结合Unity开发的设计模式之单例模式（Singleton Pattern）

1.1 模式概念：

• 创建型模式。
• 确保一个类只有一个实例，并且向整个系统提供这一个实例

1.2 模式结构：

• 单例 Singleton<T>，MonoSingleton<T>

1.3 代码示例：

public interface ISingleton
{
    void OnSingletonInit();
}

public abstract class Singleton<T> : ISingleton where T : Singleton<T>
{
    public abstract void OnSingletonInit();

    private static T instance;
    private static readonly object mLock = new object();

    public static T Instance
    {
        get
        {
            lock (mLock)
            {
                if (instance == null)
                {
                    instance = SingletonCreator.CreateSingleton<T>();
                }
            }

            return instance;
        }
    }


    public virtual void Dispose()
    {
        instance = null;
    }
}

public static class SingletonCreator
{
    public static T CreateSingleton<T>() where T : class, ISingleton
    {
        var ctors = typeof(T).GetConstructors(BindingFlags.Instance | BindingFlags.NonPublic);

        var ctor = Array.Find(ctors, p => p.GetParameters().Length == 0);

        if (ctor == null)
        {
            throw new Exception("Non-Public Constructors() not found! in " + typeof(T));
        }

        var instance = ctor.Invoke(null) as T;

        return instance;
    }
}

public static class SingletonProperty<T> where T : class, ISingleton
{
    private static T instance;
    static object mLock = new object();

    public static T Instance
    {
        get
        {
            lock (mLock)
            {
                if (instance == null)
                {
                    instance = SingletonCreator.CreateSingleton<T>();
                }
            }

            return instance;
        }
    }

    public static void Dispose()
    {
        instance = null;
    }
}

public abstract class MonoSingleton<T> : MonoBehaviour, ISingleton where T : MonoSingleton<T>
{
    public abstract void OnSingletonInit();

    private static T instance;

    public static T Instance
    {
        get
        {
            if (instance == null)
            {
                instance = MonoSingletonCreator.CreateMonoSigleton<T>();
            }

            return instance;
        }
    }
}

public static class MonoSingletonCreator
{
    public static T CreateMonoSigleton<T>() where T : MonoBehaviour, ISingleton
    {
        T instance = null;
        instance = UnityEngine.Object.FindObjectOfType(typeof(T)) as T;

        if (instance == null)
        {
            instance = new GameObject("_" + typeof(T)).AddComponent(typeof(T)) as T;
        }

        return instance;
    }
}

public static class MonoSingletonProperty<T> where T : MonoBehaviour, ISingleton
{
    private static T instance;

    public static T Instance
    {
        get
        {
            if (instance == null)
            {
                instance = MonoSingletonCreator.CreateMonoSigleton<T>();
            }

            return instance;
        }
    }
}

public class SingletonExample : MonoBehaviour
{
    void Start()
    {
        SingletonProperty<ShowSingletonMsg>.Instance.OnSingletonInit();
    }
}

public class ShowSingletonMsg : ISingleton
{
    private ShowSingletonMsg()
    {
    }

    public void OnSingletonInit()
    {
        UnityEngine.Debug.Log("初始化");
    }
}

public class MonoSingletonExample : MonoBehaviour
{
    void Start()
    {
        MonoSingletonProperty<ShowMonoSingleMsg>.Instance.OnSingletonInit();
    }
}

public class ShowMonoSingleMsg : MonoBehaviour, ISingleton
{
    public void OnSingletonInit()
    {
        Debug.Log("初始化");
    }
}

1.4 模式分析：

• 只有一个实例，减少内存开销，避免创建和销毁产生的大量垃圾。
• 全局只有一个实例，避免繁杂的引用。

1.5 应用场景：

• 全局访问

1.6 总结：

参考：