旧シングルトンの改良版。初回起動時にインスタンスが登録されていなければ自身を登録する

SingletonMonoBehaviour.cs

using UnityEngine;
using System.Collections;

public class SingletonMonoBehaviour<T> : MonoBehaviour where T : SingletonMonoBehaviour<T>
{
	protected static T instance;
	public static T Instance {
		get {
			if (instance == null) {
				instance = (T)FindObjectOfType (typeof(T));
				
				if (instance == null) {
					Debug.LogWarning (typeof(T) + "is nothing");
				}
			}
			
			return instance;
		}
	}
	
	protected void Awake()
	{
		CheckInstance();
	}
	
	protected bool CheckInstance()
	{
		if (instance == null)
		{
			instance = (T)this;
			return true;
		} else if (Instance == this)
		{
			return true;
		}

		Destroy(this);
		return false;
	}
}