增加A2WToolBox工具集，增加Launch场景核LaunchPanel

Assets/A2WToolBox/Runtime/Singleton/Singleton.cs

@@ -0,0 +1,51 @@
+using UnityEngine;
+
+namespace A2W
+{
+    public class Singleton<T> : MonoBehaviour where T : MonoBehaviour
+    {
+        private static T _instance;
+        private static object _lock = new object();
+        public static T instance
+        {
+            get
+            {
+                if (applicationIsQuitting)
+                {
+                    return null;
+                }
+                lock (_lock)
+                {
+                    if (_instance == null)
+                    {
+                        _instance = (T)FindObjectOfType(typeof(T));
+
+                        if (FindObjectsOfType(typeof(T)).Length > 1)
+                        {
+                            return _instance;
+                        }
+
+                        if (_instance == null)
+                        {
+                            GameObject singleton = new GameObject();
+                            _instance = singleton.AddComponent<T>();
+                            singleton.name = "(singleton)" + typeof(T).ToString();
+
+                            DontDestroyOnLoad(singleton);
+                        }
+                    }
+
+                    return _instance;
+                }
+            }
+        }
+
+        private static bool applicationIsQuitting = false;
+
+        public void OnDestroy()
+        {
+            applicationIsQuitting = true;
+        }
+    }
+}
+