Unity useful scripts

MonoBehaviourSingleton.cs

#define SAMPLE_OUTSIDE_EDITOR

using UnityEngine;
using UnityEngine.Profiling;

public class MonoBehaviourSingleton<T> : MonoBehaviour where T : MonoBehaviourSingleton<T>
{
  static MonoBehaviourSingleton<T> instance;

  // Used to select the behavior of the singleton when it's destroyed, if it's "true" then
  // the instance value will be set to "null" when the MonoBehavior is Destroyed, otherwise 
  // it will keep the last instance value.
  // If it's false, then Instance will try to find a new non destroyed instance of the singleton in the scene, if
  // it can't find one, it will return the last value. Can be useful for components that need to access the singleton
  // after it has been destroyed to remove references / set some values / etc..
  protected static bool setToNullAfterDestroy = true;

  // Used to detect if the singleton is destroyed or not. We can't rely on the value of "instance" because
  // it's value will be kept if "setToNullAfterDestroy" is false.
  static bool destroyed = true;

  // Used to detect if the singleton was found at least once, and if it wasn't then show 
  // an error message informing this when trying to access the Instance
  static bool initializedAtLeastOnce = false;

  // Used to detect if the singleton's Initialize() function needs to be called
  static bool needInitialization = true;

  protected bool Destroyed
  {
    get { return destroyed; }
  }

  public void Awake()
  {
    if (instance == null || destroyed) 
    {
      instance = this;
      destroyed = false;
    } 
    else if(instance != this)
    {
      Debug.LogError("Two instances of the same singleton '" + this + "'");
    }

    if (needInitialization)
    {
      needInitialization = false;
      initializedAtLeastOnce = true;

      #if UNITY_EDITOR || SAMPLE_OUTSIDE_EDITOR
      Profiler.BeginSample(instance.name + ".Initialize");
      #endif

      Initialize ();

      #if UNITY_EDITOR || SAMPLE_OUTSIDE_EDITOR
      Profiler.EndSample();
      #endif
    }
  }

  public void OnDestroy()
  {
    #if UNITY_EDITOR || SAMPLE_OUTSIDE_EDITOR
    Profiler.BeginSample(name + ".Destroy");
    #endif

    Destroy();

    #if UNITY_EDITOR || SAMPLE_OUTSIDE_EDITOR
    Profiler.EndSample();
    #endif
    destroyed = true;
    needInitialization = true;

    if (setToNullAfterDestroy)
      instance = null;
  }

  public static T Instance
  {
    get 
    { 
      if (instance == null || destroyed || needInitialization)
      {
        if (instance == null || destroyed)
        {
          MonoBehaviourSingleton<T> newInstance = MonoBehaviour.FindObjectOfType<MonoBehaviourSingleton<T>>();

          if (newInstance != null)
          {
            instance = newInstance;
            destroyed = false;
          }
        }

        if (instance != null && !destroyed)
        {
          if (needInitialization)
          {
            needInitialization = false;
            initializedAtLeastOnce = true;
          }
        }
        else
        {
          if (!initializedAtLeastOnce)
            Debug.LogError("Missing Singleton '" + typeof(T).Name + "'");
        }
      }

      return (T) instance; 
    }
  }

  public static void Dispose()
  {
    if (instance != null && !destroyed)
    {
      Destroy(instance.gameObject);

      instance = null;
    }
  }

  protected virtual void Initialize()
  {
  }

  protected virtual void Destroy()
  {
  }

  static public bool IsInitialized()
  {
    return instance != null && !destroyed;
  }

  static public bool IsAvailable()
  {
    return (IsInitialized() || MonoBehaviour.FindObjectOfType<MonoBehaviourSingleton<T>>() != null);
  }
}