Trigger activator/handler for Unity3D

Trigger3D.cs

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

/// <summary>
/// Trigger3D class
/// 
/// A trigger is considered ACTIVE when there is at least one object inside of it.
/// 
/// Contains a list of objects inside the trigger, and if the trigger is active or not.
/// The user is responsible for setting up proper layering for collisions with this object.
/// </summary>
[AddComponentMenu("Event/Event Trigger3D")]
[RequireComponent( typeof(Collider) )]
public class Trigger3D : MonoBehaviour
{
	///This trigger is considered active when another object is inside of it.  It is inactive if no objects are inside of it
	public bool Active { get { return inside.Count > 0; } }

	private Collider col3D;
	/// The 3D Collider for this trigger.
	public Collider ColliderComponent { get { return col3D ?? (col3D = GetComponent<Collider>()); } }

	///all the objects inside this trigger
	List<Collider> inside = new List<Collider>();

	///A list of all the 3d colliders currently inside the 3d trigger
	public IEnumerable<Collider> Inside { get { return inside; } }

	[SerializeField, Tooltip("called when this trigger is activated by a 3d collider")]
	UnityEvent onActivate;
	public UnityEvent OnActivate { get { return onActivate; } }

	[SerializeField, Tooltip("called when this trigger is deactivated by a 3d collider")]
	UnityEvent onDeactivate;
	public UnityEvent OnDeactivate { get { return onDeactivate; } }

	[Serializable]
	public class ColliderEvent : UnityEvent<Collider> { }
	
	[SerializeField, Tooltip("called when a 3d collider enters this trigger")]
	ColliderEvent onEnter;
	public ColliderEvent OnEnter { get { return onEnter; } }
	
	[SerializeField, Tooltip("called when a 3d collider exists this trigger")]
	private ColliderEvent onExit;
	public ColliderEvent OnExit { get { return onExit; } }

	void Awake()
	{
		ColliderComponent.isTrigger = true;
	}

	void OnTriggerEnter(Collider other)
	{
		bool wasActive = Active;

		inside.Add(other);
		OnEnter.Invoke(other);

		if (!wasActive)
			OnActivate.Invoke();
	}

	void OnTriggerExit(Collider other)
	{
		bool wasActive = Active;

		inside.Remove(other);

		OnExit.Invoke(other);

		if (wasActive && !Active)
			OnDeactivate.Invoke();
	}
}