What is the best way to save game state?

I know this post is old, but in case other users also find it while searching for save strategies, remember:

PlayerPrefs is not for storing game state. It is explicitly named "PlayerPrefs" to indicate its use: storing player preferences. It is essentially plain text. It can easily be located, opened, and edited by any player. This may not be a concern for all developers, but it will matter to many whose games are competitive.

Use PlayerPrefs for Options menu settings like volume sliders and graphics settings: things where you don't care that the player can set and change them at will.

Use I/O and serialization for saving game data, or send it to a server as Json. These methods are more secure than PlayerPrefs, even if you encrypt the data before saving.

But I heard this way has some issues and not suitable for save.

That's right. On some devices, there are issues with BinaryFormatter. It gets worse when you update or change the class. Your old settings might be lost since the classes non longer match. Sometimes, you get an exception when reading the saved data due to this.

Also, on iOS, you have to add Environment.SetEnvironmentVariable("MONO_REFLECTION_SERIALIZER", "yes"); or you will have problems with BinaryFormatter.

The best way to save is with PlayerPrefs and Json. You can learn how to do that here.

In my case, save format must be byte array

In this case, you can convert it to json then convert the json string to byte array. You can then use File.WriteAllBytes and File.ReadAllBytes to save and read the byte array.

Here is a Generic class that can be used to save data. Almost the-same as this but it does not use PlayerPrefs. It uses file to save the json data.

DataSaver class:

public class DataSaver
{
    //Save Data
    public static void saveData<T>(T dataToSave, string dataFileName)
    {
        string tempPath = Path.Combine(Application.persistentDataPath, "data");
        tempPath = Path.Combine(tempPath, dataFileName + ".txt");

        //Convert To Json then to bytes
        string jsonData = JsonUtility.ToJson(dataToSave, true);
        byte[] jsonByte = Encoding.ASCII.GetBytes(jsonData);

        //Create Directory if it does not exist
        if (!Directory.Exists(Path.GetDirectoryName(tempPath)))
        {
            Directory.CreateDirectory(Path.GetDirectoryName(tempPath));
        }
        //Debug.Log(path);

        try
        {
            File.WriteAllBytes(tempPath, jsonByte);
            Debug.Log("Saved Data to: " + tempPath.Replace("/", "\\"));
        }
        catch (Exception e)
        {
            Debug.LogWarning("Failed To PlayerInfo Data to: " + tempPath.Replace("/", "\\"));
            Debug.LogWarning("Error: " + e.Message);
        }
    }

    //Load Data
    public static T loadData<T>(string dataFileName)
    {
        string tempPath = Path.Combine(Application.persistentDataPath, "data");
        tempPath = Path.Combine(tempPath, dataFileName + ".txt");

        //Exit if Directory or File does not exist
        if (!Directory.Exists(Path.GetDirectoryName(tempPath)))
        {
            Debug.LogWarning("Directory does not exist");
            return default(T);
        }

        if (!File.Exists(tempPath))
        {
            Debug.Log("File does not exist");
            return default(T);
        }

        //Load saved Json
        byte[] jsonByte = null;
        try
        {
            jsonByte = File.ReadAllBytes(tempPath);
            Debug.Log("Loaded Data from: " + tempPath.Replace("/", "\\"));
        }
        catch (Exception e)
        {
            Debug.LogWarning("Failed To Load Data from: " + tempPath.Replace("/", "\\"));
            Debug.LogWarning("Error: " + e.Message);
        }

        //Convert to json string
        string jsonData = Encoding.ASCII.GetString(jsonByte);

        //Convert to Object
        object resultValue = JsonUtility.FromJson<T>(jsonData);
        return (T)Convert.ChangeType(resultValue, typeof(T));
    }

    public static bool deleteData(string dataFileName)
    {
        bool success = false;

        //Load Data
        string tempPath = Path.Combine(Application.persistentDataPath, "data");
        tempPath = Path.Combine(tempPath, dataFileName + ".txt");

        //Exit if Directory or File does not exist
        if (!Directory.Exists(Path.GetDirectoryName(tempPath)))
        {
            Debug.LogWarning("Directory does not exist");
            return false;
        }

        if (!File.Exists(tempPath))
        {
            Debug.Log("File does not exist");
            return false;
        }

        try
        {
            File.Delete(tempPath);
            Debug.Log("Data deleted from: " + tempPath.Replace("/", "\\"));
            success = true;
        }
        catch (Exception e)
        {
            Debug.LogWarning("Failed To Delete Data: " + e.Message);
        }

        return success;
    }
}

USAGE:

Example class to Save:

[Serializable]
public class PlayerInfo
{
    public List<int> ID = new List<int>();
    public List<int> Amounts = new List<int>();
    public int life = 0;
    public float highScore = 0;
}

Save Data:

PlayerInfo saveData = new PlayerInfo();
saveData.life = 99;
saveData.highScore = 40;

//Save data from PlayerInfo to a file named players
DataSaver.saveData(saveData, "players");

Load Data:

PlayerInfo loadedData = DataSaver.loadData<PlayerInfo>("players");
if (loadedData == null)
{
    return;
}

//Display loaded Data
Debug.Log("Life: " + loadedData.life);
Debug.Log("High Score: " + loadedData.highScore);

for (int i = 0; i < loadedData.ID.Count; i++)
{
    Debug.Log("ID: " + loadedData.ID[i]);
}
for (int i = 0; i < loadedData.Amounts.Count; i++)
{
    Debug.Log("Amounts: " + loadedData.Amounts[i]);
}

Delete Data:

DataSaver.deleteData("players");