General trigger for detecting collisions

TriggerVolume.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

[RequireComponent(typeof(Collider))]
/// <summary>
/// General purpose trigger volume system
/// 
/// </summary>
/// <author>Bruno Mikoski</author>
public class TriggerVolume : MonoBehaviour
{
    [SerializeField]
    private LayerMask collisionMask = -1;

    private new Collider collider;
    private List<Collider> containing;
    public event TriggerChangeHandler TriggerExitEvent;
    public event TriggerChangeHandler TriggerEnterEvent;
    public event TriggerChangeHandler TriggerStayEvent;
    public int ContainCount { get { return containing.Count; } }
    public delegate void TriggerChangeHandler(TriggerVolume volume, Collider collider);


    private void Awake()
    {
        containing = new List<Collider>();
        collider = GetComponent<Collider>();
        collider.isTrigger = true;
    }
    public void SetCollisionMask(LayerMask targetLayerMask)
    {
        collisionMask = targetLayerMask;
    }

    public void ToggleVolume(bool enable)
    {
        if (enable)
            collider.enabled = true;
        else
            Disable();
    }

    private void Disable()
    {
        collider.enabled = false;

        if (TriggerExitEvent == null)
            return;

        for (int i = 0; i < containing.Count; i++)
        {
            Collider target = containing[i];
            containing.RemoveAt(i);
            i--;

            TriggerExitEvent(this, target);
        }
    }

    public Collider GetContaining(int index)
    {
        return containing[index];
    }

    public bool Contains(Collider other)
    {
        return containing.Contains(other);
    }

    public void OnTriggerEnter(Collider other)
    {
        if (!IsInLayerMask(other.gameObject))
            return;

        if (!containing.Contains(other))
        {
            containing.Add(other);
            if (TriggerEnterEvent != null)
                TriggerEnterEvent(this, other);
        }
    }

    public void OnTriggerExit(Collider other)
    {
        if (!IsInLayerMask(other.gameObject))
            return;

        containing.Remove(other);
        if (TriggerExitEvent != null)
            TriggerExitEvent(this, other);
    }

    public void OnTriggerStay(Collider other)
    {
        if (!IsInLayerMask(other.gameObject))
            return;

        if (!containing.Contains(other))
            return;

        if (TriggerStayEvent != null)
            TriggerStayEvent(this, other);
    }


    private bool IsInLayerMask(GameObject targetGameObject)
    {
        return ((collisionMask.value & (1 << targetGameObject.layer)) > 0);
    }

#if UNITY_EDITOR
    private void OnDrawGizmos()
    {
        if (containing != null)
        {
            for (int i = 0; i < containing.Count; i++)
            {
                if (containing[i] != null)
                {
                    Gizmos.DrawSphere(containing[i].transform.position, 0.1f);
                    Gizmos.DrawLine(transform.position, containing[i].transform.position);
                }
            }
        }
    }
#endif
}