Destroy prefabs after they have been instantiated (C#)

Question

Hello my friend who is reading this! I got a problem with some of my code. I have created a power up prefab that is supposed to destroy all enemy prefabs that are out on the map. I'm spawning out new enemies every 3 to 5 seconds. Now when I run over the power up, it only destroys the enemies that were instantiated before the power up was used and spawned.

How can I destroy all enemies out on the map including the new ones that spawned in after the power up spawns in?

Code for picking up the power up: (Note that the power up is used directly when you trigger/collide with it)

 using UnityEngine;
 using System.Collections;
 
 public class PickUpScript : MonoBehaviour 
 {
     void OnTriggerEnter2D(Collider2D col)
     {
         if(col.gameObject.tag == "PowerUp1")
         {
             Destroy(GameObject.FindGameObjectWithTag("EnemyBouncing"));
             Destroy(GameObject.FindGameObjectWithTag("EnemyFollow"));
             Destroy(GameObject.FindGameObjectWithTag("PowerUp1"));
         }
 }

Code for spawning out enemies:

 using UnityEngine;
 using System.Collections;
 
 public class EnemySpawn : MonoBehaviour 
 {
     // EnemyPrefabs
     public GameObject EnemyBouncingPrefab;
     public GameObject EnemyFollowPrefab; 
 
     //Show where spawn is prefab
     public GameObject ShowEnemySpawn;
 
     // Array of spawn points 
     public Transform[] spawnPoints;         
     
     // Borders
     public Transform borderTop;
     public Transform borderBottom;
     public Transform borderLeft;
     public Transform borderRight;
 
 
 
     void Start () 
     {
         // Starts a coroutine function for spawning bouncing enemies
         StartCoroutine(SpawnBouncingEnemy());
 
         // Spawn only one follow enemy
         InvokeRepeating("SpawnEnemyFollow", Random.Range(2, 5), 0);
     }
 
     
     // Spawn a Bouncing enemy
     IEnumerator SpawnBouncingEnemy() 
     {
         //Wait 3 seconds when game starts to spawn a ball
         yield return new WaitForSeconds(Random.Range(3, 5));
 
         while(true)
         {
             //Calls the function to set random position
             Vector2 spawnPoint = RandomPointWithinBorders();
             
             // Show spawn location for one second
             Object marker = Instantiate(ShowEnemySpawn, spawnPoint, Quaternion.identity);
             yield return new WaitForSeconds(1);
             Destroy(marker);
             
             // Spawn enemy
             Instantiate(EnemyBouncingPrefab, spawnPoint, Quaternion.identity);
             yield return new WaitForSeconds(Random.Range(4, 6));
         }
         
     }    
 
     Vector2 RandomPointWithinBorders()
     {
         //Code that will spawn a bouncing ball and ShowSpawn at a random position inside the borders 
         Vector2 random = new Vector2();
         random.x = (int)Random.Range(borderLeft.position.x, borderRight.position.x);
         random.y = (int)Random.Range(borderBottom.position.y, borderTop.position.y);
         return random;
     }
 
 
     void SpawnEnemyFollow()
     {
         // Find a random index between zero and one less than the number of spawn points.
         int spawnPointIndex = Random.Range (0, spawnPoints.Length);
 
         
         // Create an instance of the enemy prefab at the randomly selected spawn point's position and rotation.
         Instantiate (EnemyFollowPrefab, spawnPoints[spawnPointIndex].position, spawnPoints[spawnPointIndex].rotation);
     }
 }

I'm so grateful for every help that I can get! You guys are the best! Been trying to solve this for ages, but haven't found any great answers yet.

Answer 1

Instead of using the tag system, you might want to just keep track of your spawned enemies:

 using System.Collections.Generic;

So we'll just add new enemies to a list:

 // Keep track of enemies we've created across all spawners
 public static List<GameObject> activeEnemies;
 
 // Start
 void Awake()
 {
     // Create the list
     activeEnemies = new List<GameObject>();
 }
 
 // Destroy all existing enemies
 public static void DestroyActiveEnemies()
 {
     // Prevent ourselves from tinkering with a List during its enumeration
     int currentCount = activeEnemies.Count;
 
     // Go through and destroy each one
     for (int k=0; k<currentCount; k++)
     {
         Destroy(activeEnemies[k]);
     }
 
     // Clear the list up to this point
     activeEnemies.RemoveRange(0, currentCount);
 }

So for each of your spawning functions, add the new enemy to this list:

 // Instantiate
 GameObject newEnemy = (GameObject) Instantiate(EnemyBouncingPrefab, spawnPoint, Quaternion.identity);
 
 // Add them to our list
 activeEnemies.Add(newEnemy);
 
 // Yield for the coroutine (Note that this will cause GC (due to the "new" part),
 // but you can declare a WaitForSeconds instance to prevent this
 yield return new WaitForSeconds(Random.Range(4, 6));

Causing your pickup script's Trigger code to become:

 public class PickUpScript : MonoBehaviour 
 {
     void OnTriggerEnter2D(Collider2D col)
     {
         if(col.gameObject.tag == "PowerUp1")
         {        
             // Call the function we just wrote
             EnemySpawn.DestroyActiveEnemies();
         }
     }
 }

Destroy prefabs after they have been instantiated (C#)

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