Unity3D JSON Deserializing Empty List?

Question

I have a web service that returns an empty list (just []).

JsonUtility.FromJson is giving me an

ArgumentException: JSON must represent an object type.

I have isolated this down to a bit of code as simple as:

string empty = "[]";
FriendManager.FriendList test = JsonUtility.FromJson<FriendManager.FriendList>(empty);
Assert.IsNotNull(test);

FriendList is just a wrapper for Friend[]. I also tried List<Friend>:

string empty = "[]";
FriendManager.FriendList test = JsonUtility.FromJson<List<Friend>>(empty);
Assert.IsNotNull(test);

Am I missing something obvious?

I have control over the server data (Spring Boot JSON web service) and the client (Unity3D).

derHugo · Accepted Answer · 2018-12-11 18:29:53Z

1

You can't use JsonUtility with a type like List directly, you have to use it with a defined class or struct type

so your second attempt will not work. And you also cannot directly asign it to FriendManager.FriendList if it s of type List<Friend> as you said.

You rather need a wrapper class for it like e.g.

[Serializable]
public class FriendList
{
    public List<Friend> Friends = new List<Friend>();
}

make FriendManaget.FriendList of type FriendList

And than either the server or you have to append the field name to that array namely the name of the variable: Friends e.g. like

FriendManager.FriendList test = JsonUtility.FromJson<List<Friend>>("\"Friends\":" + empty);

or the server has to send

"Friends":[]

answered Dec 11, 2018 at 6:56

derHugo

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1 Comment

Yup, that was it - thanks! I wound up changing the server implementation - want it to be as friendly as possible for Unity3D.