SingleInstance.cs

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// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License. See LICENSE in the project root for license information.

using UnityEngine;

namespace HoloToolkit.Unity
{
    public class SingleInstance<T> : MonoBehaviour where T : SingleInstance<T>
    {
        private static T _Instance;
        public static T Instance
        {
            get
            {
                if (_Instance == null)
                {
                    T[] objects = FindObjectsOfType<T>();
                    if (objects.Length == 1)
                    {
                        _Instance = objects[0];
                    }
                    else if (objects.Length > 1)
                    {
                        Debug.LogErrorFormat("Expected exactly 1 {0} but found {1}", typeof(T).ToString(), objects.Length);
                    }
                }
                return _Instance;
            }
        }

        protected virtual void OnDestroy()
        {
            _Instance = null;
        }
    }
}