ScriptableSingleton.cs

using UnityEngine;
#if UNITY_EDITOR
using UnityEditor;
using System.IO;
#endif
using System.Collections;

/** Utility class for handling singleton ScriptableObjects for data management */
public abstract class ScriptableSingleton<T> : ScriptableObject where T : ScriptableSingleton<T>{

	private static string FileName{
		get{
			return typeof(T).Name;
		}
	}

	#if UNITY_EDITOR
	private static string AssetPath{
		get{
			return "Assets/Resources/" + FileName + ".asset";
		}
	}
	#endif

	private static string ResourcePath{
		get{
			return FileName;
		}
	}

	public static T Instance{
		get{
			if(cachedInstance == null){
				cachedInstance = Resources.Load(ResourcePath) as T;
			}
			#if UNITY_EDITOR
			if(cachedInstance == null){
				cachedInstance = CreateAndSave();
			}
			#endif
			if(cachedInstance == null){
				Debug.LogWarning("No instance of " + FileName + " found, using default values");
				cachedInstance = ScriptableObject.CreateInstance<T>();
				cachedInstance.OnCreate();
			}

			return cachedInstance;
		}
	}	
	private static T cachedInstance;

	#if UNITY_EDITOR
	protected static T CreateAndSave(){
		T instance = ScriptableObject.CreateInstance<T>();
		instance.OnCreate();
		//Saving during Awake() will crash Unity, delay saving until next editor frame
		if(EditorApplication.isPlayingOrWillChangePlaymode){
			EditorApplication.delayCall += () => SaveAsset(instance);
		}
		else{
			SaveAsset(instance);
		}
		return instance;
	}

	private static void SaveAsset(T obj){
		string dirName = Path.GetDirectoryName(AssetPath);
		if(!Directory.Exists(dirName)){
			Directory.CreateDirectory(dirName);
		}
		AssetDatabase.CreateAsset(obj, AssetPath);
		AssetDatabase.SaveAssets();
		Debug.Log("Saved " + FileName + " instance");
	}
	#endif

	protected virtual void OnCreate(){
		// Do setup particular to your class here
	}
}