Script working properly on one gameobject, but not on another

Question

I have a very strange problem.

I created an AI using the navmesh tools and a custom script which keeps assigning a new destination to the navmesh agent once the old destination is reached.

I had to replace the model for this AI (was a capsule before), so I did that, copied almost all components, adjusted a few parameters like agent height etc., and ran it.

The capsule AI does its job properly, but the AI with the correct model clearly doesn't.
After debugging, I discovered that the List of destinations for the modelled AI consists if Vector3.zero's, while the capsule AI has the correct vector3s in its destination list.

Here's my AI destination script:

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

public class AIMovement : MonoBehaviour
{

private NavMeshAgent _navMeshAgent;                         //reference to the navmesh agent
private MapController _mapControllerScript;                 //reference to the map controller script to access waypoints
private List<Vector3> _wayPoints = new List<Vector3>();
private Vector3 _destination;

// Use this for initialization
void Start()
{
    _mapControllerScript = GameObject.Find("Map_01").GetComponent<MapController>();
    SetWayPointLocations();
    _navMeshAgent = this.GetComponent<NavMeshAgent>();

    Debug.Log(_mapControllerScript.ToString());
    Debug.Log(_mapControllerScript.HealthPickUpPositions.ToString());
    Debug.Log(_navMeshAgent);
    Debug.Log(_wayPoints);
    foreach (Vector3 waypoint in _wayPoints)
    {
        Debug.Log(waypoint);
    }
}

// Update is called once per frame
void Update()
{
    MoveAroundMap();
}

void MoveAroundMap()
{
    if (_navMeshAgent.transform.position.x == _destination.x &&
        _navMeshAgent.transform.position.z == _destination.z
        || _destination == new Vector3(0, 0, 0)
        )
    {
        Debug.Log("Acquiring new position");
        _destination = _wayPoints[Random.Range(0, _wayPoints.Count-1)];
    }

    _navMeshAgent.SetDestination(_destination);
}

void SetWayPointLocations()
{
    foreach (Vector3 waypoint in _mapControllerScript.HealthPickUpPositions)
    {
        _wayPoints.Add(waypoint);
    }
    foreach (Vector3 waypoint in _mapControllerScript.AmmoPickUpPositions)
    {
        _wayPoints.Add(waypoint);
    }
}
}

Here's the console: you can clearly see the coordinates of the capsule AI being correct, while the coordinates of the broken AI being (0, 0, 0).

Here's the hierarchy window: Capsule is the working AI, Character_Piccolo the non-working.

Here's the inspector of the Capsule, the working AI.

Here's the inspector of the model, the broken AI.

Sorry for making this long, but I wanted to make sure you guys had all the needed information.

Thanks in advance!

Answer 1

The problem - and also the solution - are not in your AIMovement script, or in any edit you did while changing from the capsule to you new model, not even in any of the scripts and components you provided in the question. The problem is a subtlety in you MapController class that was already there all the time (even before your changes), and the fact that you did not experience this error before is a matter of casuality.

As you said in the comments, you're setting up HealthPickUpPositions and AmmoPickUpPositions properties of you MapController class in its Start() method. And you're reading the values of those properties on the Start() method of your component class. The thing is: the Start message runs once a gameObject is set on a loaded scene, but the order in that objects get started does not depend on your game logic (it depends on the scene hierarchy, prefabs, object instance number and other stuff, whatever...) and should be considered random.

In your specific case, the Start() of your AIMovement is being called before the Start() of MapController, i.e. before the proper values of the properties being set - hence, all you read are zero-vectors (default values).

Because of that, unity has a similar message named Awake() on gameObjects. You also don't know the order in which the objects will be awoken, but you can assure that any Start() message will be sent only after all the Awake() messages were already been sent. More on this here, here, here and here.

The solution: Put all internal initialization logic of your classes in the Awake method; and all the connections to other gameobjects (that assume they are initialized) on the Start method.