So, I have a list of Upgrade systems for my game but it has a bug on it when I press upgrade for a second time the index out of range then pressed for the third times the index out of range gone. this whole script.
void Start() { newSelectedIndex = previousSelectedIndex = PlayerPrefs.GetInt("currentPlayer"); btn = Select_Player[newSelectedIndex].GetComponent<Button>(); btn.interactable = false; Coins = M_CoinManager.instance.Coins; for (int i = 0; i < Select_Player.Length; i++) { priceText[i].text = Cost_Player[i].ToString(); value_player[i] = "" + i; Select_Player[i].SetActive(false); buyPlayer[i] = PlayerPrefs.GetInt(value_player[i]); } //if(PlayerPrefs.HasKey("currentPlayer")){ selectedVehicleIndex = PlayerPrefs.GetInt("currentPlayer"); theVehicles[selectedVehicleIndex].SetActive(true); VehicleInfo(); UpgradeButtonStatus(); } // Update is called once per frame void Update() { for (int i = 0; i < Select_Player.Length; i++) { buyPlayer[i] = PlayerPrefs.GetInt(value_player[i]); if (i == buyPlayer[i]) { Select_Player[i].SetActive(true); upgradeBtn[i].interactable = true; UpgradeButtonStatus(); } else { upgradeBtn[i].interactable = false; } } } public void BuyCharact(int id) { M_SoundManager.instance.playUIsfx(); if (Cost_Player[id] <= Coins) { M_CoinManager.instance.AddCoins(-Cost_Player[id]); PlayerPrefs.SetInt(value_player[id], id); } else { _CoinShake.DoShake(); Debug.Log("Does have enough coin"); } } public void Reset() { for (int i = 0; i < Select_Player.Length; i++) { PlayerPrefs.SetInt(value_player[i], 0); } } public void Select(int id) { previousSelectedIndex = newSelectedIndex; newSelectedIndex = id; newSelectedIndex = selectedVehicleIndex; PlayerPrefs.SetInt("currentPlayer", newSelectedIndex); Button newbtn = Select_Player[previousSelectedIndex].GetComponent<Button>(); btn = Select_Player[newSelectedIndex].GetComponent<Button>(); btn.interactable = false; newbtn.interactable = true; M_SoundManager.instance.playUIsfx(); Debug.Log("Selected TypeCar" + newSelectedIndex); } public void nextVehicle() { M_SoundManager.instance.playUIsfx(); theVehicles[selectedVehicleIndex].SetActive(false); selectedVehicleIndex = (selectedVehicleIndex + 1) % theVehicles.Length; theVehicles[selectedVehicleIndex].SetActive(true); VehicleInfo(); UpgradeButtonStatus(); } public void PreviousVehicle() { M_SoundManager.instance.playUIsfx(); theVehicles[selectedVehicleIndex].SetActive(false); selectedVehicleIndex--; if (selectedVehicleIndex < 0) { selectedVehicleIndex += theVehicles.Length; } theVehicles[selectedVehicleIndex].SetActive(true); VehicleInfo(); UpgradeButtonStatus(); } public void VehicleInfo() { currLevel = _VehicleStats[0].carItem[selectedVehicleIndex].unlockedLevel; levelText[selectedVehicleIndex].text = "Level: " + (currLevel + 1); powerText[selectedVehicleIndex].text = "Power: " + _VehicleStats[0].carItem[selectedVehicleIndex].vehicleLevel[currLevel].motorPower; brakeText[selectedVehicleIndex].text = "Brake: " + _VehicleStats[0].carItem[selectedVehicleIndex].vehicleLevel[currLevel].brakePower; Debug.Log(selectedVehicleIndex); } public void upgradeMethod() { nextLevelIndex = _VehicleStats[0].carItem[selectedVehicleIndex].unlockedLevel + 1; if (Coins >= _VehicleStats[0].carItem[selectedVehicleIndex].vehicleLevel[nextLevelIndex].unlockCost) { Coins -= _VehicleStats[0].carItem[selectedVehicleIndex].vehicleLevel[nextLevelIndex].unlockCost; _VehicleStats[0].carItem[selectedVehicleIndex].unlockedLevel++; if (_VehicleStats[0].carItem[selectedVehicleIndex].unlockedLevel < _VehicleStats[0].carItem[selectedVehicleIndex].vehicleLevel.Length - 1) { upgradeBtnText[selectedVehicleIndex].text = "Upgrade Cost :" + _VehicleStats[0].carItem[selectedVehicleIndex].vehicleLevel[nextLevelIndex + 1].unlockCost; } else { upgradeBtn[selectedVehicleIndex].interactable = false; upgradeBtnText[selectedVehicleIndex].text = "Max Level"; } VehicleInfo(); } } private void UpgradeButtonStatus() { if (_VehicleStats[0].carItem[selectedVehicleIndex].unlockedLevel < _VehicleStats[0].carItem[selectedVehicleIndex].vehicleLevel.Length - 1) { upgradeBtn[selectedVehicleIndex].interactable = true; nextLevelIndex = _VehicleStats[0].carItem[selectedVehicleIndex].unlockedLevel + 1; upgradeBtnText[selectedVehicleIndex].text = "Upgrade Cost :" + _VehicleStats[0].carItem[selectedVehicleIndex].vehicleLevel[nextLevelIndex + 1].unlockCost; } else { upgradeBtn[selectedVehicleIndex].interactable = false; upgradeBtnText[selectedVehicleIndex].text = "Max Level"; } } and the error reference to this line :
private void UpgradeButtonStatus() { if (_VehicleStats[0].carItem[selectedVehicleIndex].unlockedLevel < _VehicleStats[0].carItem[selectedVehicleIndex].vehicleLevel.Length - 1) { upgradeBtn[selectedVehicleIndex].interactable = true; nextLevelIndex = _VehicleStats[0].carItem[selectedVehicleIndex].unlockedLevel + 1; upgradeBtnText[selectedVehicleIndex].text = "Upgrade Cost :" + _VehicleStats[0].carItem[selectedVehicleIndex].vehicleLevel[nextLevelIndex + 1].unlockCost; } else { upgradeBtn[selectedVehicleIndex].interactable = false; upgradeBtnText[selectedVehicleIndex].text = "Max Level"; } } 
as you can see on the update that’s what I mean. after I press upgrade for the third times the error stopped.
and this from the inspector 
