OnTrigger.cs

//Uses LayerMaskExtensions.cs https://pastebin.com/AZzRYSCJ

using UnityEngine;
using UnityEngine.Events;

public class OnTrigger : MonoBehaviour {

    public LayerMask triggerMask = -1;

    public TriggerEvent OnEnter;
    public TriggerEvent OnStay;
    public TriggerEvent OnExit;

    public void OnTriggerEnter(Collider hit) {

        if(triggerMask.LayerInMask(hit.gameObject.layer))
            if(OnEnter != null) OnEnter.Invoke(hit);
    }

    public void OnTriggerStay(Collider hit) {
        if(triggerMask.LayerInMask(hit.gameObject.layer))
            if(OnStay != null) OnStay.Invoke(hit);
    }

    public void OnTriggerExit(Collider hit) {
        if(triggerMask.LayerInMask(hit.gameObject.layer))
            if(OnExit != null) OnExit.Invoke(hit);
    }

    /// <summary>
    /// A UnityEvent with a Collider parameter.
    /// </summary>
    [System.Serializable]
    public class TriggerEvent : UnityEvent<Collider> { }
}