Unity Basic Course: Save and Load Functions, Using JSON

1. Introduction

The ability to save and retrieve player progress, settings, or other important data in game development is very important.
Unity provides various methods to easily implement these features.
In this tutorial, we will take a closer look at how to save and load data in Unity using JSON (JavaScript Object Notation) format.

2. What is JSON?

JSON is a lightweight format for exchanging data, based on JavaScript object notation.
Data is organized in key-value pairs, making it easy to read for humans and easy for machines to parse.
When using JSON in Unity, data structures can be easily serialized to save to a file and deserialized back into objects when loading.

3. Example of a JSON Object

The basic structure of JSON format is as follows:

{
    "name": "Player1",
    "score": 100,
    "level": 2,
    "items": ["sword", "shield", "potion"]
}

The example above is a JSON object that contains information related to a game character.
This structure can be easily managed through serialization and deserialization in Unity.

4. Using JSON in Unity

To use JSON functionality in Unity, you can utilize the JsonUtility class.
This class provides methods to easily convert JSON data into objects and vice versa.
Below is how to create a JSON object and serialize it to save it to a file.

4.1 Defining the Data Structure

Define the class structure for the data you want to save.
For example, let’s create a class to hold player information.

[System.Serializable]
public class PlayerData {
    public string name;
    public int score;
    public int level;
    public List<string> items;
}

The above class includes the player’s name, score, level, and item list.
The [System.Serializable] attribute was added so that it can be serialized to JSON.

4.2 JSON Serialization and File Saving

Let’s write code to serialize data to JSON and save it to a file.
The System.IO namespace makes file input and output easy.

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

public class GameManager : MonoBehaviour {
    private string savePath;

    void Start() {
        savePath = Path.Combine(Application.persistentDataPath, "playerData.json");
    }

    public void SavePlayerData(PlayerData playerData) {
        string jsonData = JsonUtility.ToJson(playerData);
        File.WriteAllText(savePath, jsonData);
    }
}

In the above code, the SavePlayerData method converts player data to JSON format and saves it to a file at the specified path.
You can obtain the appropriate file path for each platform using Application.persistentDataPath.

4.3 Loading JSON Files

Loading a saved JSON file is also straightforward.
The code below shows the process of reading JSON data from a file and deserializing it into a PlayerData object.

public PlayerData LoadPlayerData() {
    if (File.Exists(savePath)) {
        string jsonData = File.ReadAllText(savePath);
        PlayerData playerData = JsonUtility.FromJson<PlayerData>(jsonData);
        return playerData;
    }
    return null;
}

LoadPlayerData checks if the saved file exists, then reads the file and converts the JSON data into a PlayerData object.

5. Example Code

The example below demonstrates the overall save and load process.
It shows how to implement data saving and loading through button clicks in Unity.

using UnityEngine;
using UnityEngine.UI;
using System.Collections.Generic;
using System.IO;

public class GameManager : MonoBehaviour {
    public InputField nameInput;
    public Slider scoreSlider;
    public Button saveButton;
    public Button loadButton;

    private string savePath;

    void Start() {
        savePath = Path.Combine(Application.persistentDataPath, "playerData.json");
        
        saveButton.onClick.AddListener(OnSaveButtonClick);
        loadButton.onClick.AddListener(OnLoadButtonClick);
    }

    public void OnSaveButtonClick() {
        PlayerData playerData = new PlayerData {
            name = nameInput.text,
            score = (int)scoreSlider.value,
            level = 1,
            items = new List<string> { "sword", "shield" }
        };
        SavePlayerData(playerData);
    }

    public void OnLoadButtonClick() {
        PlayerData loadedData = LoadPlayerData();
        if (loadedData != null) {
            nameInput.text = loadedData.name;
            scoreSlider.value = loadedData.score;
        }
    }

    public void SavePlayerData(PlayerData playerData) {
        string jsonData = JsonUtility.ToJson(playerData);
        File.WriteAllText(savePath, jsonData);
    }

    public PlayerData LoadPlayerData() {
        if (File.Exists(savePath)) {
            string jsonData = File.ReadAllText(savePath);
            PlayerData playerData = JsonUtility.FromJson<PlayerData>(jsonData);
            return playerData;
        }
        return null;
    }
}

The above code implements the functionality to save the user’s input data (name and score) and to load the saved data to display it in the UI.
Each method is invoked through button click events.

6. Importance of Save and Load Functionality

The save and load functionality is essential for enhancing user experience.
Without this feature, players would lose all their progress every time they exit the game, which could diminish the enjoyment of the game.
Therefore, designing an appropriate data storage structure and effectively managing file I/O is very important for game developers.

7. Conclusion

In this tutorial, we explored how to save and load data in Unity using JSON.
JSON is a simple yet powerful data format that can be used in various applications.
With this foundational knowledge, you will be able to build more complex data storage logic or repositories.

I hope this information on advanced Unity tutorials and related topics will continue to be helpful for you in the future.
Thank you!