lanlib/Scripts/Runtime/Singleton/Singleton.cs

using System.Linq;
using System.Reflection;
using UnityEngine;
using UnityEngine.Assertions;
using UnityEngine.SceneManagement;

namespace LanLib.Singleton
{
    [ExecuteInEditMode]
    public class Singleton<T> : SingletonBase where T : Singleton<T>
    {
        private const BindingFlags BindingFlags = System.Reflection.BindingFlags.Default
                                                  | System.Reflection.BindingFlags.FlattenHierarchy
                                                  | System.Reflection.BindingFlags.Static
                                                  | System.Reflection.BindingFlags.Public
                                                  | System.Reflection.BindingFlags.NonPublic;

        private static T _instance;

        public static T Instance
        {
            get
            {
                if (!_instance)
                {
#if UNITY_EDITOR
                    _instance = Resources.FindObjectsOfTypeAll<T>().FirstOrDefault(inst => inst);
#else
                    _instance = FindObjectOfType<T>();
#endif
                }

                if (!_instance)
                {
                    _instance = (T)typeof(T).GetMethod("CreateInstance", BindingFlags)?.Invoke(null, null);
                }

                Assert.IsNotNull(_instance);
                return _instance;
            }
        }

        protected static T CreateInstance()
        {
            return new GameObject(typeof(T).Name)
            {
                hideFlags = HideFlags.HideAndDontSave ^ HideFlags.NotEditable
            }.AddComponent<T>();
        }

        protected virtual void Awake()
        {
            if (_instance == null)
            {
                _instance = this as T;
                if (Application.isPlaying)
                {
                    DestroyOnSceneUnload = DestroyOnSceneUnload;
                }
            }
            else
            {
                DestroySelf();
            }
        }
    }

    public abstract class SingletonBase : MonoBehaviour
    {
        private SingletonDestroyCondition _destroyCondition = SingletonDestroyCondition.ReloadDomain;

        public virtual SingletonDestroyCondition DestroyCondition
        {
            get => _destroyCondition;
            private set
            {
                var flgSceneUnload = (value ^ _destroyCondition) & SingletonDestroyCondition.SceneUnload;
                if (flgSceneUnload != 0)
                {
                    var hasFlag = 0 != (value & SingletonDestroyCondition.SceneUnload);
                    DestroyOnSceneUnload = hasFlag;
                }

                _destroyCondition = value;
            }
        }

        public bool DestroyOnSceneUnload
        {
            get => DestroyCondition.Contains(SingletonDestroyCondition.SceneUnload);
            set
            {
                if (value)
                {
                    SceneManager.MoveGameObjectToScene(gameObject, SceneManager.GetActiveScene());
                    DestroyCondition |= SingletonDestroyCondition.SceneUnload;
                }
                else
                {
                    DontDestroyOnLoad(gameObject);
                    DestroyCondition &= ~SingletonDestroyCondition.SceneUnload;
                }
            }
        }

        internal void DestroySelf()
        {
            if (Application.isPlaying)
            {
                Destroy(gameObject);
            }
            else
            {
                DestroyImmediate(gameObject);
            }
        }
    }
}