I've found that correctly implementing Dependency Injection tends to force programmers to use a variety of other programming practices that help to improve the testability, flexibility, maintainability, and scalability of code: practices like the Single Responsibility Principle, Separations of Concerns, and coding against APIs. It feels like I'm being compelled to write more modular, bite-sized classes and methods, which makes the code easier to read, because it can be taken in bite-sized chunks.

但它也倾向于创建相当大的依赖树，通过框架(特别是如果您使用约定)比手工管理要容易得多。今天我想在LINQPad中快速测试一些东西，我认为创建内核并在我的模块中加载太麻烦了，最后我手写了这个:

var merger = new SimpleWorkflowInstanceMerger(
    new BitFactoryLog(typeof(SimpleWorkflowInstanceMerger).FullName), 
    new WorkflowAnswerRowUtil(
        new WorkflowFieldAnswerEntMapper(),
        new ActivityFormFieldDisplayInfoEntMapper(),
        new FieldEntMapper()),
    new AnswerRowMergeInfoRepository());

回想起来，使用IoC框架会更快，因为模块按照约定定义了几乎所有这些东西。

Having spent some time studying the answers and comments on this question, I am convinced that the people who are opposed to using an IoC container aren't practicing true dependency injection. The examples I've seen are of practices that are commonly confused with dependency injection. Some people are complaining about difficulty "reading" the code. If done correctly, the vast majority of your code should be identical when using DI by hand as when using an IoC container. The difference should reside entirely in a few "launching points" within the application.

换句话说，如果你不喜欢IoC容器，你可能没有按照它应该做的方式来做依赖注入。

另一点:如果你在任何地方都使用反射，依赖注入真的不能手工完成。虽然我讨厌反射对代码导航造成的影响，但您必须认识到，在某些领域，它确实是无法避免的。ASP。例如，NET MVC尝试通过对每个请求的反射来实例化控制器。要手动进行依赖注入，你必须让每个控制器都成为“上下文根”，如下所示:

public class MyController : Controller
{
    private readonly ISimpleWorkflowInstanceMerger _simpleMerger;
    public MyController()
    {
        _simpleMerger = new SimpleWorkflowInstanceMerger(
            new BitFactoryLog(typeof(SimpleWorkflowInstanceMerger).FullName), 
            new WorkflowAnswerRowUtil(
                new WorkflowFieldAnswerEntMapper(),
                new ActivityFormFieldDisplayInfoEntMapper(),
                new FieldEntMapper()),
            new AnswerRowMergeInfoRepository())
    }
    ...
}

现在将其与允许DI框架为你做这件事进行比较:

public MyController : Controller
{
    private readonly ISimpleWorkflowInstanceMerger _simpleMerger;
    public MyController(ISimpleWorkflowInstanceMerger simpleMerger)
    {
        _simpleMerger = simpleMerger;
    }
    ...
}

使用DI框架，注意:

I can unit-test this class. By creating a mock ISimpleWorkflowInstanceMerger, I can test that it gets used the way I anticipate, without the need for a database connection or anything. I use far less code, and the code is much easier to read. If one of my dependency's dependency's changes, I don't have to make any changes to the controller. This is especially nice when you consider that multiple controllers are likely to use some of the same dependencies. I never explicitly reference classes from my data layer. My web application can just include a reference to the project containing the ISimpleWorkflowInstanceMerger interface. This allows me to break the application up into separate modules, and maintain a true multi-tier architecture, which in turn makes things much more flexible.

A typical web application will have quite a few controllers. All of the pain of doing DI by hand in each controller will really add up as your application grows. If you have an application with only one context root, which never tries to instantiate a service by reflection, then this isn't as big a problem. Nevertheless, any application that uses Dependency Injection will become extremely expensive to manage once it reaches a certain size, unless you use a framework of some kind to manage the dependency graph.

我支持你，瓦迪姆。IoC容器采用了一个简单、优雅且有用的概念，并使其成为您需要用200页手册学习两天的东西。

我个人很困惑，为什么IoC社区把Martin Fowler写的一篇漂亮、优雅的文章变成了一堆复杂的框架，通常只有200-300页的手册。

我尽量不去评判(哈哈!)，但我认为使用IoC容器的人(A)非常聪明，(B)对不如他们聪明的人缺乏同理心。对他们来说，每件事都很有意义，所以他们很难理解许多普通程序员会感到困惑的概念。这是知识的诅咒。理解IoC容器的人很难相信还有人不理解它。

The most valuable benefit of using an IoC container is that you can have a configuration switch in one place which lets you change between, say, test mode and production mode. For example, suppose you have two versions of your database access classes... one version which logged aggressively and did a lot of validation, which you used during development, and another version without logging or validation that was screamingly fast for production. It is nice to be able to switch between them in one place. On the other hand, this is a fairly trivial problem easily handled in a simpler way without the complexity of IoC containers.

我相信如果您使用IoC容器，您的代码将变得(坦白地说)难以阅读。为了弄清楚代码要做什么，您必须查看的地方的数量至少增加了一个。在天堂的某个地方，一位天使在呼喊。

在我看来，您已经构建了自己的IoC容器(使用Martin Fowler描述的各种模式)，并且正在询问为什么其他人的实现比您的更好。

所以，你有一堆已经工作的代码。并且想知道为什么要用其他人的实现来替换它。

考虑第三方IoC容器的优点

你可以免费修理bug 图书馆的设计可能比你的好 人们可能已经熟悉了特定的库 图书馆可能比你的快 它可能有一些您希望实现但没有时间实现的特性(您有服务定位器吗?)

Cons

你可以免费引入bug:) 图书馆的设计可能比你的还差 你必须学习一个新的API 太多你永远不会用到的功能 调试不是你写的代码通常比较困难 从以前的IoC容器迁移可能很乏味

所以，权衡利弊，做出决定吧。

As you continue to decouple your classes and invert your dependencies, the classes continue to stay small and the "dependency graph" continues to grow in size. (This isn't bad.) Using basic features of an IoC container makes wiring up all these objects trivial, but doing it manually can get very burdensome. For example, what if I want to create a new instance of "Foo" but it needs a "Bar". And a "Bar" needs an "A", "B", and "C". And each of those need 3 other things, etc etc. (yes, I can't come up with good fake names :) ).

使用IoC容器为您构建对象图可以大大降低复杂性，并将其推到一次性配置中。我只需说“给我创建一个Foo”，它就会计算出构建一个Foo需要什么。

有些人将IoC容器用于更多的基础设施，这对于高级场景来说是很好的，但在这些情况下，我同意它会使新开发人员难以阅读和调试代码。

在我看来，IoC的最大好处是能够集中配置依赖项。

如果你正在使用依赖注入，你的代码可能是这样的

public class CustomerPresenter
{
  public CustomerPresenter() : this(new CustomerView(), new CustomerService())
  {}

  public CustomerPresenter(ICustomerView view, ICustomerService service)
  {
    // init view/service fields
  }
  // readonly view/service fields
}

如果你使用静态IoC类，而不是(恕我直言)更混乱的配置文件，你可以有这样的东西:

public class CustomerPresenter
{
  public CustomerPresenter() : this(IoC.Resolve<ICustomerView>(), IoC.Resolve<ICustomerService>())
  {}

  public CustomerPresenter(ICustomerView view, ICustomerService service)
  {
    // init view/service fields
  }
  // readonly view/service fields
}

然后，你的静态IoC类看起来像这样，我在这里使用Unity。

public static IoC
{
   private static readonly IUnityContainer _container;
   static IoC()
   {
     InitializeIoC();
   }

   static void InitializeIoC()
   {
      _container = new UnityContainer();
      _container.RegisterType<ICustomerView, CustomerView>();
      _container.RegisterType<ICustomerService, CustomerService>();
      // all other RegisterTypes and RegisterInstances can go here in one file.
      // one place to change dependencies is good.
   }
}

无论何时使用“new”关键字，您都是在创建一个具体的类依赖，您的头脑中应该敲响警钟。孤立地测试这个物体变得更加困难。解决方案是对接口进行编程并注入依赖项，这样对象就可以用实现该接口的任何东西进行单元测试。模拟)。

The trouble is you have to construct objects somewhere. A Factory pattern is one way to shift the coupling out of your POXOs (Plain Old "insert your OO language here" Objects). If you and your co-workers are all writing code like this then an IoC container is the next "Incremental Improvement" you can make to your codebase. It'll shift all that nasty Factory boilerplate code out of your clean objects and business logic. They'll get it and love it. Heck, give a company talk on why you love it and get everyone enthused.

如果你的同事还没有做DI，那么我建议你先专注于DI。宣传如何编写易于测试的干净代码。干净的DI代码是比较困难的部分，一旦做到了这一点，将对象连接逻辑从Factory类转移到IoC容器应该是相对简单的。