Detect a OnClick Event in 3D Space on a GameObject

ClickDetector.cs

/*
 * Detects clicks on game objects
 * 
 * 1. Attach ClickDetector component to a camera or a "game manager" object
 * 2. Attach a collider (e.g. BoxCollider) to all objects that should receive a on click event
 * 3. Attach a MonoBehaviour to all objects that should receive a on click event registering to the event.
 * 
 * The MonoBehavior should have at least:
 * 
 * public class ClickableGameObject : MonoBehaviour, ClickDetector.ClickDetectorListener
 * {
 *     // Use this for initialization
 *     void Start()
 *     {
 *         Camera.main.GetComponent<ClickDetector>().AddListener(this);
 *     }
 *
 *     // Update is called once per frame
 *     void Update()
 *     {
 *     }
 *
 *     void OnDestroy()
 *     {
 *         Camera.main.GetComponent<ClickDetector>().RemoveListener(this);
 *     }
 *
 *     public void OnClick(RaycastHit hitInfo)
 *     {
 *         //do something
 *     }
 * }
 * 
 **/
using UnityEngine;
using System.Collections.Generic;

public class ClickDetector : MonoBehaviour
{
    /// <summary>
    /// Listeners
    /// </summary>
    protected Dictionary<GameObject, ClickDetectorListener> listeners = new Dictionary<GameObject, ClickDetectorListener>();

    /// <summary>
    /// Camera the component is attached to 
    /// </summary>
    protected Camera AttachedCamera;

    /// <summary>
    /// Check if connected to camera (not nessasaray)
    /// </summary>
    void Start()
    {
        AttachedCamera = GetComponent<Camera>();
    }

    /// <summary>
    /// Check collisions
    /// </summary>
    void Update()
    {
        var ray = ((AttachedCamera!=null)?AttachedCamera:Camera.main).ScreenPointToRay(Input.mousePosition);
        RaycastHit hit;
        if (Physics.Raycast(ray, out hit))
        {
            if (listeners.ContainsKey(hit.collider.gameObject) && Input.GetMouseButtonDown(0))
                listeners[hit.collider.gameObject].OnClick(hit);
        }
    }

    /// <summary>
    /// Add a listener
    /// </summary>
    /// <param name="listener"></param>
    public void AddListener(ClickDetectorListener listener)
    {
        listeners.Add(((Component)listener).gameObject, listener);
    }

    /// <summary>
    /// Remove a listener
    /// </summary>
    /// <param name="listener"></param>
    public void RemoveListener(ClickDetectorListener listener)
    {
        listeners.Add(((Component)listener).gameObject, listener);
    }

    /// <summary>
    /// Receiver for the on click event
    /// </summary>
    public interface ClickDetectorListener
    {
        /// <summary>
        /// the game object was clicked
        /// </summary>
        /// <param name="hitInfo">Additional Info of the raycast from the camera to the object</param>
        void OnClick(RaycastHit hitInfo);
    }
}