ASP.NET Core中的依赖注入（vNext） [英] Dependency Injection in ASP.NET Core (vNext)

问题描述

目前缺少关于DI主题的文档 - 依赖注入。有人可以帮助我了解以下内容：

1. 这些注册有什么区别？

     public void ConfigureServices（IServiceCollection services）
    {
    services.AddTransient< IService，Service>（）; 
    services.AddScoped< IService，Service>（）; 
    services.AddSingleton< IService，Service>（）; 
    services.AddInstance（service）; 
   } 
     



2. 在现有解决方案中使用内置DI的优缺点是Nitject，Autofac，Structure Map）？


3. 默认依赖注入（如果有）现在有什么限制？

解决方案

对于遵循SOLID原则的任何相当大尺寸应用程序的产品开发，vNext的内置DI容器将无用，因为：

• 它不能帮助您验证配置，使得很难诊断来自常见配置错误的问题，例如俘虏依赖关系。在相当大的应用程序中，实际上很难自己发现这些错误。


• 使用拦截器或装饰器。这使得维护任何合理大小的应用程序真的很贵。


• 尽管它支持将打开的通用抽象映射到打开的通用实现，但它无法使用类型约束的泛型类型。

内置容器还有其他限制，例如只能使用单个构造函数支持类型，但这是非常合理的默认值，因为您的注射器应该只有一个构造函数。自从rc1以来，现在有了一种多功能的支持。

如果你从一个新的和简单的项目开始，我的建议是应用纯DI （这意味着手机组件没有使用容器）并通过插入您的自定义IControllerActivator 。之后，当批处理注册和装饰等功能将提高组成根目录的维护性，切换到符合您要求的已建立的DI库之一。

As currently there is lack of documentation on DI topic - Dependency Injection. Can someone help me to understand following:

1. What is the difference between these registrations?

   public void ConfigureServices(IServiceCollection services)
   {
       services.AddTransient<IService, Service>();
       services.AddScoped<IService, Service>();
       services.AddSingleton<IService, Service>();
       services.AddInstance(service);
   }
   

2. What are pros/cons of using built-in DI over existing solutions like (NInject, Autofac, Structure Map)?
3. What are current limitations of default dependency injection (if any)?

解决方案

For product development of any considerably sized application that follows the SOLID principles, vNext's built-in DI container will be useless, because:

• It doesn't help you in verifying your configuration, making it really hard to diagnose problems that come from common misconfigurations, such as Captive Dependencies. In a reasonably sized application, it's actually quite hard to spot these mistakes yourself.
• It is impossible to apply cross-cutting concerns using interceptors or decorators. This makes maintaining any reasonably sized application really expensive.
• Although it supports mapping of open generic abstractions to open generic implementations, it is unable to work with generic types with type constraints.

There are other limitations to the built-in container, such as only being able to support types with a single constructor, but this is a very reasonable default, because your injectables should only have a single constructor anyway. since rc1, there is now some kind of multi-ctor support.

If you start with a new and simple project, my advice is to apply Pure DI (which means hand-wired components without the use of a container) and resolve your types by plugging in your custom IControllerActivator. Later on, when features such as batch-registration and decoration would improve maintainability of your composition root, switch to one of the established DI libraries that fits your requirements.

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