GrabEvents.cs

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

public class GrabEvents : MonoBehaviour
{
    private OVRGrabbable grabbable;

    public UnityEvent StartGrab;
    public UnityEvent EndGrab;
    public UnityEvent WhileGrabbed;

    private bool _grabNotified;
    private bool _releaseNotified;


    void Start()
    {
        grabbable = gameObject.GetComponent<OVRGrabbable>();
    }

    void Update()
    {
        if (grabbable.isGrabbed)
        {
            WhileGrabbed.Invoke();
        }

        if (grabbable.isGrabbed && !_grabNotified)
        {
            StartGrab.Invoke();
            _grabNotified = true;
            _releaseNotified = false;
        }

        if (!grabbable.isGrabbed && !_releaseNotified)
        {
            EndGrab.Invoke();
            _grabNotified = false;
            _releaseNotified = true;
        }
    }
}