2D list of gameobjects - array, generic list, or whatever

I'd been trying all afternoon to figure out how to create and use some form of 2D array so I can organize four columns of gameobjects and refer to them by numeric indexes. I just can't seem to get there.

I tried a list of lists but I always get null pointer errors when trying to populate the lists

List<List<GameObject>> CardColumns = new List<List<GameObject>>();
List<GameObject> Column1 = new List<GameObject>();
List<GameObject> Column2 = new List<GameObject>();
List<GameObject> Column3 = new List<GameObject>();
List<GameObject> Column4 = new List<GameObject>();

in Start()

CardColumns.Add(Column1);
CardColumns.Add(Column2);
CardColumns.Add(Column3);
CardColumns.Add(Column4);

Later in a function
CardColumns[0].Add(newGO);

Which tosses an argument out of range error.

I've also tried it with an array of lists and messed with regular arrays but got nowhere. Obviously I'm missing something pretty basic. What is it?

 

Looks fine to me - you should make sure if you're instantiating something that you're not getting a null gameobject. Sometimes it's hard to ensure you actually got the game object - usually I stick with storing the transform instead in arrays.

What's your method for procuring the game object you're trying to store?

 

I'm instantiating a prefab UI Image. After instantiating I get its recttransform and change the anchorposition and when I check the object is good.

What I have figured out is that CardColumns.Add(ColumnX) doesn't do anything. CardColumns.Count reports 0 elements right after adding the four columns.

 

Never mind, I just figured it out. It looked like a scope problem because the lists worked in Start() but were null inside a function. While I was staring at the debug output it finally dawned on me that the function debugs were appearing before the ones in start... I'd been calling the functions from start BEFORE the list/array work.

Definitely a DOH!

 

Here is a plugin to create 2D generic list in unity.
https://www.assetstore.unity3d.com/en/#!/content/51650