Unknown reason for "ArgumentOutOfRangeException: Argument is out of range. Parameter name: index" exception - list

Question

I am making a Unity game where the player is collecting data about aliens.
Therefor the player points on the alien and uses something like a camera.
Camera --> shoots Ray --> Ray returns all needed data attached to the script on the alien-gameobject
void ShootRay()
{
RaycastHit hitInfo; // stores information about hitted object
if (Physics.Raycast (transform.position, transform.forward, out hitInfo, maxRaycastRange, 1 << LayerMask.NameToLayer("creature"))) // out hitInfo = Unity puts information in the variable hitInfo
{
// UI alerts and collecting dna
if (hitInfo.distance <= photoRaycastRange)
{
distanceInfo.text = "scanning_genome";
if (hitInfo.collider.gameObject.GetComponent<EnemyAI> ().dna_collected == false) {
if (dna_percent_0_to_1 < 1)
{
calming_dna_scan_circle = false;
distanceInfo.text = "scanning_genome";
dna_percent_0_to_1 += Time.deltaTime * dna_scanSpeed;
dna_collect_circle.fillAmount = dna_percent_0_to_1;
}
else if (dna_percent_0_to_1 >= 1)
{
// adding info of creature to database
if (hitInfo.collider.gameObject.GetComponent<EnemyAI> ().raceIndex == 1)
{
if (!raceOneWasAdded)
{
BestiariumData.scannedSpecies.Add (hitInfo.collider.gameObject);
raceOneWasAdded = true;
}
BestiariumData.dnaBar_1 += 0.25f;
The mentioned database is simply a class called BestiariumData with:
public static List<GameObject> scannedSpecies = new List<GameObject> ();
public static List<float> savedDNAFillRates = new List<float> ();
public static float dnaBar_1 = 0;
public static float dnaBar_2 = 0;
public static float dnaBar_3 = 0;
public static float dnaBar_4 = 0;
public static float dnaBar_5 = 0;
public static float dnaBar_6 = 0;
public static float dnaBar_7 = 0;
public static float dnaBar_8 = 0;
}
I'm having a menu where the player can check which aliens he/she already has collected data. The name of the alien is displayed (Monster One, ...) and a progress bar for how many alien individuals the player has scanned.
THE PROBLEM:
if I try to assign the NAME of the status bar if throws the ArgumentOutOfRangeException: Argument is out of range. Parameter name: index exception. I am doing this by setting a bool in another script to true.
public List<GameObject> monsterButtons = new List<GameObject>();
public static bool nameButtons = false;
// Update is called once per frame
void LateUpdate ()
{
if (nameButtons)
{
for (int buttonIndex = monsterButtons.Count; buttonIndex > 0; buttonIndex--)
{
monsterButtons [buttonIndex].GetComponentInChildren<Text> ().text = BestiariumData.scannedSpecies [buttonIndex].name;
}
}
}
Thank you for your help.

Answer 1

Button index gives the count of your list. So say your list contains 10 items, count will be 10.
However a list's index starts at 0, not 1.
So when you try to access monsterButtons [buttonIndex] for the first time, you are calling index 10, which means item 11. This does not exist so throws your error.
To fix, add "-1" to your index asigning:
for (int buttonIndex = monsterButtons.Count -1; buttonIndex >= 0; buttonIndex--)
{
monsterButtons [buttonIndex].GetComponentInChildren<Text> ().text = BestiariumData.scannedSpecies [buttonIndex].name;
}