0
\$\begingroup\$

I try to save game data in PlayerPrefs as JSON string. I read in documentation that I can use plain struct/class with [Serializable] attribute but it doesn't work...

First I thought that data didn't arrive so I start to debug and watch values and saw that data is arrived. Then thought that (may be) SetString method is asynchronous, but when I evaluate the expression JsonUtility.ToJson(GameData) it showed me empty string again

Also I tried:

  • add [SerializeField] to both fields
  • use int instead of enum
  • add/remove [Serializable] attribute for enum

Code editor screenshot showing x is null

The problems disappears when I don't use Nullable fields. Is there any workaround to use Nullable fields?

using System;
using UnityEngine;

[Serializable]
public enum FPSValues {
    High = 60,
    Low = 30
}

[Serializable]
public struct GameData {
    public FPSValues? FPS;
    public bool? IsAudioEnabled;
}

public class GameDataManager : MonoBehaviour {
    public static GameData GameData;

    private void Awake() {
        Load();
    }
    
    public static void Save() {
        PlayerPrefs.SetString("GameData", JsonUtility.ToJson(GameData));
        var x = PlayerPrefs.GetString("GameData");
    }

    private void Load() {
        var x = JsonUtility.FromJson<GameData>(PlayerPrefs.GetString("GameData"));
        GameData = x;
    }
}
```
\$\endgroup\$
2
  • \$\begingroup\$ You said that "remove "?" symbol" did not fix the problem, but that seems to be contradicted by "The problems disappears when I don't use Nullable fields." - do you need to amend the list of things you tried based on this observation? \$\endgroup\$ Commented Dec 7, 2022 at 18:14
  • \$\begingroup\$ @DMGregory I removed only for one field, I thought it would work for this field but it didn't work. Now I tried to remove from both of fields and it works. BTW I can remove this point from list if it is confusing \$\endgroup\$ Commented Dec 7, 2022 at 21:10

2 Answers 2

Reset to default
1
\$\begingroup\$

You can gain the effect of the nullable just by updating your enums:

[System.Serializable]
public enum FPSValues : byte {
    Unset = 0,
    High = 60,
    Low = 30,
}

[System.Serializable]
public enum OptionalBool : byte {
    Unset,
    False,
    True
}

Now instead of if (FPS != null) ... you'd write if (FPS != FPSValues.Unset) ... and the rest is pretty much the same as working with your unmodified enums.

In fact, it even lets you handle all three cases in a single switch:

switch (FPS) {
    case FPSValues.Low: /*...*/ break;
    case FPSValues.High: /*...*/ break;
    default: /*...*/ break;
}

While with a nullable you'd need to write the slightly more cumbersome:

if (FPS.HasValue) {
   switch (FPS.Value) {
       case FPSValues.Low: /*...*/ break;
       case FPSValues.High: /*...*/ break;
   }
} else {
   /* Default behaviour... */
}

This plays nicely with the Unity serializer for both JSON and Inspector parameters (the same logic is used for both, so a good way to check whether a type is supported is to see if you can edit it in the Inspector).

And as a bonus: it uses less memory! The previous nullable versions used 2-8 bytes each (due to adding separate storage for the null flag, plus alignment), while these new enums fit in just a single byte.

\$\endgroup\$
7
  • \$\begingroup\$ Thank you! Yeah I read some solutions which are more or less look like your method. But it is good for small data, imagine that in future I will store more complex data where fields can be also complex structs. It was just basic data to show my problem. Anyway thank you for your advice and trick about byte for enums I didn't know it \$\endgroup\$ Commented Dec 7, 2022 at 22:44
  • \$\begingroup\$ If you have more complex data structures that need to be optional, it may be worth making them class type instead of struct. Then you can use [SerializeReference] to store a null, or implement custom serialization/deserialization callbacks if you need bespoke behaviour. \$\endgroup\$ Commented Dec 7, 2022 at 22:46
  • \$\begingroup\$ I already tried it to use class instead of struct and use [SerializeReference] for fields after reading this but it also doesn't work RESULT \$\endgroup\$ Commented Dec 7, 2022 at 22:56
  • \$\begingroup\$ You've misunderstood. class is not a keyword that you put on a container that magically makes nullable struct members inside it serializable now. Nullable structs are not serializable using Unity's serializer. Full stop. [SerializeReference] is useful if you have a member that is a class type (not a nullable struct), and you want it to be able to be serialized as null rather than as a default instance. \$\endgroup\$ Commented Dec 7, 2022 at 23:10
  • 1
    \$\begingroup\$ public class Foo { public int a; } public class Bar { public Foo foo; } By default, when you serialize Bar and then deserialize it, foo will contain a non-null instance with foo.a = 0. If you put [SerializeReference] Foo foo then when you deserialize it, foo will be null, rather than an instance with default values. \$\endgroup\$ Commented Dec 7, 2022 at 23:57
1
\$\begingroup\$

There is nothing wrong with your code. x is null in your example because that line of code did not yet get executed. If you add another line after it, you will see that x will be of type GameData.

public static void Save() {
    PlayerPrefs.SetString("GameData", JsonUtility.ToJson(GameData));
    var x = PlayerPrefs.GetString("GameData");
    Debug.Log(x);
}

To make your code read easier, don't name the variable the exactly the same as your class/ struct, enum. Use _ or different case to make sure when you mean the variable and when the class.

\$\endgroup\$
1
  • \$\begingroup\$ Thank you! But it is not a problem. I wrote x because I got empty string when evaluate JsonUtility.ToJson(GameData). As far as I understood this is due to what I use Nullable fields in struct. Because when I remove them it works. Are Nullable fields not allowed to serialize? \$\endgroup\$ Commented Dec 7, 2022 at 16:51

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.