Question JsonUtility.ToJson produces blank JSON even for int data

I am trying to build a simple system for saving my game state to a JSON file, but I keep getting blank JSON. I have read many posts on this forum and on Stack Overflow from people with similar issues, but in all of the issues I have seen, the issue boiled down to the player trying to serialize a complex type (e.g. a Dictionary) that Unity's JsonUtility cannot serialize. But I am getting blank JSON even with primitive types, e.g. integers.

Here is a minimal example:

1. Create an empty 3D project and generate two C# scripts as follows:

GameData.cs, a class for holding the data:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. [System.Serializable]using System.Collections;
6. using System.Collections.Generic;
7. using UnityEngine;
8.  
9. [System.Serializable]
10. public class GameData
11. {
12.     public int score { get; set; }
13.     public int health { get; set; }
14.  
15.     public GameData(int score, int health)
16.     {
17.         this.score = score;
18.         this.health = health;
19.     }
20. }
21.  

SaveLoadManager.cs, which will write the JSON to a file (in this case, we just write to the console to keep things simple):

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class SaveLoadManager : MonoBehaviour
6. {
7.     void OnMouseDown()
8.     {
9.         SaveJson();
10.     }
11.  
12.     void SaveJson()
13.     {
14.         var data = new GameData(4, 5);
15.         var serializedData = JsonUtility.ToJson(data);
16.         Debug.Log($"Serialized data: {serializedData}");
17.     }
18. }
19.  
20.  

2. Create an empty cube and add the SaveLoadManager.cs script to it.

3. Play the game and click on the cube. The following is logged to the console:



("Serialized data: {}")

Why is my JSON empty?

(Unity v2021.3.16f1 on Windows 10.)

 

JsonUtility doesn't serialize properties, only fields that are either public or have the SerializeField attribute.

You can tell it to serialize a property's backing field by using

[field: SerializeField]

but it'll be called something like

<score>k__BackingField

in the result.

 

https://docs.unity3d.com/ScriptReference/JsonUtility.ToJson.html

I always use Json.net myself, but one thing I noticed is JsonUtility seems to use fields and not properties. I don't know if there is a difference, but I suggest giving it a try and see if it makes a difference or not.

 

Thank you, I had also read about this issue but got the concepts of fields and properties reversed in my head.