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I need to declare an Array of Lists variable in Unity. Array size is fixed and it is 5. My code is working as i want, but i think there must be a better and a shorter way to do it:

public List<GameObject>[] charactersOnBoardSortedP1 = new List<GameObject>[] {new List<GameObject>(), new List<GameObject>(), new List<GameObject>(), new List<GameObject>(), new List<GameObject>() };

I tried to do like this:

public List<GameObject>[] charactersOnBoardSortedP1 = new List<GameObject>[5];

But i have an error: Object reference not set to an instance of an object.

Is there any way to declare my variable simpler? I mean if my array has only 5 slots it's ok, but what if 100? It's kind of stupid to copy new List... 100 times in declaration.

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  • 1
    You could use target-type. c# 9? feature eg. sharplab.io/… - learn.microsoft.com/en-us/dotnet/csharp/language-reference/… Commented Nov 6, 2021 at 17:11
  • Well an array of anything. You declare the array and make one of thr right size. Then if it has class based objects you would need to fill the array with the newly made class objects. Loops are often the easiest way to set it up Commented Nov 6, 2021 at 17:19
  • @Jim Hopper - You can accept the answer which is suitable for your solution Commented Nov 7, 2021 at 12:32
  • Why not use a loop? Commented Nov 7, 2021 at 15:44
  • Basically this is a duplicate of What is a NullReferenceException and how do I fix it since you create an array but didn't initialize the list instances Commented Nov 8, 2021 at 5:55

3 Answers 3

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2

try this. Test here

Create an Array of list variables. initialise each Array items to a new list of GameObject. then you can add to said array's list.

using System;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
                    
public class Program
{
    public static void Main()
    {
        // create array of lists
        List<GameObject>[] COBSP1 = new List<GameObject>[5]; //charactersOnBoardSortedP1
        // setup lists
        COBSP1[0] = new List<GameObject>();
        COBSP1[1] = new List<GameObject>();
        COBSP1[2] = new List<GameObject>();
        COBSP1[3] = new List<GameObject>();
        COBSP1[4] = new List<GameObject>();
        
        // add objects to said list
        COBSP1[0].Add(new GameObject());
        COBSP1[0].Add(new GameObject());
        COBSP1[0].Add(new GameObject());
        COBSP1[0].Add(new GameObject());
        
        COBSP1[1].Add(new GameObject());
        COBSP1[1].Add(new GameObject());
        COBSP1[1].Add(new GameObject());
        COBSP1[1].Add(new GameObject());
        
        COBSP1[2].Add(new GameObject());
        COBSP1[2].Add(new GameObject());
        COBSP1[2].Add(new GameObject());
        COBSP1[2].Add(new GameObject());
        
        COBSP1[3].Add(new GameObject());
        COBSP1[3].Add(new GameObject());
        COBSP1[3].Add(new GameObject());
        COBSP1[3].Add(new GameObject());
        
        COBSP1[4].Add(new GameObject());
        COBSP1[4].Add(new GameObject());
        COBSP1[4].Add(new GameObject());
        COBSP1[4].Add(new GameObject());
    }
    
}
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3 Comments

this could use a for loop if your COBSP1 array has a large amount of values.
Have in mind that new GameObject spawns a new object into the scene which might not really be what OP wants to do! I think OP only wants the list instances created but without any elements within them ;)
@derHugo COBSP1[4].Add(new GameObject()); is example code, re-correctly
2

try this

var  arraySize=6; //or what size you need

List<GameObject>[] charactersOnBoardSortedP1 = new List<GameObject>[arraySize];

charactersOnBoardSortedP1=  charactersOnBoardSortedP1
                           .Select(obsp => obsp = new List<GameObject>()) 
                            .ToArray();

or if you need to init some more things in the same time

for (var i=0; i<  charactersOnBoardSortedP1.Length; i++)
{
    charactersOnBoardSortedP1[i]=new List<GameObject>();
    // if you need to add some elements in the same time
    charactersOnBoardSortedP1[i].Add(new GameObject {Id=i});
}
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3 Comments

Have in mind that new GameObject spawns a new object into the scene which might not really be what OP wants to do! I think OP only wants the list instances created but without any elements within them ;)
@derHugo Thanks, As you can see I have 2 variants - one with empty list, another variant just shows the most comfortable (IMHO) way to add some objects to the list if needed.
Just wanted to mention that because seemingly not everyone knows how GameObject works ;) In the first code snippet the new List<GameObject>[arraySize]; is completely redundant though since later you anyway overwrite it via Linq
2

Easiest way to achieve it is as follows:

int arraySize = 5;
List<GameObject>[] charactersOnBoardSortedP1 = Enumerable.Repeat(new List<GameObject>(), arraySize).ToArray();

This will create array of specified size filled with empty List<GameObject>()

If you wish to have list to have GameObject you can modify above code a bit.

int arraySize = 5;
List<GameObject>[] charactersOnBoardSortedP1 = Enumerable.Repeat(new List<GameObject> { new GameObject()}, arraySize).ToArray();
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2 Comments

Have in mind that new GameObject spawns a new object into the scene which might not really be what OP wants to do! I think OP only wants the list instances created but without any elements within them ;)
@derHugo I have mentioned solution for that as well.

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