use of gameObject in MonoBehaviour script leads to NullReferenceException

[ashen delta]

Hi there, I am new to unity and C#, but I am not new to programming.

I got this error when trying to pass gameObject to a method call like like this:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class AbilityHandler : MonoBehaviour
{
    public Ability ability;
    // Update is called once per frame
    void Update()
    {

          if (Input.GetKeyDown(key))
                {
                    ability.Activate(gameObject); //<-- error points to this
                }
    }
}

The method that I am calling is from this:

public class Ability : ScriptableObject
{
    public new string name;
    public float cooldownTime;
    public float activeTime;

    public virtual void Activate(GameObject parent){}
}

And I am getting this error:

I was under the impression that gameObject can be referenced anywhere in a MonoBehaviour script

[halcyon monolith]

gameObject is not causing the exception.

ability is probably null.

gameObject could cause an exception if you tried to access it from a destroyed component

but since you're in Update, that seems very unlikely

(unity isn't going to call Update on a destroyed component)

[ashen delta]

ability shouldnt be null, I am passing in this right here:

This is the video that I am following
https://www.youtube.com/watch?v=ry4I6QyPw4E

Ok I think I figured it out

I think it has something to do with the activate method in Teleport

This is what I had:

    public override void Activate(GameObject parent)
    {
        // teleport towards the mouse cursor position by teleportDistance

        // get the mouse position in world coordinates
        Vector3 mousePosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        // get the direction from the player to the mouse
        Vector3 direction = mousePosition - parent.transform.position;
        // normalize the direction vector
        direction.Normalize();
        // multiply the direction vector by the teleportDistance
        direction *= teleportDistance;
        // add the direction vector to the player's position
        Vector3 newPosition = parent.transform.position + direction;
        // set the player's position to the new position
        parent.transform.position = newPosition;
    }

But when I comment it out, it no longer gives me an error

[halcyon monolith]

Oh, right, Teleport.Activate would be the ability's Activate method

[halcyon monolith]

The error doesn't point there -- it poinst to Activate

so, which is line 14?

[ashen delta]

That is line 14, the reason its not line 14 in the example I gave is cause I got rid of a bunch of variables that arent relevant, to make it easier to read

[halcyon monolith]

Do not remove anything from your code.

That just makes it harder to understand what's happening.

Please share the entire script. I need a clear picture of what's happening here.

!code

[opaque sapphire]

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[ashen delta]

Sure my bad

// AbilityHandler.cs
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class AbilityHandler : MonoBehaviour
{
    public Ability ability;
    float cooldownTime;
    float activeTime;

    enum AbilityState
    {
        Ready,
        Active,
        Cooldown,
    }

    private AbilityState state;

    public KeyCode key;


    // Update is called once per frame
    void Update()
    {
        switch (state) {
            case AbilityState.Ready:
                if (Input.GetKeyDown(key))
                {
                    ability.Activate(gameObject);
                }
                break;
            case AbilityState.Active:
                if (activeTime > 0)
                {
                    activeTime -= Time.deltaTime;
                }
                else
                {
                    state = AbilityState.Cooldown;
                    cooldownTime = ability.cooldownTime;
                }
                break;
            case AbilityState.Cooldown:
                if (cooldownTime > 0)
                {
                    cooldownTime -= Time.deltaTime;
                }
                else
                {
                    state = AbilityState.Ready;
                }
                break;

        }
    }
}

// Ability.cs
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Ability : ScriptableObject
{
    public new string name;
    public float cooldownTime;
    public float activeTime;

    public virtual void Activate(GameObject parent){}
}

// Teleport.cs
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[CreateAssetMenu]
public class Teleport : Ability
{
    public float teleportDistance;
    public override void Activate(GameObject parent)
    {
        // teleport towards the mouse cursor position by teleportDistance

        // get the mouse position in world coordinates
        Vector3 mousePosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        // get the direction from the player to the mouse
        Vector3 direction = mousePosition - parent.transform.position;
        // normalize the direction vector
        direction.Normalize();
        // multiply the direction vector by the teleportDistance
        direction *= teleportDistance;
        // add the direction vector to the player's position
        Vector3 newPosition = parent.transform.position + direction;
        // set the player's position to the new position
        parent.transform.position = newPosition;
    }
}

[halcyon monolith]

is this line 14?

Vector3 mousePosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);

or, more importantly, is this the line that the exception is coming from?

[ashen delta]

yeah I think so

My bad I should of gone there initially, when I clicked on the error, it sent me to the other line

[halcyon monolith]

I dunno why unity does that

I think it's trying to avoid showing you library code

but it just dumps you in a bogus location instead

you can click the links in the stack trace to jump to the correct line

so, this means that Camera.main is null

is your camera object tagged MainCamera?

[ashen delta]

I think so

actually no

That fixed it ty!

[halcyon monolith]

https://unity.huh.how/runtime-exceptions/nullreferenceexception

some good reading on this kind of error

np!

[ashen delta]

This is probably not the best way to teleport the player towards the mouse anyways, a bit janky. But now I know what I need to fix ty!

[halcyon monolith]

one tip: if you have a rigidbody on the player, you should set its position, rather than messing with the transform's position directly

dunno how your game works though