Add Singleton and MonoSingleton

Assets/Scripts/GameManager.cs

@@ -3,7 +3,7 @@
 using UnityEngine;
 using UnityEngine.SceneManagement;
 
-public class GameManager : Singleton<GameManager>
+public class GameManager : MonoSingleton<GameManager>
 {
 
 	[SerializeField]

Assets/Scripts/MonoSingleton.cs

@@ -0,0 +1,63 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+
+public abstract class MonoSingleton<T> : MonoBehaviour where T : Component
+{
+
+	#region Fields
+
+	/// <summary>
+	/// The instance.
+	/// </summary>
+	private static T instance;
+
+	#endregion
+
+	#region Properties
+
+	/// <summary>
+	/// Gets the instance.
+	/// </summary>
+	/// <value>The instance.</value>
+	public static T Instance
+	{
+		get
+		{
+			if ( instance == null )
+			{
+				instance = FindObjectOfType<T> ();
+				if ( instance == null )
+				{
+					GameObject obj = new GameObject ();
+					obj.name = typeof ( T ).Name;
+					instance = obj.AddComponent<T> ();
+				}
+			}
+			return instance;
+		}
+	}
+
+	#endregion
+
+	#region Methods
+
+	/// <summary>
+	/// Use this for initialization.
+	/// </summary>
+	protected virtual void Awake ()
+	{
+		if ( instance == null )
+		{
+			instance = this as T;
+			DontDestroyOnLoad ( gameObject );
+		}
+		else
+		{
+			Destroy ( gameObject );
+		}
+	}
+
+	#endregion
+
+}

Assets/Scripts/Singleton.cs

@@ -1,63 +1,82 @@
-using System.Collections;
+using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
-public abstract class Singleton<T> : MonoBehaviour where T : Component
+public abstract class Singleton<T> where T : Singleton<T>, new()
 {
-
-	#region Fields
-
-	/// <summary>
-	/// The instance.
-	/// </summary>
-	private static T instance;
-
-	#endregion
-
-	#region Properties
-
-	/// <summary>
-	/// Gets the instance.
-	/// </summary>
-	/// <value>The instance.</value>
-	public static T Instance
-	{
-		get
-		{
-			if ( instance == null )
-			{
-				instance = FindObjectOfType<T> ();
-				if ( instance == null )
-				{
-					GameObject obj = new GameObject ();
-					obj.name = typeof ( T ).Name;
-					instance = obj.AddComponent<T> ();
-				}
-			}
-			return instance;
-		}
-	}
-
-	#endregion
-
-	#region Methods
-
-	/// <summary>
-	/// Use this for initialization.
-	/// </summary>
-	protected virtual void Awake ()
-	{
-		if ( instance == null )
-		{
-			instance = this as T;
-			DontDestroyOnLoad ( gameObject );
-		}
-		else
-		{
-			Destroy ( gameObject );
-		}
-	}
-
-	#endregion
-
+
+    #region Fields
+
+    /// <summary>
+    /// The instance.
+    /// </summary>
+    private static T instance;
+
+    #endregion
+
+    #region Properties
+
+    /// <summary>
+    /// Gets the instance.
+    /// </summary>
+    /// <value>The instance.</value>
+    public static T Instance
+    {
+        get
+        {
+            if (Instance == null)
+            {
+                //ensure that only one thread can execute
+                lock (typeof(T))
+                {
+                    if (Instance == null)
+                    {
+                        instance = new T();
+                        instance.Init();
+                    }
+                }
+            }
+
+            return instance;
+        }
+    }
+
+
+    #endregion
+
+    #region Methods
+
+    public static void CreateInstance()
+    {
+        DestroyInstance();
+        instance = Instance;
+    }
+
+    public static void DestroyInstance()
+    {
+        if (instance == null) return;
+
+        instance.Clear();
+        instance = default(T);
+    }
+
+    protected void Init()
+    {
+        OnInit();
+    }
+
+    public void Clear()
+    {
+        OnClear();
+    }
+
+    protected virtual void OnInit()
+    {
+    }
+
+    protected virtual void OnClear()
+    {
+    }
+    #endregion
+
 }

ProjectSettings/ProjectVersion.txt

@@ -1 +1,2 @@
-m_EditorVersion: 2017.1.0p4
+m_EditorVersion: 2021.3.6f1c1
+m_EditorVersionWithRevision: 2021.3.6f1c1 (07401303b748)