[JsonUtility] cannot deserialize json to new instances of type X

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Hi, so i'm trying to create a "PlayerStats" object using the JsonUtility class. There are no errors in the Editor but whenever i run the code i get the Exception : System.ArgumentException: Cannot deserialize JSON to new instances of type 'PlayerStats.' and i don't know why. I use the method just like they do in the documentation but i keep getting that exception. The json file was created using JU.ToJson and should work without problem. What am i missing ?

             if (File.Exists(savePath + "\\" + name + ".json")) {
                 string saveData = File.ReadAllText(savePath + "\\" + name + ".json");
                 GameObject localPlayer = (GameObject)Instantiate(Resources.Load("Player/" +                                                              JsonUtility.FromJson<PlayerStats>(saveData).race.ToString()));
             }

the json file :

 {
     "race": 0,
     "playerName": "xxx",
     "initative": 10.0
 }

PlayerStats.cs :

 public class PlayerStats : MonoBehaviour {
     public Race race;
     public string playerName;
 
     public float initative = 10;
     // Use this for initialization
     void Start () {
         
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 }

Answer 1

Best Answer

Answer by Bunny83 · Feb 04, 2017 at 03:56 PM

"PlayerStats" should not be a MonoBehaviour. The JsonUtility can only be used for data classes. MonoBehaviours are components which need to be attached to gameobjects. You can't simply "create" an instance, that's why it failed.

Try:

 [System.Serializable]
 public class PlayerStats
 {
     public Race race;
     public string playerName;
     
     public float initative = 10;
 }

Of course this class can not be attached to a gameobject. It's only ment as a data class that represents your save data. Also note that the "Race" class also can't be a MonoBehaviour. All classes you want to save / restore have to be normal serializable classes (or maybe derived from ScriptableObject, though i never used that JsonUtility myself).

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Bunny83 · Feb 04, 2017 at 03:59 PM 0

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ps: by looking at your json data it looks like your "race" is actually a number. I doubt that it can create a "Race" instance from a number. Have you created that Json data yourself?

huialx Bunny83 · Feb 04, 2017 at 04:51 PM 0

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"Race" is just an enum and the json was created using JasonUtility.ToJson(). I see, eventhough it's strange i can create multiple PlayerStats object from within the PlayerStats script. I have created my own Jsonparser for my use-case but i will keep it in $$anonymous$$d incase i use JsonUtility in the future. Thanks.

DSivtsov · Feb 18 at 03:47 PM 0

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Not fully correct answer watch below answer @gz7190

Answer 2

Answer by gz7190 · Aug 28, 2019 at 05:52 PM

In case anyone else comes across this and still wants to serialize MonoBehaviour or ScriptableObject, the fine print in the docs state the following:

However, when deserializing JSON into subclasses of MonoBehaviour or ScriptableObject, you must use FromJsonOverwrite; FromJson is not supported and will throw an exception.

source: https://docs.unity3d.com/Manual/JSONSerialization.html

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unity-marcus · Feb 18, 2020 at 10:25 AM 0

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Thanks for pointing this out, this finally solved my problem deserializing a ScriptableObject from JSON!

[JsonUtility] cannot deserialize json to new instances of type X

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