Useful Unity Scripts

Singleton.cs

using UnityEditor;
using UnityEngine;

namespace UnityTemplateProjects.Misc
{
    /// <summary>
    /// Inherit from this base class to create a singleton.
    /// e.g. public class MyClassName : Singleton<MyClassName> {}
    /// </summary>
    public class Singleton<T> : MonoBehaviour where T : MonoBehaviour
    {
        // Check to see if we're about to be destroyed.
        private static bool m_ShuttingDown = false;
        private static object m_Lock = new object();
        private static T m_Instance;
 
        /// <summary>
        /// Access singleton instance through this propriety.
        /// </summary>
        public static T Instance
        {
            get
            {
                if (m_ShuttingDown && !Application.isEditor)
                {
                    Debug.LogWarning("[Singleton] Instance '" + typeof(T) +
                                     "' already destroyed. Returning null.");
                    return null;
                }
                lock (m_Lock)
                {
                    if (m_Instance == null)
                    {
                        // Search for existing instance.
                        m_Instance = FindObjectOfType(typeof(T)) as T;

                        if (m_Instance == null)
                        {
                            var o = GameObject.Find(typeof(T).ToString() + " (Singleton)");
                            if (o)
                            {
                                // Find by name
                                m_Instance = o.GetComponent<T>();
                                // Re-init as this gets lost on code recompile/reload.
                                (m_Instance as Singleton<T>).Init();
                            }
                        }

                        // Create new instance if one doesn't already exist.
                        if (m_Instance == null)
                        {
                            // Need to create a new GameObject to attach the singleton to.
                            var singletonObject = new GameObject();
                            singletonObject.hideFlags = HideFlags.DontSave;
                            m_Instance = singletonObject.AddComponent<T>();
                            singletonObject.name = typeof(T).ToString() + " (Singleton)";
                            (m_Instance as Singleton<T>).Init();

                            if (!Application.isEditor)
                            {
                                // Make instance persistent.
                                DontDestroyOnLoad(singletonObject);
                            }
                        }
                    }
 
                    return m_Instance;
                }
            }
        }

        protected virtual void Start()
        {
            //Debug.Log("Singleton Start called");
        }

        protected virtual void Init()
        {
            
        }

        // Start is called before the first frame update
        protected virtual void Awake()
        {
            if(m_Instance != null && m_Instance != gameObject as T)
            {
                Debug.LogError("[Singleton] Trying to create a second instance of singleton ", this);
                Destroy(gameObject);
            }
            else if (m_Instance == null)
            {
                m_Instance = this as T;
            }
        }
        
        private void OnApplicationQuit()
        {
            m_ShuttingDown = true;
        }
 
 
        private void OnDestroy()
        {
            m_ShuttingDown = true;
        }
    }
}