How do I remove the last item from a list using indexes?

Questions & Answers
1

Hello,

I am creating a gallery where you can add and remove elements. I am using three buttons, one to add the elements (button), another to see the elements (button) and the last one is to remove the button from that element (button).

When I add a number of buttons and then delete a randomly selected one, it is deleted (the button and the reference in the list are destroyed) but if I try to eliminate the last button, it throws an index error out of range

This is my code:

using System.Collections.Generic;
using TMPro;
using UnityEngine;
using UnityEngine.UI;

public class CreateList : MonoBehaviour
{
    public GameObject _buttonPrefab;
   
    [HideInInspector]
    public Button _delete;

    public RectTransform _contentGallery;

    public List<GameObject> _buttonFileList = new List<GameObject>();

    public int _index;

    public int _currentGallery;

    private void Start()
    {
        _index = 0;
    }
    
    public void AddButtonList()
    {
        int tempIndex = _index;

        GameObject _spamButton = (GameObject)Instantiate(_buttonPrefab);
        Button _btnPlay = _spamButton.GetComponent<Button>();
        _spamButton.name = "Button" + "_" + (_index);

        _btnPlay.onClick.AddListener(() => ClikButtonList(tempIndex));

        TextMeshProUGUI var = _spamButton.GetComponentInChildren<TextMeshProUGUI>();
        var.text = "Button_" + _index.ToString();

        _delete = GameObject.Find("ButtonPrefabDelete").GetComponent<Button>();

        _delete.name = "Delete" + "_" + (_index);

        _delete.onClick.AddListener(() => DeleteButtonList(tempIndex));
        Debug.Log("tempIndex vale: " + _index);

        _spamButton.transform.SetParent(_contentGallery, false);
        _spamButton.transform.localScale = new Vector3(1, 1, 1);

        _buttonFileList.Add(_spamButton);

        _index += 1;
    }

    public void ClikButtonList(int index)
    {
        Debug.Log(index);
    }

    public void DeleteButtonList(int index)
    {
        Debug.Log(index);
        Destroy(_buttonFileList[index]);
        _buttonFileList.RemoveAt(index);

    }
}

I am doing something wrong?

Edit1: I add the package of my project, I am using unity 2019
Link: Gallery package

Edit2: If I add four elements in the list they would be from 0 to 3, if I eliminate the element 1 it is eliminated and the list is traversed, but if I eliminate the last value of the new list, element 2 gives me an error of value out of list range.

Image example

2

Problem is that you continuously increasing index and assigning it to buttons. When some buttons removed the remaining keeps incorrect indexes and it causes “out of range” error.
Example: you add 3 buttons (correct indexes:0,1,2) and remove first (incorrect remains indexes:1,2). Then you trying remove button with index 2 from array which contains only 2 elements (correct indexes:0,1) and you “get out of range” error.
There’s alot of way to go around it.
One example (use button GameObject instead of index):

    public void AddButtonList()
    {
        int tempIndex = _index;

        GameObject _spamButton = Instantiate(_buttonPrefab, _contentGallery, false);
        _spamButton.name = "Button" + "_" + (_index);

        Button _btnPlay = _spamButton.GetComponent<Button>();
        _btnPlay.onClick.AddListener(() => ClikButtonList(_spamButton));

        TextMeshProUGUI var = _spamButton.GetComponentInChildren<TextMeshProUGUI>();
        var.text = "Button_" + _index.ToString();

        _delete = GameObject.Find("ButtonPrefabDelete").GetComponent<Button>();
        _delete.name = "Delete" + "_" + (_index);
        _delete.onClick.AddListener(() => DeleteButtonList(_spamButton));

        _buttonFileList.Add(_spamButton);

        _index += 1;
    }

    public void ClikButtonList(GameObject button)
    {
        Debug.Log(button.name + " index:" + button.transform.GetSiblingIndex());
    }

    public void DeleteButtonList(GameObject button)
    {
        _buttonFileList.Remove(button);
        Destroy(button);
    }