一. 泛型单例

public class Singleton<T> {
    private T _instance;
    private readonly object _locker = new object();
    public T Instance {
        get {
            if (_instance == null) {
                lock (_locker) {
                    if (_instance == null) {
                        Type t = typeof(T);
                        ConstructorInfo[] ctors = t.GetConstructors();//获得所有公共构造函数
                        if (ctors.Length > 0) {
                            throw new InvalidOperationException(String.Format("{0} has at least one accesible ctor", t.Name));
                        }
                        _instance = (T)Activator.CreateInstance(t, true);//true匹配所有无参构造，false仅匹配公有无参构造
                    }
                }
            }
            return _instance;
        }
    }
}

二. 继承Mono的泛型单例

1. 饿汉式

需在Scene中手动挂载到GameObject上

第一种

public class SingletonMono<T> : MonoBehaviour where T : MonoBehaviour {
    private static T _instance;
    public static T Instance {
        get {
            if (_instance == null) {
                if (Debug.isDebugBuild) {//开发版本Debug，发布版本不Debug，降低性能影响
                    Debug.LogError(typeof(T) + " has no instance");
                }
            }
            return _instance;
        }
    }

    private void Awake() {
        if (_instance != null) {
            if (Debug.isDebugBuild) {
                Debug.LogError(typeof(T) + " had has an instance");
            }
        }
        _instance = this as T;
        InitAwake();
    }

    protected virtual void InitAwake() { }//子类重写该方法当作Awake
}

使用

public class GameManager : SingletonMono<GameManager> {
    protected override void InitAwake() {
    	//DO STH
    }
}

第二种

public class SingletonMono<T> : MonoBehaviour where T : MonoBehaviour {
    private static T _instance;
    public static T Instance {
        get {
            if (_instance == null) {
                if (Debug.isDebugBuild) {
                    Debug.LogError(typeof(T) + " has no instance");
                }
            }
            return _instance;
        }
    }

    protected void Awake() {
        if (_instance != null) {
            if (Debug.isDebugBuild) {
                Debug.LogError(typeof(T) + " had has an instance");
            }
        }
        _instance = this as T;
    }
}

使用

public class GameManager : SingletonMono<GameManager> {
    public new void Awake() {
        base.Awake();
        //DO STH
    }
}

2. 懒汉式

使用时创建

public class SingletonMonoAuto<T> : MonoBehaviour where T : MonoBehaviour {
    private static T _instance;
    private static bool ApplicationIsQuitting;
    private static readonly object _locker = new object();
    static SingletonMonoAuto() { ApplicationIsQuitting = false; }

    void OnApplicationQuit() {
        ApplicationIsQuitting = true;
    }

    public static T Instance {
        get {
            if (ApplicationIsQuitting) {
                if (Debug.isDebugBuild) Debug.LogError("can't get instance");
            }
            if (_instance == null) {
                lock (_locker) {
                    if (_instance == null) {
                        _instance = FindObjectOfType<T>();
                        if (_instance == null) {
                            GameObject obj = new GameObject("SingltonMonoAuto_" + typeof(T));
                            _instance = obj.AddComponent<T>();
                        }
                    }
                }
            }
            return _instance;
        }
    }
}