NopCommerce源码架构详解-Autofac依赖注入分析

NopCommerce源码架构详解概述

概述

NopCommerce源码架构详解-Autofac依赖注入分析。

内容

NopCommerce 整个代码里面都贯彻了一个面向接口编程的思想。nopCommerce商城系统是通过Autofac对接口依赖的实现进行依赖注入的。今天我们就来分析一下里面的源码，学习一下Nop在依赖注入方面设计思想，希望在以后的架构设计中对你有启发和帮助。

下面是Nop依赖注入相关类图。

可以看到这里面相关的类为

mvcApplication

IEngine，NopEngine

EngineContext

IDependencyRegistrar，DependencyRegistrar

下面我们再来看看这些类的核心代码。

我们打开Nop.Web项目的所有的Controller源码，可以看到基本上都是通过构造函数引用抽象的接口。如CustomerController的构造函数的参数类型都是某一个接口，如下图：

那我们要想看这些接口到底依赖的是哪一个真正的实现类呢？

在项目Nop.Web.Framework中有一个类DependencyRegistrar，其作用就是调用Autofac相关的API进行依赖注入，我们只要打开这个类文件，搜索一个指定的接口，就可以找到它依赖的具体类。例如，我们想看到ICategoryService接口是依赖哪一个实现，在这个类中搜索ICategoryService，会找到下面的代码：

builder.RegisterType<CategoryService>().As<ICategoryService>().InstancePerLifetimeScope();

可以看到这个接口对应的实现为CategoryService（Nop.Services.Catalog命名空间下的类CategoryService）。

下面我们来看看Nop在网站启动是怎么调用这个DependencyRegistrar类呢？

在项目Nop.Web也就是前台的起始项目有一个文件Global.asax里有一个函数Application_Start，这函数的意义这里就不用说了，我相信学过ASP.NET同学都知道它的作用，下面是函数Application_Start的完整代码：

protected void Application_Start()
{
    //初始化上下文引擎
    EngineContext.Initialize(false);

    //model binders
    ModelBinders.Binders.Add(typeof(BaseNopModel), new NopModelBinder());

    bool databaseInstalled = DataSettingsHelper.DatabaseIsInstalled();
    if (databaseInstalled)
    {
        //remove all view engines
        ViewEngines.Engines.Clear();
        //except the themeable razor view engine we use
        ViewEngines.Engines.Add(new ThemeableRazorViewEngine());
    }

    //Add some functionality on top of the default ModelMetadataProvider
    ModelMetadataProviders.Current = new NopMetadataProvider();

    //Registering some regular mvc stuff
    AreaRegistration.RegisterAllAreas();
    RegisterRoutes(RouteTable.Routes);

    //fluent validation
    DataAnnotationsModelValidatorProvider.AddImplicitRequiredAttributeForValueTypes = false;
    ModelValidatorProviders.Providers.Add(new FluentValidationModelValidatorProvider(new NopValidatorFactory()));

    //start scheduled tasks
    if (databaseInstalled)
    {
        TaskManager.Instance.Initialize();
        TaskManager.Instance.Start();
    }

    //log application start
    if (databaseInstalled)
    {
        try
        {
            //log
            var logger = EngineContext.Current.Resolve<ILogger>();
            logger.Information("Application started", null, null);
        }
        catch (Exception)
        {
            //don't throw new exception if occurs
        }
    }
}

里面有第一行代码就调用了上下文引擎初始化。

EngineContext.Initialize(false);

下面我们来看看这个EngineContext的静态方法Initialize：

[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;
}

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();
}

从上面可以看到Initialize返回一个IEngine的实例，并调用其方法Initialize。创建IEngine的实例是根据配置文件来获取哪一个IEngine的具体类，如果没有配置这个结点信息或者为空，则返回默认的IEngine的实现NopEngine。

下面我们来看看Nop.Core.Infrastructure.NopEngine里面的核心代码：

public void Initialize(NopConfig config)
{
     //注册依赖
     RegisterDependencies(config);

     //startup tasks
     if (!config.IgnoreStartupTasks)
     {
          RunStartupTasks();
     }

}

/// <summary>
/// 注册依赖
/// </summary>
/// <param name="config">Config</param>
protected virtual void RegisterDependencies(NopConfig config)
{
     var builder = new ContainerBuilder();
     var container = builder.Build();

     //we create new instance of ContainerBuilder
     //because Build() or Update() method can only be called once on a ContainerBuilder.

     //dependencies
     var typeFinder = new WebAppTypeFinder(config);
     builder = new ContainerBuilder();
     builder.RegisterInstance(config).As<NopConfig>().SingleInstance();
     builder.RegisterInstance(this).As<IEngine>().SingleInstance();
     builder.RegisterInstance(typeFinder).As<ITypeFinder>().SingleInstance();
     builder.Update(container);

     //register dependencies provided by other assemblies
     builder = new ContainerBuilder();
     //查找所有实现了接口IDependencyRegistrar的类
     var drTypes = typeFinder.FindClassesOfType<IDependencyRegistrar>();
     var drInstances = new List<IDependencyRegistrar>();
     foreach (var drType in drTypes)
          drInstances.Add((IDependencyRegistrar) Activator.CreateInstance(drType));
     //排序
     drInstances = drInstances.AsQueryable().OrderBy(t => t.Order).ToList();

     //依次调用实现IDependencyRegistrar接口的类的方法Register
     foreach (var dependencyRegistrar in drInstances)
          dependencyRegistrar.Register(builder, typeFinder);
     builder.Update(container);

     this._containerManager = new ContainerManager(container);

     //set dependency resolver
     DependencyResolver.SetResolver(new AutofacDependencyResolver(container));
}