Spawning Enemy issue

Question

I'm trying to have my game spawn enemies when ever the player reaches a way point.

Right now, I have this functionality working. When my player gets to the first way, the enemies spawn. He only moves on once he has killed all of the enemies on the screen are dead. However, when he gets to the second way point, no enemies spawn.

Right now, in my collision class I call the following line of code:

Destroy(gameObject)

Whilst this work for the first way point, the second one wont spawn anything as the game object my collision class has been attached to has been destroyed. However, all of my enemies are prefabs and I thought the destroy function would only destroy that instance of the prefab. No matter when you called the instantiate method, it would only destroy that instance.

I'm spawning my enemies with the following method:

  public GameObject SpawnEnemies()
{
    Vector3 _position = new Vector3(transform.position.x, transform.position.y, transform.position.z);

    // instantiate particel system
    Instantiate(_particle, _position, Quaternion.identity);


    _clone = (GameObject)Instantiate(_enemy, _position, transform.rotation);
    _ai = _clone.GetComponent<HV_BaseAI>();
    _ai._waypoints = _wayPoints;

    return _clone;
}

Then I'm finding out how many of the enemies are still alive with the following code in my collision method:

  GameObject g, f; // enemies I want to spawn
    g = GameObject.FindGameObjectWithTag("SectionController");
    f = GameObject.FindGameObjectWithTag("SectionController");

    HV_SectionController tempSectionControllerGroundEnemies, tempSectionControllerFlyingEnemies;
    tempSectionControllerGroundEnemies = g.GetComponent<HV_SectionController>();
    tempSectionControllerFlyingEnemies = f.GetComponent<HV_SectionController>();

    tempSectionControllerGroundEnemies._numberOfGroundEnemies.Remove(gameObject); // remove enemies from list
    tempSectionControllerFlyingEnemies._numberOfFlyingEnemies.Remove(gameObject);
    //Destroy(gameObject);



    _numberOfGroundEnemies = tempSectionControllerGroundEnemies._numberOfGroundEnemies.Count;
    _numberOfFlyingEnemies = tempSectionControllerFlyingEnemies._numberOfFlyingEnemies.Count;

Then when I want to move on I do the following check:

 if (_groundEnemiesRemaining == 0)
        {
            MoveToNextSection();
            _sectionStartTime = Time.time;
        }

i know the above line is checking only one type of enemy at the moment, but its the ground enemies I'm having issues with at the moment.

Does anyone know how I can delete the enemy prefab I'm spawning from my first section, once they've been hit, then have it respawn at the next section without the error:

The object of type 'GameObject' has been destroyed but you are still trying to access it.

Where do you initiate gameObject? Where do you delete/destroy them? — Joetjah
I instantiate my gameObject in a class called SpawnGroundEnemy class and I destroy them in my EnemeyDeath class — N0xus
Well, it is obvious you try to access 'GameObject' while it's destroyed. I can't see the code where you create and destroy it, and I'm sure this isn't all the code that uses that 'GameObject'. I can't find the error through the code that is provided... — Joetjah

Steven Mills Steven Mills · Accepted Answer · 2013-03-27T11:23:59

My guess would be that the gameobjects are being "destroyed" by two different collision events. First one destroys it, second throws the error.

What I've done in similar situations is put the Destroy code within the object being destroyed. Then from within your collision class, use gameObject.SendMessage(string) to send a message to the actual object, which destroys it.

Without seeing further code I can't speculate as to the origin of the error, but the above is my best guess. SendMessage can also take a DontRequireReceiver parameter, so it won't pop an error if two collision events try to send it a message.

Spawning Enemy issue

2 Answers