Json utility - save and load a list

Unity Engine
,
1

As the title says.

If I have a class:

public class MyList
{
public List class;
}

How can I check if a json file exists, and if not create one? And then how can I load this list, and save it when I need to? I’ve read up on JSON Utility but can’t figure out how to get a list to save and load correctly.

Also, on topic, I know json utility works with Lists, but how does it handle serializing derived classes? For example, using the code above, if I had a public class SomeClass, and then a public class OtherClass : SomeClass and the list above contained both of these.

2

Use File.Exists(…) to check if a file already exists. If you wish to write a Json file, you’d do something like this:
var class = new MyList();
var outputString = JsonUtility.ToJson(class);
File.WriteAllText(“C:\MyFile.json”, outputString);

In reverse, you can deserialize anything doing this:
var inputString = File.ReadAllText(“C:\MyFile.json”);
var class = JsonUtility.FromJson<MyList>(inputString);

3

Oh, and on the topic of derived classes: you might as well just try it out for yourself, but if something’s public in a root type, it’s still public in the derived class and JsonUtility will be able to read/write from it.

4

Thank you very much for your reply. Very concise! I will try this when I get home.

On the topic of derived classes, what I meant was; normally to populate my list I would do:

Add (new SomeClass(constructor variables here));

Or:

Add (new OtherClass  (constructor variables here));

I know unity’s serializer struggles to deserialize derived classes, and they deserialize as the parent class type. Do you still have this problem using JSON UTILITY?

1 Like
5

I work with deserialization a lot, but I can’t say I have been working with the JsonUtility and deserialization of derived types that much. Maybe it’s a good idea to create a demo project which tests only that. I’d try it for you right now, but I’ve got some other bugfixing to do :slight_smile:

6

Okay so I got this working, however I was right about the derived class issue. Going to try and derive from ScriptableObject and see if this fixes the issue

7

Seems weird that you wouldn’t be able to. In the message you made before you edited it you should try to make a wrapping class containing the array, and (de)serializing that instead.

[System.Serializable]
public class WrappingClass {
    public List<Item> Inventory;
}
var variable  = new WrappingClass() { Inventory = someOtherList };
JsonUtility.ToJson(variable);

I’m not too sure about JsonUtility being able to directly convert a list or array to a generic Json array.

2 Likes
8

Hiya, hey I’ve been using this quite a bit for saving and loading through json, it’s really handy.
Just wondering, is there a way to make the list generic? It’s just that I’ve ended up with a bunch of different wrapping classes for different types and It would be nice to just have one generic one.

9

You are such a hero. Thank you so much!!