NopCommerce源码架构详解-单例模式实现源码分析

NopCommerce源码架构详解概述

概述

NopCommerce源码架构详解-单例模式实现源码分析。

内容

单例模式是23种常用设计模式中最简单的设计模式之一。.NET中单例模式的实现也有很多种方式。下面我来介绍一下NopCommerce中单例模式实现。

我之前的文章就分析了一下nop中EngineContext的实现。EngineContext是把一个Web请求用Nop的EngineContext引擎上下文封装。里面提供了一个IEngine的单例对象的访问方式。

下面就是EngineContext的源码：

1、EngineContext

using System;
using System.Configuration;
using System.Runtime.CompilerServices;
using Nop.Core.Configuration;

namespace Nop.Core.Infrastructure
{
    public class EngineContext
    {
        #region Utilities

        /// <summary>
        /// 通过配置信息创建一个相应IEngine实例
        /// </summary>
        /// <param name="config">Config</param>
        /// <returns>New engine instance</returns>
        protected static IEngine CreateEngineInstance(NopConfig config)
        {
            if (config != null && !string.IsNullOrEmpty(config.EngineType))
            {
                var engineType = Type.GetType(config.EngineType);
                if (engineType == null)
                    throw new ConfigurationErrorsException("The type '" + config.EngineType + "' could not be found. Please check the configuration at /configuration/nop/engine[@engineType] or check for missing assemblies.");
                if (!typeof(IEngine).IsAssignableFrom(engineType))
                    throw new ConfigurationErrorsException("The type '" + engineType + "' doesn't implement 'Nop.Core.Infrastructure.IEngine' and cannot be configured in /configuration/nop/engine[@engineType] for that purpose.");
                return Activator.CreateInstance(engineType) as IEngine;
            }

            return new NopEngine();
        }

        #endregion

        #region Methods

        /// <summary>
        /// Initializes a static instance of the Nop factory.初始化创建一个IEngine的实例
        /// </summary>
        /// <param name="forceRecreate">Creates a new factory instance even though the factory has been previously initialized.</param>
        [MethodImpl(MethodImplOptions.Synchronized)]
        public static IEngine Initialize(bool forceRecreate)
        {
            if (Singleton<IEngine>.Instance == null || forceRecreate)
            {
                var config = ConfigurationManager.GetSection("NopConfig") as NopConfig;
                Singleton<IEngine>.Instance = CreateEngineInstance(config);
                Singleton<IEngine>.Instance.Initialize(config);
            }
            return Singleton<IEngine>.Instance;
        }

        /// <summary>
        /// 替换单例中的实例对象
        /// </summary>
        /// <param name="engine">The engine to use.</param>
        /// <remarks>Only use this method if you know what you're doing.</remarks>
        public static void Replace(IEngine engine)
        {
            Singleton<IEngine>.Instance = engine;
        }

        #endregion

        /// <summary>
        /// 获取IEngine单例实例对象
        /// </summary>
        public static IEngine Current
        {
            get
            {
                if (Singleton<IEngine>.Instance == null)
                {
                    Initialize(false);
                }
                return Singleton<IEngine>.Instance;
            }
        }

    }
}

上面Initialize方法使用MethodImpl声明，就保证只能有一个线程访问，因为.NET的Web程序无论是WebForm还是mvc都在服务端都是多线程的。这样就标记只能有一个线程调用Initialize方法，也就保证了实例对象IEngine的在内存中只有一份。然后把单例实例对象的存储到类Singleton中。Singleton就像是一个对象容器，可以把许多单例实例对象存储在里面。

下面我们来看看实例Singleton的实现思路。

2、Singleton

ng System;
using System.Collections.Generic;

namespace Nop.Core.Infrastructure
{

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

        public static T Instance
        {
            get { return instance; }
            set
            {
                instance = value;
                AllSingletons[typeof(T)] = value;
            }
        }
    }

    public class SingletonList<T> : Singleton<IList<T>>
    {
        static SingletonList()
        {
            Singleton<IList<T>>.Instance = new List<T>();
        }

        public new static IList<T> Instance
        {
            get { return Singleton<IList<T>>.Instance; }
        }
    }

    public class SingletonDictionary<TKey, TValue> : Singleton<IDictionary<TKey, TValue>>
    {
        static SingletonDictionary()
        {
            Singleton<Dictionary<TKey, TValue>>.Instance = new Dictionary<TKey, TValue>();
        }

        public new static IDictionary<TKey, TValue> Instance
        {
            get { return Singleton<Dictionary<TKey, TValue>>.Instance; }
        }
    }

    public class Singleton
    {
        static Singleton()
        {
            allSingletons = new Dictionary<Type, object>();
        }

        static readonly IDictionary<Type, object> allSingletons;

        public static IDictionary<Type, object> AllSingletons
        {
            get { return allSingletons; }
        }
    }
}

Singleton类里面用一个Dictionary<Type, object>()集合来存储所有的单例对象。基于Singleton类创建一些泛型类Singleton，Singleton<IList>，SingletonList，Singleton<IDictionary<TKey, TValue>>和SingletonDictionary<TKey, TValue>。