【NopCommerce源碼架構學習-二】單例模式實現代碼分析，nopcommerce源碼

【NopCommerce源碼架構學習-二】單例模式實現代碼分析，nopcommerce源碼

單例模式是是常用經典十幾種設計模式中最簡單的。.NET中單例模式的實現也有很多種方式。下面我來介紹一下NopCommerce中單例模式實現。

我之前的文章就分析了一下nop中EngineContext的實現。EngineContext是把一個Web請求用Nop的EngineContext引擎上下文封裝。裡面提供了一個IEngine的單例對象的訪問方式。

下面就是EngineContext的源碼：

一、EngineContext

  1 using System.Configuration;
  2 
  3 using System.Runtime.CompilerServices;
  4 
  5 using Nop.Core.Configuration;
  6 
  7  
  8 
  9 namespace Nop.Core.Infrastructure
 10 
 11 {
 12 
 13     /// <summary>
 14 
 15     ///Provides access to the singleton instance of the Nop engine.
 16 
 17     ///提供了訪問單例實例Nop引擎
 18 
 19     /// </summary>
 20 
 21     public class EngineContext
 22 
 23     {
 24 
 25         #region Methods
 26 
 27  
 28 
 29         /// <summary>
 30 
 31         /// Initializes a static instance of the Nop factory.
 32 
 33         /// 初始化靜態Nop工廠的實例
 34 
 35         /// </summary>
 36 
 37         /// <param name="forceRecreate">創建一個新工廠實例,盡管工廠已經被初始化</param>
 38 
 39         [MethodImpl(MethodImplOptions.Synchronized)]
 40 
 41         public static IEngine Initialize(bool forceRecreate)
 42 
 43         {
 44 
 45             if (Singleton<IEngine>.Instance == null || forceRecreate)
 46 
 47             {
 48 
 49                 Singleton<IEngine>.Instance = new NopEngine();
 50 
 51  
 52 
 53                 var config = ConfigurationManager.GetSection("NopConfig") as NopConfig;
 54 
 55                 Singleton<IEngine>.Instance.Initialize(config);
 56 
 57             }
 58 
 59             return Singleton<IEngine>.Instance;
 60 
 61         }
 62 
 63  
 64 
 65         /// <summary>
 66 
 67         /// Sets the static engine instance to the supplied engine. Use this method to supply your own engine implementation.
 68 
 69         /// 設置靜態引擎實例提供的引擎,
 70 
 71         /// </summary>
 72 
 73         /// <param name="engine">The engine to use.</param>
 74 
 75         /// <remarks>Only use this method if you know what you're doing.</remarks>
 76 
 77         public static void Replace(IEngine engine)
 78 
 79         {
 80 
 81             Singleton<IEngine>.Instance = engine;
 82 
 83         }
 84 
 85        
 86 
 87         #endregion
 88 
 89  
 90 
 91         #region Properties
 92 
 93  
 94 
 95         /// <summary>
 96 
 97         /// Gets the singleton Nop engine used to access Nop services.
 98 
 99         /// </summary>
100 
101         public static IEngine Current
102 
103         {
104 
105             get
106 
107             {
108 
109                 if (Singleton<IEngine>.Instance == null)
110 
111                 {
112 
113                     Initialize(false);
114 
115                 }
116 
117                 return Singleton<IEngine>.Instance;
118 
119             }
120 
121         }
122 
123  
124 
125         #endregion
126 
127     }
128 
129 }

上面Initialize方法使用[MethodImpl(MethodImplOptions.Synchronized)]聲明，就保證只能有一個線程訪問，因為.NET的Web程序無論是WebForm還是mvc都在服務端都是多線程的。這樣就標記只能有一個線程調用Initialize方法，也就保證了實例對象IEngine的在內存中只有一份。然後把單例實例對象的存儲到類Singleton中。Singleton就像是一個對象容器，可以把許多單例實例對象存儲在裡面。

下面我們來看看實例Singleton的實現思路。

二、Singleton