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

 FileDataHandler.cs

using System;
using System.IO;
using UnityEngine;
public class FileDataHandler
{
    private string dataDirPath = "";
    private string dataFileName = "";

    public FileDataHandler(string _dataDirPath, string _dataFilePath)//构造函数拿到需要保存的位置和文件名称
    {
        dataDirPath = _dataDirPath;
        dataFileName = _dataFilePath;
    }

    public void Save(GameData _data)
    {
        string fullPath = Path.Combine(dataDirPath, dataFileName);//合成路径函数 将位置和文件合并成实际的可以读取的路径

        try//用try防止其报错
        {
            Directory.CreateDirectory(Path.GetDirectoryName(fullPath));//通过路径创建出需要的文件，存在就不创建了
            string dataToStore = JsonUtility.ToJson(_data, true);//将传过来的gameData转换成文本形式并且使其可读

            using (FileStream stream = new FileStream(fullPath, FileMode.Create))//两个using 第一个进入文件使其变为可编写模式
            {
                using (StreamWriter writer = new StreamWriter(stream))//第二个拿到文件对其进行编辑
                {
                    writer.Write(dataToStore);//写入函数
                }
            }

        }

        catch (Exception e)
        {
            Debug.LogError("Error on trying to save data to file " + fullPath + "\n" + e);
        }
    }
    public GameData Load()//同上
    {
        string fullPath = Path.Combine(dataDirPath, dataFileName);
        GameData loadData = null;

        if (File.Exists(fullPath))
        {
            try
            {
                string dataToLoad = "";

                using (FileStream stream = new FileStream(fullPath, FileMode.Open))
                {
                    using (StreamReader reader = new StreamReader(stream))
                    {
                        dataToLoad = reader.ReadToEnd();
                    }
                }

                loadData = JsonUtility.FromJson<GameData>(dataToLoad);//转换为游戏需要的类型
            }
            catch (Exception e)
            {
                Debug.LogError(e);

            }
        }
        return loadData;
    }
}

ISaveManager.cs

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

public interface ISaveManager
{
    void LoadData(GameData _data);
    void SaveData(ref GameData _data);
}

SaveManager.cs

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


public class SaveManager : MonoBehaviour
{
    public static SaveManager instance;
    [SerializeField] private string fileName;
    GameData gameData;
    private List<ISaveManager> saveManagers;
    private FileDataHandler dataHandler;
    private void Awake()
    {
        if (instance != null)
            Destroy(instance);
        else
            instance = this;
    }

    private void Start()
    {
        dataHandler = new FileDataHandler(Application.persistentDataPath, fileName);
        saveManagers = FindAllSaveManagers();

        LoadGame();
    }

    public void NewGame()
    {
        gameData = new GameData();
    }

    public void LoadGame()
    {
        gameData = dataHandler.Load();

        if(this.gameData == null)
        {
            Debug.Log("No data");
            NewGame();
        }

        foreach(ISaveManager saveManager in saveManagers)//循环调用所有的找到脚本的LoadData和SaveData到，这样便可以将所有的数据汇聚到gameData中，并从中拿到data
        {
            saveManager.LoadData(gameData);
        }

        Debug.Log("Loaded currency " + gameData.currency);
    }

    public void SaveGame()循环调用所有的找到脚本的LoadData和SaveData到，这样便可以将所有的数据汇聚到gameData中，并从中拿到data
    {

        foreach(ISaveManager saveManager in saveManagers)
        {
            saveManager.SaveData(ref gameData);
        }

        dataHandler.Save(gameData);
    }

    private void OnApplicationQuit()
    {
        SaveGame();
    }


    private List<ISaveManager> FindAllSaveManagers()//全局寻找带ISave的脚本的函数
    {
        IEnumerable<ISaveManager> saveManager = FindObjectsOfType<MonoBehaviour>().OfType<ISaveManager>();
        
        return new List<ISaveManager>(saveManager);
    }
}

GameData.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
[System.Serializable]
public class GameData
{
    public int currency;

    public GameData()
    {
        this.currency = 0;
    }
}

PlayerManager.cs

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

public class PlayerManager : MonoBehaviour, ISaveManager
{
    public static PlayerManager instance;
    public Player player;//这是通过在外部设置了一个组件，让这个组件能够直接把Player找到，从而减少FInd的方式所带来的高负载

    public int currency;
    private void Awake()
    {
        if(instance != null)
        {
            Destroy(instance.gameObject);
        }
        else
        instance = this;
    }

    public bool HaveEnoughMoney(int _price)
    {
        if(_price > currency)
        {
            Debug.Log("Not enough money");
            return false;
        }

        currency -= _price;
        return true;
    }

    public int GetCurrency() => currency;

    public void LoadData(GameData _data)
    {
        currency = _data.currency;
    }

    public void SaveData(ref GameData _data)
    {
        _data.currency = this.currency;
    }
}