object reference not set to an instance of an object (HELP)

Good day everyone,

I'm making a game where you literally run away from a few dudes who are trying to kill you and I would like to make a system in which when you are 10 units on the Z axis away from the enemy, you will take damage.

This is my PlayerHealth class:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class PlayerHealth : MonoBehaviour
6. {
7.     public float maxHealth;
8.     public float currentHealth;
9.    
10. }
11.  

This is my (I say my but I honestly mean Brackey's) EnemyController script:

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.AI;
3. using System.Collections;
4.  
5. /* Makes enemies follow and attack the player */
6.  
7.  
8. public class EnemyController : MonoBehaviour
9. {
10.  
11.     public float lookRadius = 10f;
12.  
13.     Transform target;
14.     NavMeshAgent agent;
15.     PlayerHealth playerHealth;
16.  
17.     void Start()
18.     {
19.         target = PlayerManager.instance.player.transform;
20.         agent = GetComponent<NavMeshAgent>();
21.     }
22.  
23.     void Update()
24.     {
25.         // Get the distance to the player
26.         float distance = Vector3.Distance(target.position, transform.position);
27.  
28.         if (distance <= lookRadius)
29.         {
30.             // Move towards the player
31.             agent.SetDestination(target.position);
32.             if (distance <= 10f)
33.             {
34.                 // Attack
35.                 playerHealth.currentHealth -= 1f;
36.                 FaceTarget();
37.             }
38.         }
39.     }
40.  
41.     // Point towards the player
42.     void FaceTarget()
43.     {
44.         Vector3 direction = (target.position - transform.position).normalized;
45.         Quaternion lookRotation = Quaternion.LookRotation(new Vector3(direction.x, 0, direction.z));
46.         transform.rotation = Quaternion.Slerp(transform.rotation, lookRotation, Time.deltaTime * 5f);
47.     }
48.  
49.     void OnDrawGizmosSelected()
50.     {
51.         Gizmos.color = Color.red;
52.         Gizmos.DrawWireSphere(transform.position, lookRadius);
53.     }
54.  
55. }

When I play the game and I am within range, I get the error 'NullReferenceException: Object reference not set to an instance of an object EnemyController.Update () (at Assets/Scripts/EnemyController.cs:35).

Could someone please help?

Much appreciated

 

A NullReferenceException tells you that you are accessing a something in a reference which is null, meaning it was not yet assigned, or does not exist anymore. In your case, the error tells you it's at EnemyController.cs:35, meaning line 35. In line 35 you wrote playerHealth.currentHealth -= 1;
The problem here is that you never assigned the playerHealth reference to anything (no PlayerHealth object exists there), thus you effectively write null.currentHealth -= 1, which throws the exception. To fix that you need to create the object you want to use. It may be enough to write playerHealth = new PlayerHealth() in the Start() method, but i assume you want it to reference the actual health of your player, which you probably already created somewhere else. In that case you should reference that specific PlayerHealth object.

On that note, if you do not use any of the Monobehaviour methods (Start, Update, ..) a class does not need to be derived from Monobehavior. So for PlayerHealth this is not necessary.

Hope this helps

 

Adding that to Start wouldn't work either as each enemy would then have a different PlayerHealth value. Plus, new doesn't work if the class does inherit from Monobehaviour

 

Hey thanks a lot for the reply, I appreciate it, you helped me figure out what I was doing wrong. The only problem is that I still don't know how to fix it
I tried the solutions you gave me but like @Brathnann said, it doesn't work.

I searched for a fix but I literally found nothing.

 

If you have a playerHealth component in the scene, either you need to drag and drop that object into the enemy playerHealth variable (if your enemies already exist) or you could just make it a singleton script since you'll only ever have one playerHealth. Otherwise, you'll want some sort of manager script that can assign that playerHealth instance to the enemies (if you are spawning in new enemies).

 

You need to access your playerhealth somehow, Can we see the Player and PlayerManager script?

My guess it that you'll be able to do this instead:

PlayerManager.instance.player.health.currentHealth -= 1f;

If all depends on whether your player script exposes the playerHealth component though.

 

To be fair I don't really have a playermanager script, it's just this

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class PlayerManager : MonoBehaviour
6. {
7.  
8.     #region Singleton
9.  
10.     public static PlayerManager instance;
11.  
12.     private void Awake()
13.     {
14.         instance = this;
15.     }
16.  
17.     #endregion
18.  
19.     public GameObject player;
20.  
21. }

 

Thank you! This worked

 

Hmmmm guys i am also using brackeys code but i have and error i am trying to make the player die after falling or hitting an obstacle but it shows me
NullReferenceException: Object reference not set to an instance of an object
PlayerCollision.OnCollisionEnter (UnityEngine.Collision collision
i have no idea what is wrong here is the code that has the error



using UnityEngine;
public class PlayerCollision : MonoBehaviour
{

public PlayerMovement movement;

void OnCollisionEnter (Collision collision)
{
if (collision.gameObject.tag == "Obstacle")
{
movement.enabled = false;
FindObjectOfType<GameManager>().Endgame();
}
}
}