Unity: Cannot modify / add values to an array in System.Serializable

Question

I have a System.Serializable class

[System.Serializable]
public class _answersData
{
    public string word;
    public string wordmeaning;
    public string wordmeaning2;
    public GameObject result;    
}

I then have a monobehaviour class where an array of _answerData class is declared

public class gamePlay : MonoBehaviour
{
    public _answersData[] answersData;
}

I am then trying to add data to _answerData array from another script using below method

public class challengeScript: MonoBehaviour
{
    void Start()
    {
        gameplayScript = gameObject.GetComponent<gamePlay>();
        populate();
    }
    
    void populate()
    {
        answersCount = int.Parse(snapshot.Child("Answers").Child("Count").Value.ToString());
        gameplayScript.answersData = new _answersData[answersCount];

        for (int i = 0; i < answersCount; i++)
        {
            string positionNode = "Answer" + (i + 1).ToString();
            string _word = snapshot.Child("Answers").Child(positionNode).Child("Word").Value.ToString();
            gameplayScript.answersData[i].word = _word;   
        }
    }
}

but I am getting NullReferenceException at 'gameplayScript.answersData[i].word = _word' line

Here's the error:

NullReferenceException: Object reference not set to an instance of an object

Can someone guide what I am doing wrong here?

derHugo · Accepted Answer · 2021-09-01 08:41:17Z

1

Just because it is [Serializable] doesn't mean the elements are automatically created once you create the array. By default all reference type elements will still be null.

Only within Unity the Inspector itself automatically creates instances of [Serializable] types and initializes the array itself.

In code you have to actually create your element instances yourself like e.g.

var answerData = new _answerData();
answerData.word = _word;
gameplayScript.answersData[i] = answerData;

answered Sep 1, 2021 at 8:41

derHugo

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