Spawned Enemies: How to Destroy child objects inside their own attached scripts without Destroying the parent object for InvokeRepeating??

Question

I'm creating a (early version) tower defense shooter game with spawned enemies. I have GameObject called SpawnLocation that contains the location in w$$anonymous$$ch I would like to spawn my enemies, with a EnemyManager.cs script attached to it. In that, I call InvokeRepeating ("Spawn", 3f, 3f) in my Start(), and in Spawn(), I call Instantiate (enemy, transform.position, transform.rotation) (enemy being the game object prefab). Attached to that enemy prefab, I have an EnemyController.cs script w$$anonymous$$ch detects collisions and Destroy(gameObject).

When I destroy the first enemy, however, I receive an error preventing further spawns:

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

I believe it is because since I passed in my enemy object, destroying itself after instantiation in its own separate function still destroys the parent object passed in, w$$anonymous$$ch means if I try to invokerepeat with that destroyed object, I'll have no object to instantiate. So how do I go about t$$anonymous$$s?

I've been frustratingly searc$$anonymous$$ng for an answer for aw$$anonymous$$le but couldn't find one specific to destroying multiple c$$anonymous$$ld game objects wit$$anonymous$$n their own instantiated scripts. I know Instantiate() returns the clone object when called in the parent, but how do I destroy it from that other attached c$$anonymous$$ld function, not the parent function? Deactivate() likely does the same t$$anonymous$$ng. If I instead Destroy() inside the parent function, how do I get the clone object if that object does not have a distinctive ID (and its position moves)? Using an array of enemy clone objects doesn't really allow me to know if it's been $$anonymous$$t 10 (or however many) times and needs to be destroyed. I've tried using coroutines, but seemed to run into problems as well. Here's a sample code:

 public class EnemyManager : MonoBehaviour {
     public GameObject enemy;
     public int playerHealth, spawnCount, deathCount, numEnemies;
 
     void Start() {
         numEnemies = playerHealth = spawnCount = 10;
         deathCount = 0;
 
         InvokeRepeating("Spawn", 3f, 3f); //give some time before spawning
     }
 
     void Update() {
     if(playerHealth <= 0)
         //end game somehow
     }
 
     void Spawn() {
         if(playerHealth <= 0 || deathCount >= numEnemies)
             return;
 
         Instantiate(enemy, transform.position, transform.rotation);
         spawnCount += 1; // keeps track of number of enemies spawned
     }
 }
 
 public class EnemyController : MonoBehaviour {
     public int enemyHealth;
 
     void Start() {
         enemyHealth = 10; //$$anonymous$$t each enemy 10 times to destroy it
         manager = GameObject.Find ("Spawn Location");
         managerScript = manager.GetComponent<EnemyManager>();
     }
 
     void Update() {
         //move player on a path
         if(enemyHealth <= 0) {
             managerScript.deathCount += 1; //successful kill of an enemy
             Destroy(gameObject); //or deactivate
         }
     }
 
     void OnTriggerEnter2D(Collider2D other) {
         if(other.gameObject.CompareTag("Bullet")) { //many triggers on board
             enemyHealth -= 1;
         }
         else if(other.gameObject.CompareTag("EndPath")) {
             managerScript.playerHealth -= 1;
             Destroy(gameObject); //so it doesn't keep on walkin forever
         }
     }
 }

Answer 1

Answer by LiamofElites · Feb 14, 2018 at 12:33 PM

Here are a few t$$anonymous$$ngs that I would do that might help you with your code logic,

in the OnTriggerEnter2D in the first if statement ( if(other.gameObject.CompareTag("Bullet")) ) after enemyHealth -= 1 add the if(enemyHealth <= 0) block after that line so right after taking damage you'll check if there's no health left instead of always checking in the update method

When declaring manager in the EnemyController class use gameObject.transform.parent.gameObject so if you want to create more spawn locations you don't have to worry about being limited to only 1 because you're using GameObject.Find();

I hope t$$anonymous$$s helps you somewhat, I'll be experiementing with your code in my practice project.

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changled · Feb 14, 2018 at 07:54 PM 0

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Thank you for your response. I think checking for enemyHealth is a great idea and good practice.

In regards to the second part, my problem isn't being able to spawn in different locations, but how to destroy each of those children after they die (aka their individual health reaches zero) without destroying the original game object used to continue spawning new enemies! Because in EnemyController, as soon as I call Destroy(gameObject), I seem to have an effect on the spawning capabilities of the parent going on at the same time. As I continued testing yesterday, I realized that Destroy()-ing the first enemy created will only produce me 4 enemies in total (aka it'll stop instantiating new children), likely because that's how long it took me to destroy the first enemy.

changled · Feb 14, 2018 at 07:57 PM 0

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IN FACT, I put a Debug.Log("Enemy Spawned"); print right before the Instantiate() call in Spawn(), and I only get that log starting from the second enemy spawned!! This makes me suspect that the first time either Instantiate() or InvokeRepeating() is called, that first Instantiate() is called immediately with the actual GameObject passed in, and THEN the following Instantiate() calls return instances/clones of that original GameObject?? Not sure if I'm explaining this correctly.

Spawned Enemies: How to Destroy child objects inside their own attached scripts without Destroying the parent object for InvokeRepeating??

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