Powerup only spawning twice (MissingReferenceException Error)

Questions & Answers
1

So in my game I have an object that the powerup Spawns on top of (I intend for you to have to activate it to get the powerup but for now you just walk over it, but that’s not the problem), I have it so on Start a powerup spawns, then five seconds after the powerup has worn off a new one spawn, that first cycle works fine, but after I pick up the new one, instead of spawning in the new one I get this error:

MissingReferenceException: The object of type ‘Powerup’ has been destroyed but you are still trying to >access it.
Your script should either check if it
is null or you should not destroy the
object. Powerup.Remove () (at
Assets/Scripts/Powerup/Powerup.cs:30)
Powerup.m__0 () (at
Assets/Scripts/Powerup/Powerup.cs:11)
PowerupController+c__Iterator0.MoveNext
() (at
Assets/Scripts/Powerup/PowerupController.cs:37)
UnityEngine.SetupCoroutine.InvokeMoveNext
(IEnumerator enumerator, IntPtr
returnValueAddress) (at
C:/buildslave/unity/build/Runtime/Export/Coroutines.cs:17)

PowerupWellController Class:

public class PowerupWellController : MonoBehaviour {
	public Color color;
	public GameObject powerup;

	private bool powerupSpawned;
	private bool powerupSpawning;
	private string powerupName;

	// Use this for initialization
	void Start () {
		powerupName = powerup.name.Substring (8, powerup.name.Length - 8);
		SpawnPowerup ();
		color = powerup.GetComponent<SpriteRenderer> ().color;
	}
	
	// Update is called once per frame
	void Update () {
		if(transform.childCount == 0){
			powerupSpawned = false;
		}

		if(!powerupSpawned && !powerupSpawning){
			powerupSpawning = true;
			Debug.Log ("Spawning Powerup!");
			StartCoroutine (PowerupController.CallAfterTime (SpawnPowerup, 5f));
		}
	}

	void OnTriggerStay2D (Collider2D col){
		if(col.gameObject.name == "Player"){
			if(col.gameObject.GetComponent<PlayerController>().activate){
				col.gameObject.GetComponent<SpriteRenderer> ().color = color;
			}
		}
	}

	private void SpawnPowerup(){
		PowerupController.SpawnPowerup (powerupName, new Vector2(gameObject.transform.position.x, gameObject.transform.position.y + 0.75f), this.transform);
		powerupSpawned = true;
		powerupSpawning = false;
	}
}

Powerup Class:

public class Powerup : MonoBehaviour {
	public Effect effect;

	public void OnPickup(){
		effect.action ();

		effect.endAction += delegate{ Remove(); };

		StartCoroutine (PowerupController.CallAfterTime(effect.endAction, effect.length));
	}

	void OnTriggerEnter2D(Collider2D c){
		if(c.transform.tag == "Player"){
			OnPickup ();
			Disable ();
		}
	}

	private void Disable(){
		GetComponent<Collider2D> ().enabled = false;
		GetComponent<SpriteRenderer> ().enabled = false;
	}

	private void Remove(){
		Debug.Log ("Remove() Called!");
		Destroy (gameObject);
	}
}

The Remove function in the Powerup class does get called, it just doesn’t seem to destroy the second powerup after it wears off like it’s supposed to.

2

so whats happening here and we can kind of see this based on the error thrown is this error is specifically saying your trying to destroy an already destroyed object.

so what i can tell you is the second attempt at calling removing is in fact still calling the first powerups code/script.

my guess is the problem is something to do with this line and the code in here.

 PowerupController.SpawnPowerup (powerupName, new Vector2(gameObject.transform.position.x, gameObject.transform.position.y + 0.75f), this.transform)

somehow your not really creating a new powerup (i.e. using new keyword) but your somehow storing a reference to the old.

so your trying to destroy the same object twice instead of two seperate objects is the problem if that helps. This is generally caused by you somewhere saying something like

powerupreference = powerup

powerup.destory()

and not then going and after you destroy doing something like

poweruprefrence = null;
or making sure when you pick up the second powerup you change the reference.

somewhere you keeping and storing the reference to the first object and never getting rid of it so at some point your calling

powerup.remove() and the powerup variable that your using is still the old one and hasn’t been updated to be the second powerup.

3

I fixed it, basically what I did was instead of calling the Remove() function and destroying that specific gameObject, I made a new function in my WellController that cleared all child objects of that well.

Thank you for the help sparkzbarca!