//SOLVED Can't add to a class's list from inside a for loop

Unity Engine
1

So I’m a bit perplexed here. Basically, I’m trying to add a position to a List in another class. That class looks like this:

public class TileItems
{
    public string InstanceID;
    public List<ChildObject> ChildObjects;
    public List<Vector3> ChildObjectPositions;
}

And the for loop is pretty simple:

public TileItems tiles;
public void SaveChildTransformData()
    {
        //for each child object
        for (int i = 0; i < transform.childCount; ++i)
        {
            tiles.ChildObjectPositions.Add(transform.GetChild(i).position);
            print("Found child: " + transform.GetChild(i).name);
            foreach (Component comp in transform.GetComponents<Component>())
            {
                childClass.ChildComponents.Add(comp);
            }
            tiles.ChildObjects.Add(childClass);
            //tiles.ChildObjectPositions.Add(transform.GetChild(i).position);
            Debug.Log("Saved child info at position " + transform.GetChild(i).position);
        }
    }

However, the “tiles.ChildObjectPositions.Add etc…” line doesn’t work inside the for loop, but as soon as I put it above the for loop, it works. Also, my for loop is working as the Debug.Logs show in the console.

Why can’t I add to another class’s list in a for loop, and how can I get around this?

If I didn’t explain something, let me know. Thank you for any help!

2

I managed to get this working by just adding

     public List<Vector3> ChildObjectPositions = new List<Vector3>();

when you declare the list, i think it needs to be initialized (i do this with every collection item e.g. dictionary/list)

Code Below:

    [System.Serializable]
    public class TileItems
    {
        public string InstanceID;
       // public List<ChildObject> ChildObjects;
        public List<Vector3> ChildObjectPositions = new List<Vector3>();
     
    }
    public TileItems tiles;

    void Start()
    {
        SaveChildTransformData();
    }
    public void SaveChildTransformData()
    {
        //for each child object
        for (int i = 0; i < transform.childCount; ++i)
        {
            tiles.ChildObjectPositions.Add(transform.GetChild(i).position);
            print("Found child: " + transform.GetChild(i).name);
            foreach (Component comp in transform.GetComponents<Component>())
            {
               // childClass.ChildComponents.Add(comp);
            }
          //  tiles.ChildObjects.Add(childClass);
            //tiles.ChildObjectPositions.Add(transform.GetChild(i).position);
            Debug.Log("Saved child info at position " + transform.GetChild(i).position);
        }
    }

Result:https://gyazo.com/efc3328af89f73e9277ae56e8d75e773

3

When you say it “doesn’t work”, is it giving you an error? Or are you just getting different positions in there than you expected?

There’s nothing in C# that forbids you from adding to another class’s list from a for loop; so it’s much more likely you just made a mistake somewhere. You shouldn’t modify a list while looping through that list, but it doesn’t look like that’s what you’re doing, so it wouldn’t apply in this case.

4

It just doesn’t add anything at all, the list stays empty. No errors.

And Rob’s answer didn’t work for me. Fun times for me…

5

Are you calling the function anywhere? where is SaveChildTransformData(); being called?

6

It is being called as my Debug.Logs are firing. I made this:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[System.Serializable]
public class TestClass1
{
    public List<Vector3> Testing;
}

public class TestList : MonoBehaviour {
    public TestClass1 test;
    // Use this for initialization
    void Start ()
    {
        for (int i = 0; i < 5; i++)
        {
            test.Testing.Add(new Vector3(i, 2, 3));
            Debug.Log("Ran");
        }
    }
}

And even without the “new List…” it works great. So it’s something else in my code; it’s gotten pretty complex.

7

so your TestClass is working fine? then it might be something wrong with the Foreach loop?

8

This is the strangest thing I’ve seen in coding. I made a completely different TileItems class (renamed it) and it also doesn’t work, even though the same thing works in another script that I posted above. At this point I’ve commented out everything in the for loop except adding to the class.

Also, I know it’s not being cleared in any way as adding data in the Editor before playing keeps what I wrote in the Inspector; just nothing can be added in the loop.

9

FINALLY! Found what was wrong. Turns out that because the tile is procedurally generated, I was running that code BEFORE there were any children spawned, so transform.childCount was 0. ANOTHER tile had spawned children, and IT was spamming the console, but I was looking at the Inspector of the tile that ran the code before any children were spawned. Also, I learned that Awake is run regardless if a script is enabled or disabled, so that caused issues for me too.

So I was looking in the wrong place all along. Anyways, thanks for trying to help; sorry for wasting your time on something that wasn’t an issue.

1 Like