For Unity3D, converts Trigger methods into Delegates.

TriggerCallback.cs

using UnityEngine;
using System.Collections;

public class TriggerCallback : MonoBehaviour {
	public delegate void Enter(Collider other);
	public Enter enter;
	public delegate void Exit(Collider other);
	public Exit exit;
	public delegate void Stay(Collider other);
	public Stay stay;
	void Awake(){
		enter+=DoNothing;
		exit+=DoNothing;
		stay+=DoNothing;
	}
	void DoNothing(Collider other){}
	void OnTriggerEnter(Collider other){
		enter(other);
	}
	void OnTriggerExit(Collider other){
		exit(other);
	}
	void OnTriggerStay(Collider other){
		stay(other);
	}

}