JSON - Unity: How can I serialize a list? NullReferenceException error

Question

Here is the code I've been trying to use to serialize a list into JSON:

void Save()
        {
            Debug.Log("Save");

            InfoSaveList saveList = new InfoSaveList();

            // this steps through information nodes and collects 
            // the information they contain
            foreach (BaseNode n in rootNode.childrenNodes)
            {
                var id = n.nodeID;
                var info = n.infoLine;

                InfoSave infoSaveData = new InfoSave();
                infoSaveData.nodeID = id;
                infoSaveData.info = info;

                saveList.infoSave.Add(infoSaveData);

            }
            string infoSaveDataToJson = JsonUtility.ToJson(saveList, true);
            Debug.Log(infoSaveDataToJson);
        }


[System.Serializable]
public class InfoSave
{
    public int nodeID;
    public string info;

}

[System.Serializable]
public class InfoSaveList
{

    [SerializeField] public List<InfoSave> infoSave;
}

for some reason I'm getting the error:

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

on the line:

saveList.infoSave.Add(infoSaveData);

I can't figure out why that would be the case, I'm trying to step through my code and it all seems to make sense to me but I'm clearly missing something.

If i get through this error, will this even save correctly as JSON? or can that only be done with arrays no lists?

Hellium · Accepted Answer · 2019-01-31 12:52:22Z

2

You simply never instantiate your list.

Either do it through a constructor, when declaring the list, or from your Save function since the list is public.

// Constructor :

[System.Serializable]
public class InfoSaveList
{

    [SerializeField] public List<InfoSave> infoSave;

    public InfoSaveList()
    {
         infoSave = new List<InfoSave>();
    }
}

// Declaration :

[System.Serializable]
public class InfoSaveList
{

    [SerializeField] public List<InfoSave> infoSave = new List<InfoSave>();
}

// From Save function

void Save()
{
    // ...
    InfoSaveList saveList = new InfoSaveList();
    saveList.infoSave = new List<InfoSave>();
    // ...
}

answered Jan 31, 2019 at 12:52

Hellium

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1 Comment

Kabir Over a year ago

I'm so dumb, this was it! Thanks!

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