JsonUtilities.ToJson with List<string> not working as expected

Hi guys,

I'm trying to serialize a list using JsonUtilities.ToJson, however I'm running into a problem

When I do the above, the string that it returns is just " {} "

I don't understand why it's returning object, as far as I am aware, ToJson should serialize lists no problem.

My code looks like this

//My list of type string

public List<string> saveList = new List<string>();



//First converting my data to a string. This is serialized correctly, and is as expected

string newStringToSave = JsonUtility.ToJson(Data);



//Add string to list

saveList.Add(newStringToSave);



//Returns {}

string result = JsonUtility.ToJson(saveList);

Anyone have any ideas what could be going wrong here?

EDIT:
I've also tried wrapping the string in a custom class with the Serializable attribute and then add that to the list. Still no luck. Honestly can't figure out where I'm going wrong

 

Alas the Unity JSON utility cannot do this. See here: https://docs.unity3d.com/Manual/JSONSerialization.html

I quote from the above:

"The JSON Serializer does not currently support working with ‘unstructured’ JSON (i.e. navigating and editing the JSON as an arbitrary tree of key-value pairs). If you need to do this, you should look for a more fully-featured JSON library."

Countless developer hours have been squandered discovering this completely unobvious limitation. The Unity JSON "implementation" should never have been named anything but "LITE" or "Primitive" in its title, since everybody naturally expects generic collections would be serialized.

Instead I recommend checking out the Newtonsoft JSON package available for free on the Unity asset store:

https://assetstore.unity.com/packages/tools/input-management/json-net-for-unity-11347

Sorry you were the latest time-waste victim. :/

 

Ah I see. Haha only lost a few hours. More than enough though!. Thanks Kurt. Will take a look at this library now!

 

Thanks for recommending the package. It's excellent. Reverting my code back to what I originally thought would work and sure enough no problems!

 

So if i had a monobehaviour class containing several Lists<> of different custom types that i wrote (and added Serializable to) and attempted to write that whole class to json with Kurt's recommended utility it would work?

i guess im a bit confused by this:

"Note: GameObjects and MonoBehaviors cannot be serialized directly as well as some built in classes (such as Texture2D that doesn't have a public parameterless constructor) but they are simple to serialize using either proxy classes or creating a custom ContractResolver or JsonConverter. JSON .NET is super extensible."

but if i stick all this stuff in a custom class im good right?

I have lots of custom classes that mix Unity stuff like Sprites with my classes and i'm wondering where its gunna break.

 

No sense wondering, you can test.

You will not be able to serialize references to Unity things like Sprites, generally speaking.

When loading, you can never re-create a MonoBehaviour or ScriptableObject instance directly from JSON. The reason is they are hybrid C# and native engine objects, and when the JSON package calls

new

to make one, it cannot make the native engine portion of the object.

Instead you must first create the MonoBehaviour using AddComponent<T>() on a GameObject instance, or use ScriptableObject.CreateInstance<T>() to make your SO, then use the appropriate JSON "populate object" call to fill in its public fields.

Some more Load/Save notes and steps:

https://forum.unity.com/threads/save-system-questions.930366/#post-6087384

Don't use the binary formatter/serializer: it is insecure, it cannot be made secure, and it makes debugging very difficult, plus it actually will NOT prevent people from modifying your save data on their computers.

https://docs.microsoft.com/en-us/dotnet/standard/serialization/binaryformatter-security-guide

 

well for the references like prefabs, textures, sprites i can use [ignorejson] because i store all my refs as strings and load with addressables. Do you know if a serializing nested lists (class with a list of lists of lists) is possible?

 

...

If a rando on the forum says 'yes' or 'no' and is incorrect, has anyone benefitted?

Test!

 

Example code for anyone who don't want to add extra asset. I will add extra level of data, so if you will need multiple objects or list you could still handle it. I hope it will help.

Code (CSharp):

1.  
2.  [System.Serializable]
3.  public class JSONWithListOfObjects
4.  {
5.         public string Date;
6.         public List<CustomObject> spaceList;
7.  }
8.  
9.  
10. [System.Serializable]
11.     public class CustomObject: ICloneable
12.     {
13.         public int Data1;
14.         public string Data2;
15.         public string Data3;
16.  
17.         public object Clone()
18.         {
19.             CustomObject space = new CustomObject
20.             {
21.                 Data1= Data1,
22.                 Data2= Data2,
23.                 Data3= Data3
24.             };
25.             return space;
26.         }
27.     }

This is description of your object of save. Clone() is just used to clone data instead of link, so if data is changed frequently, it wouldn't be effected.

Code (CSharp):

1.          
2. //lets create some random data
3.             for (int i = 0; i < 10; i++) {
4.             CustomObject SomeRandomList = new CustomObject() {
5.                 Data1= i,
6.                 Data2="looool" + i,
7.                 Data3= "target" + i,
8.             };
9. //lets just create new object that we want to save as JSON
10.             JSONWithListOfObjects writeObjectListJSON = new JSONWithListOfObjects();
11. //lets add current time, for extra data
12.             writeObjectListJSON.Date = DateTime.Now.ToString();
13. //now lets put our random data list into our object we will print, next to data.
14.             writeObjectListJSON.spaceList = new List<CustomObject>(SomeRandomList);
15. //create string from the object
16.             string writeToFile = JsonUtility.ToJson(writeObjectListJSON);
17. //you can do whatever after, but for checking lets create file.
18.             File.WriteAllText(Application.dataPath + "/MyJsonFile.json", writeToFile);
19.  

in the end you will get you string in form something like this:

{"Date":"10/21/2021 3:07:14 PM","CustomObject":[{"Data1":0,"Data2":"looool0","Data3":"target0"},{"Data1":1,"Data2":"looool1","Data3":"target1"},{"Data1":2,"Data2":"looool2","Data3":"target2"...<..>}]}

 

If you just need to wrap a List<> use this:

Code (CSharp):

1.  
2. [System.Serializable]
3. public class JsonableListWrapper<T>
4. {
5.     public List<T> list;
6.     public JsonableListWrapper(List<T> list) => this.list = list;
7. }
8.  

Then, using OPs problem as an example, they could just do this:

Code (CSharp):

1.  
2. List<string> stringList = new List<string>(){"one","two","three"};
3. // To Json
4. string stringListAsJson = JsonUtility.ToJson(new JsonListWrapper<string>(stringList));
5. // From Json
6. List<string> stringListFromJson = JsonUtility.FromJson<JsonListWrapper<string>>(stringListAsJson).list;
7.  

This is what I use to save/load user configured input to/from PlayerPrefs.

 

That just worked, thanks.
Now, why do we need to wrap it?

 

Because unity can't be bothered to fix their crappy JSON utility. Across the board, unity's ability to handle any type of stored/structured data is just garbage, and probably always will be.

 

Would this wrapper method work in a case where I have player info in a class but the class itself contains a List of more specific level info e.g.

Code (CSharp):

1. public class IG_CloudData
2. {
3.     public int version;
4.     public string name;
5.     public bool adsFree;
6.     public List<PlayerLevelInfo> levels;
7.     public int score;
8.     public string currentLevel;
9.     public string maxLevelUnlocked;
10. }
11.  
12. public class PlayerLevelInfo
13. {
14.     private string _level;
15.     private bool _status;
16.     private string _bestTime;
17.     private int _bestScore;
18.     private int _stars;
19.     private int _bestScore;
20. }

Here I'd like to serailise and deserialise IG_CloudData.

Thanks in advance,
LS

 

You already have the code typed in, make more code to test it.

Be sure to let us know what you find.

 

Newtonsoft JSON package maybe available for your version of Unity.

Quick research shows packages available 2019.1 - 2021.2 or check package manager. 2022 and up maybe natively installed.

Additional links
https://github.com/applejag/Newtonsoft.Json-for-Unity/wiki/Install-official-via-UPM
https://docs.unity3d.com/Packages/com.unity.nuget.newtonsoft-json@3.0/manual/index.html

 

Alternatively Unity provides a more advanced serialization package with custom JSON and binary formatters.

https://docs.unity3d.com/Packages/com.unity.serialization@3.1/manual/index.html

 

Alternatively alternatively there are other serialisers out there like the Odin Serializer: https://github.com/TeamSirenix/odin-serializer

 

I do not recommend Odin Serializer anymore. Unfortunately it seems it doesn't work with .Net Standard, only with .Net Framework. Which is limiting its use inside Unity.

 

I've only really used it as part of the overarching Odin Inspector package, where it comes as pre-compiled dlls, so I wasn't aware of these issues.