Pigeons.cs

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

public class Pigeons : MonoBehaviour
{
    public class PigeonEvent<T> : UnityEvent<T>{}

    /// <summary> If true, a GameObject has been created and marked as DontDestroyOnLoad, and this component has been attached. </summary>
    private static bool m_isInit = false;

    /// <summary> Singleton instance of the Pigeons class. Null if Pigeons hasn't been initialized yet. </summary>
    private static Pigeons m_instance;

    protected static Pigeons Instance
    {
        get
        {
            Init();
            return m_instance;
        }
    }

    private int m_subscriptionCount = 0;
    private bool m_applicationQuitting;
    private Hashtable m_subscriberCallbacks = new Hashtable();

    private void UpdateDisplayName()
    {
        gameObject.name = string.Format("Piegons (Subscribers: {0})", m_subscriptionCount);
    }

    private void OnApplicationQuit()
    {
        m_applicationQuitting = true;
    }

    private static void Init()
    {
        if (m_isInit)
            return;

        // Check to see that no one accidentally put one of these guys in the scene already.
        Pigeons[] existingPigeons = FindObjectsOfType<Pigeons>();
        if(existingPigeons.Length > 0)
        {
            Debug.LogError("[Pigeons.Messenger] Found existing Pigeons component in the scene. Please do not put one in the scene! Destroying scene copy.");
            foreach (Pigeons existing in existingPigeons)
                Destroy(existing);
        }

        GameObject gO = new GameObject("Pigeons (Subscribers: 0)");
        m_instance = gO.AddComponent<Pigeons>();
        m_isInit = true;
        DontDestroyOnLoad(gO);
        Debug.Log("[Pigeons.Messenger] An instance of Pigeons was needed in the scene, so it was automatically created.");
    }


    private void SubscribeInternal<T>(UnityAction<T> messageCallback)
    {
        if (m_applicationQuitting)
            return;

        if (!m_subscriberCallbacks.ContainsKey(typeof(T)))
            m_subscriberCallbacks[typeof(T)] = new PigeonEvent<T>();

        ((PigeonEvent<T>)m_subscriberCallbacks[typeof(T)]).AddListener(messageCallback);
        m_subscriptionCount++;
        UpdateDisplayName();
    }

    private void UnsubscribeInternal<T>(UnityAction<T> messageCallback)
    {
        if (m_applicationQuitting)
            return;

        if (!m_subscriberCallbacks.ContainsKey(typeof(T)))
        {
            Debug.LogWarning(string.Format("Pigeons.Messenger] Attempted to unsubscribe type {0} but no subscriptions found."));
            return;
        }

        ((PigeonEvent<T>)m_subscriberCallbacks[typeof(T)]).RemoveListener(messageCallback);
        m_subscriptionCount--;
        UpdateDisplayName();
    }

    private void SendInternal<T>(T message) 
    {
        if (m_applicationQuitting)
            return;

        ((PigeonEvent<T>)m_subscriberCallbacks[typeof(T)]).Invoke(message);
    }

    #region Public Static API

    public static void Subscribe<T>(UnityAction<T> messageCallback)
    {
        Instance.SubscribeInternal<T>(messageCallback);
    }

    public static void Unsubscribe<T>(UnityAction<T> messageCallback)
    {
        Instance.UnsubscribeInternal<T>(messageCallback);
    }

    public static void Send<T>(T message)
    {
        Instance.SendInternal<T>(message);
    }

    #endregion
}