Class Persistence in Unity

Games need to store some persistent data like high scores and progress between the game sessions. Fortunately Unity gives us PlayerPrefs class that is essentially a persistent hash map.

Reading and writing values with PlayerPrefs is as simple as calling get and set.

// saving data
PlayerPrefs.SetInt("foobar", 10);
PlayerPrefs.SetString("something", "foo");
PlayerPrefs.Save();
...
// reading data
if(PlayerPrefs.HasKey("foobar")) {
    int foo = PlayerPrefs.GetInt("foobar");
}

It has its limitations, only strings and numbers can be stored and that makes more complex data lot more difficult to maintain.

What we can do is to write simple utility that can be used to serialize classes to strings that can then be read and written with PlayerPrefs. SerializerUtil is static class with two methods to Load and Write object. In case loading fails it returns default value of the data, usually null.

using System;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

public static class SerializerUtil {
	static BinaryFormatter bf = new BinaryFormatter ();
	
	public static T LoadObject<T>(string key)
	{
		if (!PlayerPrefs.HasKey(key))
			return default(T);
		
		try {	
			string tmp = PlayerPrefs.GetString(key);
			MemoryStream dataStream = new MemoryStream(Convert.FromBase64String(tmp));
			return (T)bf.Deserialize(dataStream);
			
		} catch (Exception e) {
			Debug.Log("Failed to read "+ key+ " err:" + e.Message);
			return default(T);
		}				
	}
	
	public static void SaveObject<T>(string key, T dataObject)
	{
		MemoryStream memoryStream = new MemoryStream ();
		bf.Serialize (memoryStream, dataObject);
		string tmp = Convert.ToBase64String (memoryStream.ToArray ());
		PlayerPrefs.SetString ( key, tmp);
	}
}

To load and save your classes, declare them as Serializable.

[Serializable]
public class PlayerData {
	public int points;
	public string name; 		
}

You can then easily store instances of the class.

var data = new PlayerData();
data.points = 50;
data.name = "Teemu";

SerializerUtil.SaveObject("player1", data);

Reading classes is also simple

PlayerData data;
data = SerializerUtil.LoadObject<PlayerData>("player1");
// data.points is 50
// data.name is "Teemu"

Classes can be also more complicated, you can add member functions and also exclude some member variables from serialization. It’s also possible to define member function that will be called after serialization, it’s good way to init class after deserialization from disk.

[Serializable]
public class PlayerData : IDeserializationCallback {
	public int points;
	public string name;
    
	// serialization ignores this member variable
	[NonSerialized] Dictionary<int, int> progress = new Dictionary<int, int>();

	// constructor is called only on new instances
	public PlayerData() {
		points = 0;
		name = "Anon";
	}
	
	// serializable class can have member methods as usual
	public bool ValidName() 
	{
		return name.Trim().Length > 4; 
	}

	// Called only on deserialized classes
	void IDeserializationCallback.OnDeserialization(System.Object sender) 
	{
	    // do your init stuff here
	    progress = new Dictionary<int, int>();	
	}
}

Caveats

This serialization does not support versioning. You can not read the stored instance anymore if you change the class members as the LoadObject will fail to deserialize the data.

You need to add following environment variable to force Mono runtime to use reflection instead JIT. Otherwise the serialization will fail on iOS devices. Do this before doing any loading or saving of classes.

void Awake() {
    Environment.SetEnvironmentVariable("MONO_REFLECTION_SERIALIZER", "yes");
    ...

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