Unexpected increase in List.Count after adding elements to the list

Question

After running the following loop (one iteration), battleshipParts.Count returns 2.

The code is ran once in the ScriptableObject.Awake

for (byte i = 0; i < 1; i++)
{
    var battleshipPart = CreateInstance<BattleshipPart>();
    battleshipPart.battleshipData = this;
    battleshipParts.Add(battleshipPart);
}

I tried using the debugger and walking through the code, after the execution of

battleshipPart.battleshipData = this;

battleshipParts.Count is already 1

battleshipPart.battleshipData is used to hold a reference to its battleship parent. Implementation:

public class BattleshipPart : ScriptableObject
{
    public Vector2 gridPosition;
    public BattleshipData battleshipData;
    public bool isHit = false;
}

The battleshipParts list isn't modified anywhere else besides this code. Besides. Why would it update itself with a null value after running battleshipPart.battleshipData = this;?

Where is `battleshipParts` declared and initialized? Where else is it used in any code anywhere? — Retired Ninja, Jun 07 '23 at 21:41
At the top of the caller class (`this` in the code provided) `public List battleshipParts = new List();` — Phillip Zoghbi, Jun 07 '23 at 21:57
Consider putting together a [mcve] so we can see the full picture. — Retired Ninja, Jun 07 '23 at 22:13
as the list is not cleared before the loop if that code runs twice you would have 2, or 3 or more depending on how many times it ran — BugFinder, Jun 07 '23 at 22:27
@BugFinder Clearing the list worked, but not for the reason I would've thought. Surprisingly enough, `ScriptableObject.Awake` was invoked from assigning the reference to this object in the inspector. According to [Unity's docs](https://docs.unity3d.com/ScriptReference/ScriptableObject.Awake.html) that should've only happened when the game runs. — Phillip Zoghbi, Jun 07 '23 at 23:16
A scriptable object retains its state variables until explicitly set. It is easy to see this by adding a bool, press play and set it true, then hit stop in the editor. The bool will stay true. This is a bit different than monobehaviours, which may be the cause of confusion. — hijinxbassist, Jun 08 '23 at 00:06
You're right, values stay remembered in the `.asset` files. However, I'm cloning the instance, and `Awake` shouldn't have been called by the inspector. At least not according to the docs. — Phillip Zoghbi, Jun 08 '23 at 03:25

score 0 · Answer 1 · answered Jun 09 '23 at 16:33

This error because you create Instance not Asset and trying to save it into list.

Just create .asset(ScriptableObject) file with AssetDatabase in project.

    for (byte i = 0; i < 1; i++)
    {
        BattleshipPart battleshipPart = ScriptableObject.CreateInstance<BattleshipPart>();
        AssetDatabase.CreateAsset(battleshipPart, $"Assets/BattleshipPart_{i}.asset");
        AssetDatabase.SaveAssets();

        battleshipPart.battleshipData = this;
        battleshipParts.Add(battleshipPart);
    }

If you don't want to create asset file in your project, just use simple serialized class not ScriptableObject.

Unexpected increase in List.Count after adding elements to the list

1 Answers1