NopCommerce源码架构详解--Autofac依赖注入分析

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));
}
转自蓝狐官网