NopCommerce中的單例

項目中經常會遇到單例的情況。大部分的單例代碼都差不多像這樣定義:

internal class SingletonOne
    {
        private static SingletonOne _singleton;

        private SingletonOne()
        {
        }

        public static SingletonOne Instance
        {
            get
            {
                if (_singleton == null)
                {
                    var instance = new SingletonOne();
                    Interlocked.CompareExchange(ref _singleton, instance, null);
                }

                return _singleton;
            }
        }
    }

但是很明顯的一個缺點是這個類只能用作單例。

最近看了NopCommerce對單例有個包裝。覺得有點新穎 給大家分享一下。

/// <summary>
    /// Provides access to all "singletons" stored by <see cref="Singleton{T}"/>.
    /// </summary>
    public class Singleton
    {
        static Singleton()
        {
            allSingletons = new Dictionary<Type, object>();
        }

        static readonly IDictionary<Type, object> allSingletons;

        /// <summary>Dictionary of type to singleton instances.</summary>
        public static IDictionary<Type, object> AllSingletons
        {
            get { return allSingletons; }
        }
    }

public class Singleton<T> : Singleton
    {
        static T instance;

        /// <summary>The singleton instance for the specified type T. Only one instance (at the time) of this object for each type of T.</summary>
        public static T Instance
        {
            get { return instance; }
            set
            {
                instance = value;
                AllSingletons[typeof(T)] = value;
            }
        }
    }

比如定義了一個類, 那麼可以這樣使用

public class Fake
{
}

Singleton<Fake>.Instance = new Fake();