Script on button does not work - NullReferenceException

Questions & Answers
1

Hi. I know there are many questions on NullReferenceException, but each have different code. I would like to know what I am missing in mine. This is testing code my project. The first script (MoneyScript) goes onto a text object-

78730-capture.jpg

using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class MoneyScript : MonoBehaviour {

	public int Money;
	Text MoneyText;
	BuildingUpgrade buildingUpgrade;

	// Use this for initialization
	void Awake () {
		MoneyText = GetComponent <Text> ();
		Money = 1000;
	}

	// Update is called once per frame
	void Update () {
		MoneyText.text = "$ " + Money;
	}

	public void doUpgrade(){

		if (Money >= buildingUpgrade.UpgradeCost) {

			Money -= buildingUpgrade.UpgradeCost;
		} else {

			Debug.Log("You do not have enough money to do the upgrade");
		}
	}


}

And this is the script for the value that the upgrade has -

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class BuildingUpgrade : MonoBehaviour {

	public int UpgradeCost = 500;
}

The text object is dragged onto the button onClick() and I access the method inside it doUpgrade()

78731-capture-2.jpg

But I get this error : NullReferenceException: Object reference not set to an instance of an object
MoneyScript.doUpgrade () (at Assets/Scrpits/MoneyScript.cs:24)

Why does the error come up and why can’t I subtract that amount from money?

2

You need to assign buildingUpgrade first. It is not assigned anywhere. You can do that by i.e.

void Awake () {
        buildingUpgrade = GameObject.Find("ObjectThatHasAddedBuildingUpgradeAsComponent").GetComponent<BuildingUpgrade>();