JSON Error : ArgumentException: JSON must represent an object type.

Question

I am using the following script:

 [System.Serializable]
 public class Choice
 {
     public string choice;
     public int votes;
 }
 
 [System.Serializable]
 public class RootObject
 {
     public string question;
     public string published_at;
     public List<Choice> choices;
 }

For the following JSON data:

[

{ "question": "Favourite programming language?", "published_at": "2015-08-05T08:40:51.620Z", "choices": [ { "choice": "Swift", "votes": 2048 }, { "choice": "Python", "votes": 1024 }, { "choice": "Objective-C", "votes": 512 }, { "choice": "Ruby", "votes": 256 } ] } ] And I am getting this Error message in console : ArgumentException: JSON must represent an object type. Please tell me what I am doing wrong.

Answer 1

Best Answer

Answer by JDelekto · Apr 03, 2019 at 07:59 AM

At first glance, it looks like your JSON defines an array of RootObject objects, but you are trying to deserialize a single RootObject. If you are always getting an object with this JSON and only expect one object, you have two choices: a) remove the '[' and ']' array designator from the JSON string and deserialize as a RootObject or deserialize the JSON as a RootObject array (i.e. RootObject[]) and always take the first element of the array (if its length is not zero).

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Kaustav_Brainium · Apr 03, 2019 at 09:14 AM 0

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Thank You!

Bunny83 · Apr 03, 2019 at 10:09 AM 0

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Note that (up to this point) the Unity's JsonUtility does not support an array as root object. It always expects an object as root element. If you want / need an array and want to use Unity's JsonUtility, you have to wrap your array in an object.

For more questions about Unity's JsonUtility, have a look at this SO question. If you're just looking for a way to easily read arbitrary json, have a look at my SimplyJSON framework

JDelekto Bunny83 · Apr 03, 2019 at 10:43 AM 0

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Interesting, I did not know Unity originally lacked the support for the collections. Normally I would not do what I suggested first, which was removing the square brackets but would instead deserialize to a collection if the server was handing it off that way.

The SO link you provided was great in the context of Unity; however, it is good to know that they now support arrays in Unity's basic class.

I typically dislike wrapping the array as a property of some other object unless it was done with a generic so as to limit the number of classes in a project if I have several different serialized types.

JSON Error : ArgumentException: JSON must represent an object type.

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