• 1.1 依赖
• 1.2 什么注入
• 为什么反转
• 何为容器

• 2.1 实例的注册
• 2.2 实例生命周期之单例
• 2.3 实例生命周期之Tranisent
• 2.4 实例生命周期之Scoped

• 3.1 在Startup类中初始化
• 3.2 Controller中使用
• 3.3 View中使用
• 3.4 通过HttpContext来获取

1.2 什么是注入

private ILoginService<ApplicationUser> _loginService;

public AccountController()

{

  _loginService = new EFLoginService()

}

大师说，这样不好。你不应该自己创建它，而是应该由你的调用者给你。于是你通过构造函数让外界把这两个依赖传给你。

 public

 AccountController(ILoginService<ApplicationUser> loginService)

{

  _loginService = loginService;

}

把依赖的创建丢给其它人，自己只负责使用，其它人丢给你依赖的这个过程理解为注入。

1.3 为什么要反转？

为了在业务变化的时候尽少改动代码可能造成的问题。

比如我们现在要把从EF中去验证登录改为从Redis去读，于是我们加了一个 RedisLoginService。这个时候我们只需要在原来注入的地方改一下就可以了。

 var controller = new AccountController(new EFLoginService());

controller.Login(userName, password);

// 用Redis来替换原来的EF登录

var controller = new AccountController(new RedisLoginService());


controller.Login(userName, password);

1.4 何为容器

二、.NET Core DI

2.1 实例的注册

var serviceCollection = new ServiceCollection()

  .AddTransient<ILoginService, EFLoginService>()

  .AddSingleton<ILoginService, EFLoginService>()

  .AddScoped<ILoginService, EFLoginService>();

public interface IServiceCollection : IList<ServiceDescriptor>

{

}

我们上面的AddTransient、AddSignletone和Scoped方法是IServiceCollection的扩展方法， 都是往这个List里面添加ServiceDescriptor。

private static IServiceCollection Add(

  IServiceCollection collection,

  Type serviceType,

  Type implementationType,

  ServiceLifetime lifetime)

{

  var descriptor =

  new ServiceDescriptor(serviceType, implementationType, lifetime);

  collection.Add(descriptor);

  return collection;

}

2.2 实例的生命周期之单例

public enum ServiceLifetime

{

  Singleton,

  Scoped,

  Transient

}

public interface IOperation

{

        Guid OperationId { get; }

}

public interface IOperationSingleton : IOperation { }

public interface IOperationTransient : IOperation{}

public interface IOperationScoped : IOperation{}

我们的 Operation实现很简单，可以在构造函数中传入一个Guid进行赋值，如果没有的话则自已New一个 Guid。

2.4 实例生命周期之Scoped

 var services = new ServiceCollection()

.AddScoped<IOperationScoped, Operation>()

.AddTransient<IOperationTransient, Operation>()

.AddSingleton<IOperationSingleton, Operation>();

接下来我们用ServiceProvider.CreateScope方法创建一个Scope

var provider = services.BuildServiceProvider();

using (var scope1 = provider.CreateScope())

{

    var p = scope1.ServiceProvider;
<span class="hljs-keyword">var</span> scopeobj1 = p.GetService&lt;IOperationScoped&gt;();

<span class="hljs-keyword">var</span> transient1 = p.GetService&lt;IOperationTransient&gt;();

<span class="hljs-keyword">var</span> singleton1 = p.GetService&lt;IOperationSingleton&gt;();

<span class="hljs-keyword">var</span> scopeobj2 = p.GetService&lt;IOperationScoped&gt;();

<span class="hljs-keyword">var</span> transient2 = p.GetService&lt;IOperationTransient&gt;();

<span class="hljs-keyword">var</span> singleton2 = p.GetService&lt;IOperationSingleton&gt;();

Console.WriteLine(

    $<span class="hljs-string">"scope1: { scopeobj1.OperationId },"</span> +

    $<span class="hljs-string">"transient1: {transient1.OperationId}, "</span> +

    $<span class="hljs-string">"singleton1: {singleton1.OperationId}"</span>);

Console.WriteLine($<span class="hljs-string">"scope2: { scopeobj2.OperationId }, "</span> +

    $<span class="hljs-string">"transient2: {transient2.OperationId}, "</span> +

    $<span class="hljs-string">"singleton2: {singleton2.OperationId}"</span>);

}

public void ConfigureServices(IServiceCollection services)

{

    services.AddTransient<ILoginService<ApplicationUser>,

      EFLoginService>();

    services.AddMvc();

)

ASP.NET Core的一些组件已经提供了一些实例的绑定，像AddMvc就是Mvc Middleware在 IServiceCollection上添加的扩展方法。

public static IMvcBuilder AddMvc(this IServiceCollection services)

{

    if (services == null)

    {

        throw new ArgumentNullException(nameof(services));

    }
<span class="hljs-keyword">var</span> builder = services.AddMvcCore();

builder.AddApiExplorer();

builder.AddAuthorization();

AddDefaultFrameworkParts(builder.PartManager);

...

}

3.2 Controller中使用

 private ILoginService<ApplicationUser> _loginService;

public AccountController(

  ILoginService<ApplicationUser> loginService)

{

  _loginService = loginService;

}

@using MilkStone.Services;

@model MilkStone.Models.AccountViewModel.LoginViewModel

@inject ILoginService<ApplicationUser>  loginService

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">

<head></head>

<body>

  @loginService.GetUserName()

</body>

</html>

HttpContext.RequestServices.GetService<ILoginService<ApplicationUser>>();

builder.RegisterGeneric(typeof(LoggingBehavior<,>)).As(typeof(IPipelineBehavior<,>));

builder.RegisterGeneric(typeof(ValidatorBehavior<,>)).As(typeof(IPipelineBehavior<,>));

public IServiceProvider ConfigureServices(

  IServiceCollection services){

    services.AddMvc();

    // Add other framework services
<span class="hljs-comment">// Add Autofac</span>

<span class="hljs-keyword">var</span> containerBuilder = <span class="hljs-keyword">new</span> ContainerBuilder();

containerBuilder.RegisterModule&lt;DefaultModule&gt;();

containerBuilder.Populate(services);

<span class="hljs-keyword">var</span> container = containerBuilder.Build();

<span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> AutofacServiceProvider(container);

}

4.1 有何变化