Unity Increasing List's size at runtime

Question

This is driving me crazy. I'm trying to simply increase the size of a list via script.

I've tried to set the List size before I reference it by saying

List<int> listName = new List<int>(20);

but this does not work. Nothing happens. Not even in Awake or Start.

I've tried to increase the size by doing this in a loop:

foreach(var line in table)
{
    int tempInt = new int();
    intList.Add(tempInt);
}

this works and my list size increases.

But my problem is that AFTER increasing this list's size I cannot reference any of the elements created at runtime. I can't reference intList[2] for example.

I've tried doing this in a normal void and IEnumerator and neither work.

All I want to do here is increase my list's size as it is needed and then reference to those list items as needed....

As simple as this problem sounds this is honestly the most annoying coding issue I have ever faced in Unity.

PLEASE help.

EDIT: Here;s the code I'm using...

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

public class DataExtraction : MonoBehaviour
{
    [Header("Tables")]
    public List<DataItem> tables; // The main table that needs to be populated
    
    [Header("Extraction Variables")]
    public string webAddress = "https://old.winningform.co.za/ECP/2F200717_1.htm"; // URL that the data will be extracted from 
    //(note this URL will be deleted after 17 July 2020 
    
    public List<string> rawDataSplit; // Place to store each line of the raw data
    public int currentTable = 0;
    
    void Awake()
    {
        DataItem newDataItem = new DataItem();
        tables.Add(newDataItem);
    }
    
    void Start()
    {
        if(webAddress != "")
        {
            StartCoroutine(GetRequest(webAddress));
        }
    }
    
    IEnumerator GetRequest(string uri)
    {
        using (UnityWebRequest webRequest = UnityWebRequest.Get(uri))
        {
            yield return webRequest.SendWebRequest();

            string[] pages = uri.Split('/');
            int page = pages.Length - 1;

            if (webRequest.isNetworkError)
            {
                Debug.Log(pages[page] + ": Error: " + webRequest.error);
            }
            else
            {
                string rawData = webRequest.downloadHandler.text;
                
                // Splitting the data into lines and assigning it to rawDataSplit list
                var linesInText = rawData.Split('\n'); 
                
                foreach(var line in linesInText)
                {
                    if(line != "")
                    {
                        rawDataSplit.Add(line);
                    }
                }
                //
                
                // Data has been split and assigned to the rawDataSplit list
                AssignTableData();
                //
            }
        }
    }
    
    void AssignTableData()
    {
        foreach(var line in rawDataSplit)
        {
            // When the script finds this line it indicates that a new Table has been found in the text
            // This will create a new table in the list and increase the currentTable number by 1 (to be used as an index number)
            // The following lines of data after that will then be added to THAT table until the next table is found...
            // A new table will again be created and the information will be added there instead.
            if(line.Contains("<table border"))
            {
                currentTable++;
                
                DataItem newDataItem = new DataItem();
                tables.Add(newDataItem);
                
                tables[currentTable].rawTableData.Add(line);
            }
            else // If not found automatically add information into Table index 0 (created at Awake)
            {
                print(tables.Count.ToString());
                tables[currentTable].rawTableData.Add(line);
            }
        }
    }
}

[System.Serializable]
public class DataItem
{
    public List<string> rawTableData;
}

ERROR:

NullReferenceException: Object reference not set to an instance of an object
DataExtraction.AssignTableData () (at Assets/DataExtraction.cs:89)
DataExtraction+<GetRequest>d__6.MoveNext () (at Assets/DataExtraction.cs:63)
UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) (at C:/buildslave/unity/build/Runtime/Export/Coroutines.cs:17)

Answer 1

Lists should automatically increase in size. Arrays do not. You should not need to set a size of the List, but the idea is that it would help with performance.

The code you mentioned:

foreach(var line in table)
{
    int tempInt = new int();
    intList.Add(tempInt);
}

should effectively add 20 default int's to the list. So they should all be set to 0. Are you somehow overriding your values? How are you setting your actual values? Can you provide more details on how you're adding values to the list, and then how you're using them?

If you're setting values in the editor, in the inspector, then you should be careful not to re-initialize the list as this would wipe out anything coming from the editor. How are you storing this list? It's not clear if you're using a public or private field, or property or something that's being instantiated inside a method.

Answer 2

The constructor parameter is the initial capacity of the internal array used by the list. The initial item Count is always 0. You can only access indexes in the range [0 .. Count - 1] (including Count - 1). The initial capacity does not change this.

You can only change the apparent size given by Count by adding or removing items with Add, AddRange, Clear, Insert, InsertRange and one of the 4 Remove variants.

A good initial capacity contributes in minimizing the number of required internal array resize operations but has no visible effect otherwise.

Therefore, if you have an index which might exceed Count - 1, you should get items with

if (i < list.Count) {
    int item = list[i];
    Process(item);
}

---

If you need a fixed collection size, use an array instead:

const int N = 20;
int[] arrayName = new int[N];

Now you can access all the indexes in the range [0 .. N - 1] (including N - 1).

---

If all this does not work, then maybe the list you are trying to access is not the same you initialized. If it is a class field, then maybe the it is in another object of the same class type. If it is a local variable (a variable declared inside a method), then it will only live during a single call of this method. (I'm not talking about enumerators and async/await here.)

See: List Class (Microsoft Docs)

Answer 3

Your question actually has nothing to do with the list count or indices at all!

The actual issue: You never initialize the rawTableData list so it is null when trying to add elements to it in

tables[currentTable].rawTableData.Add(line);

You should simply declare it as

[System.Serializable]
public class DataItem
{
    public List<string> rawTableData = new List<string>();
}