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ObjectPool / AsyncObjectPool

This sample show how to use ObjectPool, though not a native part of UniRx but useful. (AsyncObjectPool is most same as ObjectPool except it works asyncronously)

Note you need Unity 5.4.x or newly version than it to use ObjectPool or AsyncObjectPool.

EnemyObjectPool

First, make a classs which derives ObjectPool and override 'CreateInstance()' for its method.

public class EnemyObjectPool : ObjectPool<Transform>
{
    // A gameobject which to be instantiated.
    public GameObject EnemyPrefab;

    // to keep created instance under the parent gameobject in the hierarchy.
    protected Transform parent;

    public EnemyObjectPool(Transform _parent)
    {
        parent = _parent;
    }

    protected override Transform CreateInstance()
    {
        Transform tm = GameObject.Instantiate(EnemyPrefab).GetComponent<Transform>();
        if (parent != null)
            tm.transform.SetParent(parent);

        return tm;
    }

Note, for a generic type of the parent class, ObjectPool<T>, only UnityEngine.Component derived class can be possible as its type.

Also there are other methods can be overrided if it is neccessary.

Note instance.gameObject.SetActive(true) is called inside of OnBeforeRent() and instance.gameObject.SetActive(false) is called for OnBeforeReturn().

// Override, if you have somethiing to do before you rent an object from a pool.
protected override void OnBeforeRent(Transform instance)
// Override, if you have somethiing to do before you return an object back to a pool.
protected override void OnBeforeReturn(Transform instance)
// Override, if you have somethiing to do when on emptying a pool.
protected override void OnClear(Transform instance)

Note OnClear is also called inside of Shrink and StartShrinkTimer.

Instantiate Pool

Instantiate 'ObjectPool' instance and set GameObject which to be intantiated within the pool.

pool = new EnemyObjectPool(this.gameObject.transform);
pool.EnemyPrefab = enemyPrefab;

Use 'Rent' to get an object from pool.

Transform tm = pool.Rent ();

Note, use 'RentAsync' instead of 'Rend' if you derived AsyncObjectPool instead of ObjectPool.

Also you can preload an object of a pool with 'PreloadAsync'.

pool.PreloadAsync(10, 1).Subscribe(_ => { Debug.Log("Done Preloading"); });

Note the above code creates each object per a one frame and inserts it into the pool by number of ten.

If an object is no longer needed, back it to the pool with 'Return'.

pool.Return (tm);

Empty Pool

You can empty the pool with 'Clear' and the pool has no object inside of it.

pool.Clear ();

Note 'Clear' destroy all objects in a pool.

Shrink and StartShrinkTImer

'ObjectPool' of UniRx provides any other convenient methods based on power of Rx. 'Shrink' is one of them.

Use 'Shrink' if you want to decrease number of object in a pool.

pool.Shrink(0.6f, 4);

After shrinking, the pool remains 60% of object but keep four as its minimum.

There is also another method to shrink size of a pool, 'StartShrinkTimer' which shrinks size of a pool as like 'Shrink' does but it reduces per a given time.

IDisposal disposal  = pool.StartShrinkTimer(System.TimeSpan.FromSeconds(2), 0.4f, 3);

The above code shrink up to 40% for every two second until the number of object in the pool is three.

If you want to stop shrinking on the way of its progress, use 'Dispose' same as like other UniRx's object.

disposable.Dispose ();