using UnityEngine;
using System.Collections;

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

    /**
       Returns the instance of this singleton.
    */
    public static T Instance
    {
        get
        {
            if(instance == null)
            {
                instance = (T)FindObjectOfType(typeof(T));

                if(instance == null)
                {
                    //Try finding non-active scene object
                    var objects = Resources.FindObjectsOfTypeAll<T>();
                    if(objects.Length > 0)
                        instance = objects[0];
                }
                if(instance == null)
                {
                    Debug.LogError("An instance of " + typeof(T) +
                       " is needed in the scene, but there is none.");

                }
            }

            return instance;
        }
    }
}

// Example

public class GameManager : Singleton<GameManager>
{
    public int value = 1;
}

// you can access value from anywhere with this
GameManager.instance.value;