Unity 3D- The "Is Trigger" Under Sphere Collider Is not allowing my fireball/projectile to fly

Question

I am reading this book about Unity (dated 2018) and it instructed me to click on that "Is Trigger?" box under the Sphere Collider section of the Inspector.

When I don't click it, the projectile flies just fine. But when I click it, it is just stuck at the starting point of the game object.

Here is the projectile code:

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

public class Fireball : MonoBehaviour
{
    public float speed = 10.0f;
    public int damage = 1;
    // Start is called before the first frame update
    
    // Update is called once per frame
    void Update()
    {
        transform.Translate(0, 0, speed * Time.deltaTime);
    }

    void OnTriggerEnter(Collider other)
    {
        PlayerCharacter player = other.GetComponent<PlayerCharacter>();
        if (player != null)
        {
            player.Hurt(damage);
        }
        Destroy(this.gameObject);
    }

}

Here is the accompanied code attached to the enemy:

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

public class WanderingAI : MonoBehaviour
{
    public float speed = 3.0f;
    public float obstacleRange = 5.0f;
    private bool _alive;

    [SerializeField] private GameObject fireballPrefab;
    private GameObject _fireball;

    void Start()
    {
        _alive = true;    
    }

    // Update is called once per frame
    void Update()
    {
        if (_alive)
        {
            transform.Translate(0, 0, speed * Time.deltaTime);

            Ray ray = new Ray(transform.position, transform.forward);
            RaycastHit hit;
            if (Physics.SphereCast(ray, 0.75f, out hit))
            {
                GameObject hitObject = hit.transform.gameObject;
                if (hitObject.GetComponent<PlayerCharacter>())
                {
                    if (_fireball == null)
                    {
                        _fireball = Instantiate(fireballPrefab) as GameObject;
                        _fireball.transform.position = transform.TransformPoint(Vector3.forward * 1.5f);
                        _fireball.transform.rotation = transform.rotation;
                    }
                }

                else if (hit.distance < obstacleRange)
                {
                    float angle = Random.Range(-110, 110);
                    transform.Rotate(0, angle, 0);
                }
            }
        }
    }

    public void SetAlive(bool alive)
    {
        _alive = alive;
    }
}

And I need to click that "is trigger?" box, otherwise my projectile would just lie on the floor and not doing anything after it hits a wall.

I don't think the problem is with the code itself but with newer updates to Unity after 2018 that I am not familiar with (since I basically just started using Unity like two weeks ago).

I am guessing that I should create the trigger on the C# Script itself and not rely on that check box.

Can anyone verify this and help me out how to apply that code?

Thanks in advance.

Answer 1

Please refer to Colliders -> Collision Action Matrix

=> If none of your objects is a trigger then OnTriggerEnter is never called and you might rather want to go for OnCollisionEnter

---

Also in general as soon as you are dealing with physics (Rigidbody, Rigidbody2D) you do not want to transform your objects using the Transform component!

Instead of

void Update()
{
    transform.Translate(0, 0, speed * Time.deltaTime);
}

you should rather do

[SerializeField] private Rigidbody _rigidbody;

private void Awake()
{
    if(!_rigidbody) _rigidbody = GetComponent<Rigidbody>();

    _rigidbody.velocity = _rigidbody.rotation * Vector3.forward * speed;
}

and let the physics engine handle the movement itself.