Beginner Problem: NullReferenceException

Unity Engine
1

Hello! The error that I am currently getting is:
NullReferenceException: Object reference not set to an instance of an object
Block.CountBreakableBlocks () (at Assets/Scripts/Block.cs:23)
Block.Start () (at Assets/Scripts/Block.cs:16)

Here’s the code that I think is relevant to this question:
First, block.cs:

using UnityEngine;

public class Block : MonoBehaviour
{
    [SerializeField] private AudioClip breakSound;
    [SerializeField] private AudioClip clunkSound;

    //Cached reference
    private Level level;

    private GameSession gamestatus;
    [SerializeField] private GameObject particleEffect;

    private void Start()
    {
        CountBreakableBlocks();
        gamestatus = FindObjectOfType<GameSession>();
        level = FindObjectOfType<Level>();
    }

    private void CountBreakableBlocks()
    {
        level.CountBlocksRemaining();
    }

    private void OnCollisionEnter2D(Collision2D collision)
    {
        BreakIfBreakable();
    }

    private void TriggerParticleEffect()
    {
        GameObject particles = Instantiate(particleEffect, transform.position, transform.rotation);
        Destroy(particles, 2f);
    }

    private void BreakIfBreakable()
    {
        if (CompareTag("Breakable"))
        {
            AudioSource.PlayClipAtPoint(breakSound, Camera.main.transform.position); //Play audio SFX
            Destroy(gameObject);
            TriggerParticleEffect();
            level.BlockDestroyed();
            gamestatus.AddPoints();
        }
        else
        {
            AudioSource.PlayClipAtPoint(clunkSound, Camera.main.transform.position);
        }
    }

level.cs:

using System;
using UnityEngine;

public class Level : MonoBehaviour
{
    [SerializeField] int blocksRemaining = 0; //Serialized for debugging

    //Cached reference
    SceneLoader sceneLoader;
 
    private void Start()
    {
        sceneLoader = FindObjectOfType<SceneLoader>();
    }
     
    public void CountBlocksRemaining()
    {
        blocksRemaining++;
    }

}

Here’s some more information about the project if it’s relevant at all:
It’s a block breaker game, similar to Atari Breakout
I’m using the “Complete C# Unity Developer 2D: Learn to Code Making Games” course made by GameDev.tv

Thanks in advance for your help!

2

A null reference exception occurs when you try to use a variable that doesn’t have a value.

You are assigning a value to the “level” variable on line 18. But on line 16 you call a function that tries to use the variable, even though it doesn’t have a value yet.

1 Like
3 
private void Start()
    {
        CountBreakableBlocks();
        gamestatus = FindObjectOfType<GameSession>();
        level = FindObjectOfType<Level>();
    }

You’re calling CountBreakableBlocks first, which method is using the “level” variable which is filled two lines after this.
I’m not sure the level = FindObjectOfType(); but if it is correct, just move to before the CountBreakableBlocks(); call.

4

Oh! Thank you guys very much! I completely missed that.