Saving and loading

In plain English

PlayerPrefs is a simple key-value store for small preferences, but it is not built for large or structured save data. JSON is a text format for describing objects, and JsonUtility turns a plain C# class into a JSON string and back. Application.persistentDataPath is a per-app folder that persists across sessions and is the right place for save files. Versioning a save means storing a version number in the file so you can migrate old saves when the format changes.

Step by step

1. 1Define a serializable data class for the save.
2. 2Serialize it to JSON with JsonUtility.
3. 3Write the JSON to Application.persistentDataPath.
4. 4Load the file back and deserialize it with FromJson.
5. 5Add a version field so future changes can migrate.

using System.IO;
using UnityEngine;

[System.Serializable]
public class SaveData
{
    public int score;
    public float version = 1f;
}

public class SaveSystem : MonoBehaviour
{
    private string SavePath => Path.Combine(Application.persistentDataPath, "save.json");

    public void Save(SaveData data)
    {
        string json = JsonUtility.ToJson(data);
        File.WriteAllText(SavePath, json);
    }

    public SaveData Load()
    {
        if (!File.Exists(SavePath)) return new SaveData();
        string json = File.ReadAllText(SavePath);
        return JsonUtility.FromJson<SaveData>(json);
    }
}

Common mistakes

• Storing a whole save game in PlayerPrefs bloats the registry and slows loading; keep it for small preferences.
• Saving to a hardcoded relative path works in the editor but fails on a device, where the game cannot write arbitrary folders.
• Changing the shape of a save without a version number makes old saves crash or load garbage.
• JsonUtility only serializes public or SerializeField fields, so private fields silently disappear from the save.