Unity - Object Pooling Reference

Using UnityEngine.ObjectPool

This is a technique I learnt from this youtube video.

public class BulletHellManager: Singleton<BulletHellManager> {
    ObjectPool<Bullet> bulletPool;
    readonly List<Bullet> activeProjectiles = new List<Bullet>();
    readonly List<Bullet> bulletsToReturn = new List<Bullet>();

    void Start() {
        bulletPool = new ObjectPool<Bullet>(
            createFunc: () => {
                GameObject bulletObj = Instantiate(bulletPrefab, bulletOrigin.transform, true);
                bulletObj.SetActive(false);
                return bulletObj.GetOrAdd<Bullet>();
            },
            actionOnGet: bullet => bullet.gameObject.SetActive(true),
            actionOnRelease: bullet => bullet.gameObject.SetActive(false),
            actionOnDestroy: bullet => Destroy(bullet.gameObject),
            collectionCheck: false,
            defaultCapacity: bulletCount,
            maxSize: bulletCount * 10
        )
    }

    void Update() {
        for (int i = 0; i < activeProjectiles.Count; i++) {
            Bullet bullet = activeProjectiles[i];
            if (bullet.HasTravelledMaxDistance()) {
                ReturnBullet(bullet);
            }
        }
    }

    void LateUpdate() {
        foreach (var bullet in bulletsToReturn) {
            bulletPool.Release(bullet);
        }
        bulletsToReturn.Clear();
    }

    void OnDestroy() {
        bulletPool.Dispose();
    }

    void ReturnBullet(Bullet bullet) {
        bulletsToReturn.Add(bullet);
        activeProjectiles.Remove(bullet);
    }

    public void SpawnBullet() {
        Bullet bullet = bulletPool.Get();
        bullet.Init(); // way to implement the direction to fly
        activeProjectiles.Add(bullet);
    }
}

Using Simple Scripts

Referencing Unity’s Introduction to Object Pooling, we can use the following scripts to manually control our instantiated objects using List.

public static ObjectPool SharedInstance;
public List<GameObject> pooledObjects;
public GameObject objectToPool;
public int amountToPool;

void Awake()
{
    SharedInstance = this;
}

void Start()
{
    pooledObjects = new List<GameObject>();
    GameObject tmp;
    for(int i = 0; i < amountToPool; i++)
    {
        tmp = Instantiate(objectToPool);
        tmp.SetActive(false);
        pooledObjects.Add(tmp);
    }
}

public GameObject GetPooledObject()
{
    for(int i = 0; i < amountToPool; i++)
    {
        if(!pooledObjects[i].activeInHierarchy)
        {
            return pooledObjects[i];
        }
    }
    return null;
}

To use the object pool, use this

GameObject bullet = ObjectPool.SharedInstance.GetPooledObject(); 
  if (bullet != null) {
    bullet.transform.position = turret.transform.position;
    bullet.transform.rotation = turret.transform.rotation;
    bullet.SetActive(true);
  }

unity ref