ObjectTracker.cs

using System.Collections.Generic;
using UnityEngine;

public class ObjectTracker
{
    private class TrackedObject
    {
        private object m_Obj;
        private bool m_Initialized = false;
        private List<System.Action<object>> m_References = new List<System.Action<object>>();
        public void AddReference(System.Action<object> aRef)
        {
            if (!m_Initialized)
                m_References.Add(aRef);
            else
                aRef(m_Obj);
        }
        public void Initialize(object aObj)
        {
            if (!m_Initialized)
            {
                m_Initialized = true;
                m_Obj = aObj;
                foreach(var r in m_References)
                {
                    r(m_Obj);
                }
                m_References = null;
            }
        }
    }

    // singleton
    private static ObjectTracker m_Inst;
    public static ObjectTracker Instance
    {
        get
        {
            if (m_Inst == null)
                m_Inst = new ObjectTracker();
            return m_Inst;
        }
    }

    private Dictionary<string, TrackedObject> m_Objs = new Dictionary<string, TrackedObject>();
    private TrackedObject GetTrackedObject(string aID)
    {
        TrackedObject to;
        if (!m_Objs.TryGetValue(aID, out to))
        {
            to = new TrackedObject();
            m_Objs.Add(aID, to);
        }
        return to;
    }

    public void AddObject(string aID, object aObj)
    {
        GetTrackedObject(aID).Initialize(aObj);
    }
    public void GetObject(string aID, System.Action<object> aRef)
    {
        GetTrackedObject(aID).AddReference(aRef);
    }
}