阅读nopcommerce startup源码

创建一个asp.net core项目，可以到到startup类有两个方法

 // This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)

ConfigureServices方法：注册服务到容器中，在整个应用中都可以使用。推荐：自定义方法以Add开头 Configure方法：为应用配置请求管道.推荐：自定义方法以Use开头

这里并会深入的探讨依赖注入和IApplicationBuilder、IServiceCollection这些核心对象，这篇文章主要目的是快速的了解startup类和如何利用一些开源的项目（nopcommerce）去使用它。

nopcommerce是个优秀的开源的电商项目，应该都不会陌生，不管有没有项目中用到，但不妨碍我们去阅读学习他们优秀的地方。

一起先了解下项目结构 

• Nop.Core 核心层 ：包含领域模型、和基础设施层（缓存、仓储接口、依赖注入、对象映射mapper等）、一些其他工具里的封装
• Nop.Data 数据层：orm与数据库的一些操作，仓储实现类，领域和表的映射等
• Nop.Services 应用服务层：业务服务操作
• Plugins 插件：nop 是插件式开发 ，扩展起来很是方便
• Nop.Web 表现层：ui交互
• Nop.Web.Framework：对asp.netcore mvc 进行一些扩展和封装

在回到今天的主角startup类 我进入Nop.Web项目 打开startup类

 public class Startup
    {
        #region Fields

        private readonly IConfiguration _configuration;
        private readonly IHostingEnvironment _hostingEnvironment;

        #endregion

        #region Ctor

        public Startup(IConfiguration configuration, IHostingEnvironment hostingEnvironment)
        {
            _configuration = configuration;
            _hostingEnvironment = hostingEnvironment;
        }

        #endregion

        /// <summary>
        /// Add services to the application and configure service provider
        /// </summary>
        /// <param name="services">Collection of service descriptors</param>
        public IServiceProvider ConfigureServices(IServiceCollection services)
        {
            return services.ConfigureApplicationServices(_configuration, _hostingEnvironment);
        }

        /// <summary>
        /// Configure the application HTTP request pipeline
        /// </summary>
        /// <param name="application">Builder for configuring an application's request pipeline</param>
        public void Configure(IApplicationBuilder application)
        {
            application.ConfigureRequestPipeline();
        }
    }

是不是很简洁，可以发现nop对IServiceCollection、IApplicationBuilder进行扩展了两个方法类 分别ServiceCollectionExtensions、ApplicationBuilderExtensions，下面我们分别快速的浏览这两个类的源码

我们F12进入ConfigureApplicationServices的实现方式一步一步的查看

 var engine = EngineContext.Create();  //创建NopEngine
 var serviceProvider = engine.ConfigureServices(services, configuration);

  //find startup configurations provided by other assemblies
            var typeFinder = new WebAppTypeFinder();  //反射工具类
            var startupConfigurations = typeFinder.FindClassesOfType<INopStartup>();

            //create and sort instances of startup configurations
            var instances = startupConfigurations
                .Select(startup => (INopStartup)Activator.CreateInstance(startup))
                .OrderBy(startup => startup.Order);

            ////configure services
            foreach (var instance in instances)
                instance.ConfigureServices(services, configuration);

            ////register mapper configurations
            //AddAutoMapper(services, typeFinder);

            //register dependencies
            RegisterDependencies(services, typeFinder);

protected virtual IServiceProvider RegisterDependencies(IServiceCollection services, ITypeFinder typeFinder)
        {
            var containerBuilder = new ContainerBuilder(); //Autofac 

            //register engine
            containerBuilder.RegisterInstance(this).As<IEngine>().SingleInstance();

            //register type finder
            containerBuilder.RegisterInstance(typeFinder).As<ITypeFinder>().SingleInstance();

            //populate Autofac container builder with the set of registered service descriptors
            containerBuilder.Populate(services);

            //find dependency registrars provided by other assemblies
            var dependencyRegistrars = typeFinder.FindClassesOfType<IDependencyRegistrar>();

            //create and sort instances of dependency registrars
            var instances = dependencyRegistrars
                .Select(dependencyRegistrar => (IDependencyRegistrar)Activator.CreateInstance(dependencyRegistrar))
                .OrderBy(dependencyRegistrar => dependencyRegistrar.Order);

            //register all provided dependencies
            foreach (var dependencyRegistrar in instances)
                dependencyRegistrar.Register(containerBuilder, typeFinder);

            //create service provider
            _serviceProvider = new AutofacServiceProvider(containerBuilder.Build());

            return _serviceProvider;
        }

F12进入ConfigureRequestPipeline

  EngineContext.Current.ConfigureRequestPipeline(application);

 public void ConfigureRequestPipeline(IApplicationBuilder application)
        {
            //find startup configurations provided by other assemblies
            var typeFinder = Resolve<ITypeFinder>();
            var startupConfigurations = typeFinder.FindClassesOfType<INopStartup>();

            //create and sort instances of startup configurations
            var instances = startupConfigurations
                .Select(startup => (INopStartup)Activator.CreateInstance(startup))
                .OrderBy(startup => startup.Order);

            //configure request pipeline
            foreach (var instance in instances)
                instance.Configure(application);
        }

到此这两个文件的源码已经过完了，觉得很核心的几个对象

• EngineContext： NopEngine的实例上下文 作用 获取创建和获取NopEngine的实例上下文的实例（涉及到的设计模式单例）
• IEngine、NopEngine： nop引擎还是很体贴的，里面封装了使用的方法如ioc 解析方法Resolve
• INopStartup ：在应用程序启动时配置服务和中间件 当时我看过源码，有几处还是很巧妙的，下面我整理下，多个为什么，带着问题去看，印象更深刻，也达到了参考nop源码学习startup类的目的。

1. 接口INopStartup作用？ INopStartup有两个方法ConfigureServices，Configure 跟Startup方法作用都是一样的，nop把它抽离成接口的好处，可以很方便通过反射把实现INopStartup的类查找出来，然后掉用ConfigureServices，Configure方法

 //find startup configurations provided by other assemblies
            var typeFinder = new WebAppTypeFinder();
            var startupConfigurations = typeFinder.FindClassesOfType<INopStartup>();

            //create and sort instances of startup configurations
            var instances = startupConfigurations
                .Select(startup => (INopStartup)Activator.CreateInstance(startup))
                .OrderBy(startup => startup.Order);

            ////configure services
            foreach (var instance in instances)
                instance.ConfigureServices(services, configuration);
                
              //configure request pipeline
            foreach (var instance in instances)
                instance.Configure(application);    

2. nop使用Autofac作为注入框架，它是如何实现的

     var containerBuilder = new ContainerBuilder();
    //register engine
    containerBuilder.RegisterInstance(this).As<IEngine>().SingleInstance();
        
    //create service provider
    _serviceProvider = new AutofacServiceProvider(containerBuilder.Build());

     return _serviceProvider;

3. 接口IEngine的作用？ 配置startup 服务和请求管道、autofac注册和解析

IServiceProvider ConfigureServices(IServiceCollection services, IConfiguration configuration);
void ConfigureRequestPipeline(IApplicationBuilder application);
T Resolve<T>() where T : class;

4. 如何使用注入的服务？

1.我们在Nop.Services项目中添加ProductService和ProductAttributeService两个业务服务

    public class ProductService : IProductService
    {
        public string GetProductById(int productId)
        {
            return "获取产品";
        }
    }
    
  public class ProductAttributeService: IProductAttributeService
    {
        public  string GetProductAttributeById(int productAttributeId)
        {
            return "获取产品属性";
        }
    }
    

2.我们实现IDependencyRegistrar依赖注册接口

 public class DependencyRegistrar : IDependencyRegistrar
    {
        /// <summary>
        /// Register services and interfaces
        /// </summary>
        /// <param name="builder">Container builder</param>
        /// <param name="typeFinder">Type finder</param>
        public virtual void Register(ContainerBuilder builder, ITypeFinder typeFinder)
        {
            //file provider
            builder.RegisterType<NopFileProvider>().As<INopFileProvider>().InstancePerLifetimeScope();
            //data layer
            //repositories
            //services
            builder.RegisterType<ProductAttributeService>().As<IProductAttributeService>().InstancePerLifetimeScope();
            builder.RegisterType<ProductService>().As<IProductService>().InstancePerLifetimeScope();
        }

        /// <summary>
        /// Gets order of this dependency registrar implementation
        /// </summary>
        public int Order => 0;
    }

3.然后在homecontroller中测试，第一种构造函数注入，第二种直接使用IEngine的实例解析

       #region fileds
        private readonly IProductService productService;
        #endregion
        public HomeController(IProductService productService)
        {
            this.productService = productService;
        }
        public IActionResult Index()
        {
            //利用EngineContex进行解析
            var productAttributeService = EngineContext.Current.Resolve<IProductAttributeService>();
            ViewBag.result =  this.productService.GetProductById(1);
            ViewBag.result2 = productAttributeService.GetProductAttributeById(1);
            return View();
        }

然后运行查看效果

解析成功，展示的只是本分代码，实例代码上传到github上，喜欢的可以clone下来，自己调试调试，稍微调整下，放心用在自己的项目中，因为nop已经比较成熟了。