePair<ItemData_equipment, InventoryItem> item in equipmentDictionary)//这种方法可以同时拿到key和value保存到item里面
            {
                if (item.Key.equipmentType == equipmentSlot[i].slotType)
                {
                    equipmentSlot[i].UpdateSlots(item.Value);
                }
            }

        }
        //解决出现UI没有跟着Inventory变化的bug
        for (int i = 0; i < inventoryItemSlot.Length;i++)
        {
            inventoryItemSlot[i].CleanUpSlot();
        }
        for (int i = 0; i < stashItemSlot.Length; i++)
        {
            stashItemSlot[i].CleanUpSlot();
        }

        for (int i = 0; i < inventory.Count; i++)
        {
            inventoryItemSlot[i].UpdateSlots(inventory[i]);
        }

        for (int i = 0; i < stash.Count; i++)
        {
            stashItemSlot[i].UpdateSlots(stash[i]);
        }
    }

    public void AddItem(ItemData _item)
    {
        if (_item.itemType == ItemType.Equipment)
        {
            AddToInventory(_item);
        }
        else if (_item.itemType == ItemType.Material)
        {
            AddToStash(_item);
        }


        UpdateSlotUI();
    }//添加物体的函数

    private void AddToStash(ItemData _item)//向stash加物体的函数
    {
        if (stashDictionary.TryGetValue(_item, out InventoryItem value))//只有这种方法才能在查找到是否存在key对应value是否存在的同时，能够同时拿到value，其他方法的拿不到value
        {
            value.AddStack();
        }//字典的使用，通过ItemData类型的数据找到InventoryItem里的与之对应的同样类型的数据
        else//初始时由于没有相同类型的物体，故调用else是为了初始化库存，使其中含有一个基本的值
        {
            InventoryItem newItem = new InventoryItem(_item);
            stash.Add(newItem);//填进列表里只有一次
            stashDictionary.Add(_item, newItem);//同上
        }
    }

    private void AddToInventory(ItemData _item)
    {
        if (inventoryDictionary.TryGetValue(_item, out InventoryItem value))//只有这种方法才能在查找到是否存在key对应value是否存在的同时，能够同时拿到value，其他方法的拿不到value
        {
            value.AddStack();
        }//字典的使用，通过ItemData类型的数据找到InventoryItem里的与之对应的同样类型的数据
        else//初始时由于没有相同类型的物体，故调用else是为了初始化库存，使其中含有一个基本的值
        {
            InventoryItem newItem = new InventoryItem(_item);
            inventory.Add(newItem);//填进列表里只有一次
            inventoryDictionary.Add(_item, newItem);//同上
        }
    }//将物体存入Inventory的函数

    public void RemoveItem(ItemData _item)//将物体剔除Inventory的函数
    {
        if (inventoryDictionary.TryGetValue(_item, out InventoryItem value))
        {
            if (value.stackSize <= 1)
            {
                inventory.Remove(value);
                inventoryDictionary.Remove(_item);

            }
            else
                value.RemoveStack();
        }

        if (stashDictionary.TryGetValue(_item, out InventoryItem stashValue))
        {
            if (stashValue.stackSize <= 1)
            {
                stash.Remove(value);
                stashDictionary.Remove(_item);

            }
            else
                stashValue.RemoveStack();
        }

        UpdateSlotUI();
    }
}