Object Pooling

Object Pooling is a way to re-use objects without having to re-initialize them. Instead of removing & instantiating an object multiple times, it simply enabled/disabled them, improving performance.

To get started using Object Pooling we need a place to store ALL the objects.

Create a Resources folder anywhere in the project structure. Here we can create a new Pool object. Right-click inside the folder and select Create/Essentials/Pooling/Pool.

If you are creating your own Pool like above, you must remove the Pool in the Pooling/Demo/Resources/Pool or you can just use the same one as the demo.

Now we have created a Pool object that stores all our poolable objects.

There must always be exactly one Pool object in the project.

To actually pool an object we need to extend the APoolable class. We can replace any MonoBehaviour with APoolable to make an object poolable.

public class TestClass : MonoBehaviour { }

Will become:

public class TestClass : APoolable { }

When a poolable object contains multiple MonoBehaviour components or has children that contains MonoBehaviour, you need the other (everything except the poolable class) to inherit the IPoolableFamily interface.

For example; if we have another MonoBehaviour next to the original poolable script:

public class TestSiblingClass : MonoBehaviour, IPoolableFamily { }

When using a poolable object, we must replace Unity's default Awake() and Start() methods with OnAwake() and OnStart(), respectively.

Now that we have converted our object to be poolable we should add it to the Pool. Select the Pool object we created earlier and add a new entry under the Objects tab. Here we can define which object we want to pool and how many of those objects should spawn initially. Drag your poolable prefab onto the Object To Pool and change the Amount To Pool to 10.

If we start our game it should.. not work? We get a warning telling us that the Pool has not been initialized. This is simply because we need to call Pool.Init() whenever we want to start the pooling process. This should usually be done at the start of the game.

We could simply call Pool.Init() in a Awake() method:

public class InitializePool : MonoBehaviour
{
    private void Awake()
    {
        Pool.Init();
    }
}

But, currently it initializes only when this scene is called and it may even lead to you initializing the pool multiple times if the same scene is reloaded. Another, better way, is to initialize it using:

[RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.SubsystemRegistration)]

This ensures that the pool is initialized once, automatically, as soon as the runtime starts — before any scenes are loaded. For more information check out the Unity API.

public class InitializePool
{
    [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.SubsystemRegistration)]
    private static void Initialize()
    {
        Pool.Init();
    }
}

Now, if we run our game again, we can see that the pooling system has spawned a couple of instances of our poolable object in the DontDestroyOnLoad scene.

To instantiate our poolable object we replace Unity's default Instantiate() method with Pool.Acquire():

public class TestSpawnObject : MonoBehaviour
{
    public TestClass obj;
    
    private void Start()
    {
        // Instantiates our object & assigns it to a variable
        TestClass copy1 = (TestClass)Pool.Acquire(obj, transform.position, Quaternion.identity);
        // Instantiates our object again, this time it doesn't assign it to any variable
        Pool.Acquire(obj, transform.position, Quaternion.identity);
    }
}

To later destroy our poolable object we replace Unity's default Destroy(poolable) method with poolable.Dispose():

public class TestSpawnObject : MonoBehaviour
{
    public TestClass obj;
    
    private void Start()
    {
        // Instantiates our object & assigns it to a variable
        TestClass copy = (TestClass)Pool.Acquire(obj, transform.position, Quaternion.identity);
        // "Destroys" the object (disables it for later use)
        copy.Dispose();
    }
}